Russia urges Iran to cooperate with IAEA on nuclear program





Russian FM tells Ahmadinejad work constructively with UNSC, open up contacts with IAEA; Iranian president launches attack on Israel at Asian security conference, says Zionism is one of history's worst ills.

 
ASTANA - Russia urged Iranian President Mahmoud Ahmadinejad on Wednesday to be "more constructive" in his cooperation with global powers on nuclear issues, Russian Foreign Minister Sergei Lavrov said.

Ahmadinejad met Russian President Dmitry Medvedev and Kazakh President Nursultan Nazarbayev after a meeting of a regional security bloc in the Kazakh capital Astana. Ahmadinejad, during his short speech at the meeting, slammed the West, the US, and Israel for causing instability and violence in the Middle East.

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Despite the Iranian president's biting speech, the Russian foreign minister said that he had encouraged Ahmadinejad to work more closely and openly with the International Atomic Energy Agency (IAEA) in their nuclear ambitions.

"We raised the question with Ahmadinejad about the necessity of more constructive cooperation with 5+1 and, more importantly, about increasing the transparency of contacts between Iran and the IAEA," Lavrov told reporters.

The 5+1 refers to the five permanent UN Security Council members and Germany.

Earlier Wednesday at the meeting, Ahmadinejad launched into a brutal attack of the West at a summit of the Shanghai Cooperation Organization on Wednesday, mentioning Zionism as one of history’s worst ills.

He said that 60 plus years of Zionism has brought only humiliation and destruction to the Palestinians and the region.

But Israel got off easy in Ahmadinejad’s tirade, viciously attacking the US and the West for a long litany that includes slavery, colonizations, the pillaging of Africa, World War I and II and numerous wars since then, dropping a nuclear bomb on defenseless civilians, and creating the atmosphere leading to 9/11 which he said was the pretext for wars in Afghanistan and Iraq which he said has cost some one million casualties.

The other leaders at the conference, including Chinese President Hu Jintao, Russian President Dmitry Medvedev, and the leaders of Kazakhstan, Kyrgyzstan, Uzbekistan,Tajikistan, India, Pakistan and Mongolia, sat impassively during his comments.

Each leader at the conference, marking the 10 years since the founding of the regional security organization that presents itself as counterbalance to NATO, spoke briefly and – with Ahmadinejad’s short exception – steered wide of the Palestinian-Israeli conflict or the current upheaval in the Middle east. The leaders also made no mention of Iran’s nuclear threat.

China, Russia, Kazakhstan, Kyrgyzstan, Uzbekistan and Tajikistan are full members of the organization, which promotes economic, military and security cooperation. Iran, Pakistan, India, and Mongolia enjoy observer status.

Because of UN sanctions against it, Iran is presently barred from joining as a full member. 
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Former USFK Commander Talks About Nuke Threat on Korean Peninsula

The Asan Plenum nuclear conference is currently underway in Seoul which is a gathering of leading think tanks to discuss pressing challenges related to nuclear weapons and power.

And among the 250 participants of leading nuclear experts around the world was the former commander of the US Forces Korea, Burwell Bell, who shared his assessment of the current security situation on the Korean peninsula.

And our Kim Nari, who talked with Mr. Bell joined us in the studio.
Welcome Nari.

[Interview : ] Thank you.
The three-day Asan Plenum forum under the topic 'Our Nuclear Future' began on Monday and is currently underway in Seoul.
I was at the forum on the opening day and was able to meet up with the former commander of US Forces Korea, Burwell Bell, who is visiting Seoul as a panelist for the forum.
He shared his opinions and assessment of the current security situation here including his belief that North Korea will continue its provocative acts.
Mr. Bell also said China is holding the key for achieving peace and stability on the Korean peninsula and that only strong retaliation by South Korean and American forces can stop future North Korean attacks.
Let's take a look.

Retired US Army General Burwell Bell said China is the missing ingredient for maintaining peace on the Korean peninsula.


[Interview : US Army Gen. Burwell Bell
Former USFK commander] "The missing ingredient is China. China is missing. They are in favor of the status quo, this makes the region very volatile, great risk. And they would prefer status quo other than North Korea that is moving towards reconciliation with the South."

General Bell, who is in Seoul attending the Asan Plenum nuclear forum as a panelist said that in order for the six-party nuclear talks to succeed all the member nations, excluding North Korea, should share the common goal.


[Interview : US Army Gen. Burwell Bell
Former USFK commander] "Only when all five of the other parties have similar interest in the denuclearization of North Korea, will we be able to effectively approach the North. That leadership should come from China. And to this date, they have chosen not to behave in a way that will make a positive difference on the Korean peninsula. "

He also said he wouldn't be surprised to see further provocative acts by the North in the near future.


[Interview : US Army Gen. Burwell Bell
Former USFK commander] "They will continue to conduct provocations as far as they can, as long as they can, in hopes of achieving their aims."

And he explained that the poor economic situation the reclusive country currently faces is the main drive of the North's continuous strikes.


[Interview : US Army Gen. Burwell Bell
Former USFK commander] "The potential of military provocations in hopes of bringing South Korea, the United States and Japan and others to the diplomatic table to gain economic concession remains very serious issue, and would not surprised for me to see something along those lines in not too distant future.

Then how could we deal with the situation[Interview : US Army Gen. Burwell Bell
Former USFK commander] "Now the question is not will North Korea conduct another provocation because it inevitably will but how will the Republic of Korea and their best ally the United States respond militarily."

Bell, who served for two years as US Forces Korea commander before retiring in 2008, says strong retaliation is the answer.


[Interview : US Army Gen. Burwell Bell
Former USFK commander] "A strong retaliatory strike. I hope that the next time when North Korea strikes the South, that South Korea with the United States supporting them, should respond and retaliate for the previous strikes that have happened, recently the Cheonan and the island."

And he said there is no doubt that the combined forces of South Korea and the United States can defeat the North.


[Interview : US Army Gen. Burwell Bell
Former USFK commander] "Between ground forces and American naval and air forces partnered with Korean air and naval forces, this is a overwhelming force. The question is, can that formation stop a North Korean attack, punish the North Koreans, and set the conditions as appropriate for offensive operation. The answer is, you bet it can."


I am sure based on his experience as the commander of US Forces here that he is well aware of the current security situation on the peninsula, but it is certainly not comforting to hear that we can expect another attack by North Korea in the near future.

[Reporter : ] Right.
I don't want to say we are 'immune' to North Korea's possible threats as we have been exposed to this volatile situation for over six decades, but unfortunately it is true that we are living in an environment threatened by North Korea at any time.
But as Mr. Bell said it is not the time to think about whether the North will strike again, and if it does, when it might happen but rather, how can we stop this ongoing volatile situation from expanding.
And as you heard he recommends that strong retaliation is the only way.

Switching to the Asan Plenum tell us more about this conference.

[Reporter : ] Well, this year's Asan Plenum nuclear forum focuses on five major themes: nonproliferation, disarmament, peaceful use, nuclear security, and deterrence.
And with Seoul set to host the second Nuclear Security Summit next year, the recent nuclear crisis in Japan, as well as North Korea's pursuit of nuclear weapons the conference will play an important role in setting the global agenda on nuclear issues.

Thank you Nari for that report.

[Reporter : ] My pleasure.

JUN 15, 2011
 
Reporter : narikim@arirang.co.kr

'More pain, more gain' policy needed to break NK stalemate: expert

'More pain, more gain' policy needed to break NK stalemate: expert

Bruce Klingner, a senior fellow at the Heritage Foundation
By Kim Young-jin

The United States should pursue more aggressively its two-track policy toward Pyongyang of sanctions and diplomacy to break the stalemate over its nuclear program and decrease “a very high risk” of further provocations, an expert said Wednesday.

“The two-track policy is a good one, but it has been weakly implemented,” Bruce Klingner, a senior fellow at the U.S.-based Heritage Foundation, said on the sidelines of a nuclear forum in Seoul. “But more needs to be done on both tracks. We need more pain and more gain.”

His remarks came amid a deepening stalemate over the North Korean nuclear program after the North threw cold water on efforts to revive multilateral negotiations by vowing never to deal with the Lee Myung-bak administration.

He said the Obama government should start by fixing loopholes in U.N. Security Council resolutions so the North feels the full brunt of the sanctions, especially over its suspected proliferation activities.

Klinger added that the United States should also target the countries the North is proliferating to, as the resolutions on Pyongyang apply to all member nations.

“So far the U.S. and the U.N. have been reluctant to target non-NK targets. Clearly Iran, Burma and Syria, their entities there should be targeted and it’s extremely likely that Chinese companies and banks are involved,” he said.

On May 26, a North Korean freighter suspected of containing illicit weapons and apparently en route to Myanmar was intercepted by a U.S. destroyer in waters off China. Access to the ship was denied, but it turned around and headed back to the North.

But Washington must also make clearer to Pyongyang, the benefits of changing its behavior, Klingner said.

“We need to present them a menu of benefits,” he said, listing humanitarian aid, economic development assistance, removal of sanctions and a gradual improvement of diplomatic relations among the incentives. The message could be delivered by Stephen Bosworth, Washington’s special envoy on North Korea.

The stalemate has raised concerns that Pyongyang could launch fresh attacks following two deadly ones last year.

The former CIA deputy division chief warned that Washington and Seoul’s growing skepticism over the ability to solve the nuclear issue diplomatically could cause the North to launch bolder provocations, saying there was even a “very high risk” of such an act within South Korea.

“This could be a terrorist attack or a demonstration that they were able to target a nuclear reactor here, leaving behind an indication that a North Korean commando team had been there,” he said.

Among other actions could be the instigation of skirmishes in the West Sea or a land clash along the heavily-fortified Demilitarized Zone that straddles Korea, he said. It could also test-fire a ballistic missile as far as 4,000 miles or conduct a uranium-based nuclear test, both of which would undoubtedly set off major alarms internationally.

Washington and Seoul must maintain a third track of maintaining sufficient defenses against multifaceted threats from the North, including missile defense and non-proliferation efforts, he said.

Many analysts believe that despite the North’s repeated statements that it wishes to return to the denuclearization forum, it is intent on keeping its program given the resources it has put into it.

“Under the current paradigm, the North is unlikely to decide to give up its nuclear weapons. We have to change their cost-benefit analysis so it sees it’s more in its interest to give them up. But the ball is in its court.”

He said Pyongyang could allow IAEA inspectors back into its main Yongbyon nuclear plant and resume previously agreed-upon “tangible first steps” to cool tensions and get dialogue back on track.

“Then Washington would be more likely to resume food aid and come back to talks and suggest that Seoul resume contacts as well,” he said.
yjk@koreatimes.co.kr

Russia tells Iran to improve nuclear behaviour


Russian President Dmitry Medvedev (right) on Wednesday urged Iranian counterpart Mahmoud Ahmadinejad (left) to take a more constructive approach in the standoff with world powers over Teheran's nuclear drive.


ASTANA - RUSSIAN President Dmitry Medvedev on Wednesday urged Iranian counterpart Mahmoud Ahmadinejad to take a more constructive approach in the standoff with world powers over Teheran's nuclear drive.
Mr Medvedev requested a meeting with Mr Ahmadinejad on the sidelines of a regional summit in the Kazakh capital to refocus global attention on the Iranian nuclear problem, Russian Foreign Minister Sergei Lavrov told reporters.
'This problem seems to have moved to the back burner while other members of the negotiating process remain busy with the Middle East and North Africa,' Interfax quoted Mr Lavrov as saying.
'Although we are also very concerned about what is happening in this region, we feel it is wrong to forget about the deadlock that remains around the Iranian nuclear programme,' Russia's top diplomat said.
'At the meeting, the Iranian president was told of the need for more constructive cooperation with the 'six' - and, most importantly, of improving transparency his contacts with the IAEA.'
Mr Lavrov was referring to the UN nuclear watchdog and the stalled six-party negotiations, which also include Germany and the five permanent UN Security Council members. -- AFP

Japan Proposes Tepco Aid Package, With Fight Likely

TOKYO—The Japanese government proposed creating a financial safety net for beleaguered Tokyo Electric Power Co. to help it pay claims that could total more than $100 billion stemming from its damaged nuclear power plant—a proposal that drew support from investors but could face tough odds in Japan's deadlocked parliament.
Reuters
Japan's Prime Minister Naoto Kan used a fan while attending a legislative committee on Japan's reconstruction efforts Tuesday.
If it passes, the plan could keep the company—known as Tepco—from insolvency while sparing its lenders a painful restructuring. But in a shift, it also opens the door for higher electricity bills for consumers and businesses, in addition to contributions from the Japanese power and nuclear industries and backing from the Japanese government. Previously, government officials had appeared to rule out any rate increases to finance the rescue.
The government's plan didn't offer details on how much each would bear, suggesting fights over the final structure lie ahead. "The government will make sure that any costs passed on to consumers will be kept to a minimum," Minister of Economy, Trade and Industry Banri Kaieda said at a briefing.
Tepco shares soared on the news, climbing the 25% limit allowed for a single day, to close at ¥249 (about $3.11) in a strong rebound from a recent descent to an all-time low of ¥148 hit Friday. Tepco bonds, which have seen little trading due to their uncertain future, also rose strongly.
But the chairman of the Federation of Electric Power Companies of Japan gave a more guarded reaction, saying the utility lobby wants to see stronger justification for payments by other utilities to help finance the compensation payments. He said the group hopes its demands will be better reflected in parliamentary deliberations.
The main opposition party, the Liberal Democrats, also said it isn't necessarily in favor. Support from the opposition would be needed to ensure passage of the bill, but other legislation—including bills to help fund rebuilding after the devastating earthquake and tsunami that struck Japan on March 11 —has stalled as opposition lawmakers press for the ouster of unpopular Prime Minister Naoto Kan.
"It's a problematic scheme that demands payments from other power companies that aren't at fault, and holds [Tepco] accountable for limitless compensation," said Nobuteru Ishihara, LDP secretary general.
Under the plan, the government will create a special body to handle the claims, which estimated have put at up to ¥10 trillion, or $124 billion. It will have the authority to issue government-backed bonds and will repay the funds using future profits from Tepco, contributions from industry and potentially higher power bills. The government also said that it will stand behind the company if necessary and that it isn't considering bankruptcy.
The government said in a statement that it "has asked Tepco to seek cooperation from all stakeholders," which it said included shareholders, bondholders and lending banks. But it added that a decision on what constituted "cooperation" would be left to the new government body.
"It is not for the government to decide specific forms of cooperation between Tepco and the stakeholders," Shinsuke Kitagawa, head of a task force on nuclear damages compensation, said at a briefing.
Investors were reassured that the government's plan wouldn't mandate a wholesale restructuring of Tepco's loans or bonds. "We view this establishment of the framework as major progress. The scheme will allow Tepco to fulfill its responsibility to pay compensation costs without going bankrupt, which implies that bonds will avert a default," said Toshiyasu Ohashi, chief credit analyst at Daiwa Securities Capital Markets Co.
Analysts said that restrictions imposed Tuesday on the short-selling of Tepco shares also played a role in the sharp share price rise.
Tepco has already warned that it faces a dire financial future as it tries to cope with the cleanup from the disaster at the Fukushima Daiichi plant, which was heavily damaged by the March 11 earthquake and tsunami. It is also struggling to fill in large gaps in its generating capacity. Even after it brought on mothballed facilities, Tepco is expecting a shortfall of 10% over usual summer demand.
Tepco President Masataka Shimizu said that the utility is preparing for making compensation as quickly as possible, slightly more than three months after the quake and tsunami. "We hope the bill will be enacted as soon as possible," he said.
The legislation is based on a framework initially announced on May 13 as the government grappled with how to meet the multiple interests of those hit by the accident, the utilities customers, and the company's shareholders, bondholders and lenders.
An independent panel of outside experts that is scrutinizing Tepco's finances will meanwhile hold its first meeting Thursday. Mr. Kaieda said the panel will ensure Tepco sells assets and implement tough cost-cutting before seeking any public support.
—Judy Lam and Kana Inagaki contributed to this article.

Japan cabinet approves Fukushima nuclear compensation

Cabinet agrees estimated $100bn-plus payout package after reactor meltdown but political manoeuvring could delay payments
  • guardian.co.uk,
  • Article history
  • Fukushima nuclear disaster
    Fukushima nuclear disaster: Trucks drive past piles of rubble collected after the tsunami and nuclear disaster. Photograph: Kiyoshi Ota/Getty Images
    Japan's government has approved a plan to help the owners of the stricken Fukushima Daiichi nuclear plant provide trillions of yen in compensation, but political manoeuvring could delay payments to tens of thousands of victims of the country's nuclear crisis. The cabinet's approval of the scheme on Tuesday came after the plant's operator, Tokyo Electric Power [Tepco], said a further six workers had exceeded the annual legal dose of radiation, underlining the risks they face as they struggle to stabilise overheating nuclear reactors by early next year. Shares in Tepco rose dramatically after the compensation scheme was approved, but anger is mounting at the slow progress made in paying families and businesses more than three months after the worst nuclear accident since Chernobyl. Under the bill, the government would set up a fund and issue special bonds to enable Tepco to pay compensation that the Mainichi newspaper said could reach US$124bn (£75bn). Other power utilities would be asked to contribute to the fund, and Tepco is expected to repay the full sum over an, as yet, unspecified number of years. In return for state help, Tepco will have to cut costs and turn its management over to the government "for a certain period of time". Tepco, whose share price has fallen 90% since the 11 March tsunami crippled the Fukushima Daiichi plant, promised to make repayments as quickly as possible. "We hope that the proposed bill will be enacted in parliament as soon as possible," it said in a statement. The measure's fate is far from certain, however. Some government and opposition MPs oppose the use of public funds to help Tepco, and the prime minister, Naoto Kan, is still under pressure to resign immediately despite surviving a recent no-confidence motion by promising to step down once the crisis is under control. The current parliamentary session is due to end on 22 June, but the Kan administration is pushing to extend it in the hope of passing the compensation package, as well as an emergency budget to fund post-tsunami reconstruction. News that the bill had gained cabinet approval lifted investor confidence in Tepco, but concern persists that the company will look to consumers to help fund damages claims in the form of higher electricity bills. The trade and industry minister, Banri Kaieda, denied media reports that the government had already approved a 16% increase in electricity charges from next April. "The government will make sure that any costs passed on to consumers will be kept to a minimum," he said. Tepco and two other power utilities are coming under pressure to end their involvement in nuclear power, with groups of investors expected to raise the issue at shareholders meetings at the end of the month. The risks facing the thousands of workers who have taken part in the operation to stabilise Fukushima Daiichi were underlined when Tepco said six more were feared to have exceeded the legal limit of 250 millisieverts [mSv] a year, bringing the total to eight. The limit was raised from 100mSv a year early in the crisis to allow workers to spend more time at the plant, where nuclear fuel in three reactors suffered meltdowns. In the worst cases, two control room workers were exposed to well over twice the legal limit, Tepco said, as it released preliminary results of radiation tests on almost 2,400 workers who were based at the plant in March, when radiation levels were at their highest. The health ministry also said on Monday that at least 90 others have exceeded the original limit of 100mSv, including several who are nearing the 250mSv level. Experts believe that exposure to more than 250mSv increases the chances of a person developing cancer in their lifetime by 1%. Hidehiko Nishiyama, a spokesman for Japan's nuclear and safety agency, described the findings as "extremely regrettable". Tepco said none of those affected have showed signs of ill health, but added that they would need long-term monitoring.

Italy referendums deal blow to Berlusconi

Australian Broadcasting Corporation
Broadcast: 14/06/2011
Reporter: Emma Alberici
Italians have turned their backs to president Silvio Berlusconi by voting against government plans at three referendums.

Transcript

ALI MOORE, PRESENTER: Results in the Italian referendums held over the weekend have struck a blow to Silvio Berlusconi's government.

Voters have overwhelmingly decided against nuclear energy, they don't want to privatise the country's water utilities and they also made it clear that government ministers should not be immune from prosecution.

Europe correspondent, Emma Alberici.

EMMA ALBERICI, REPORTER: Those who turned up to celebrate on the streets of Rome cheered as much for their success at the polls as they did for their chance to send a message to their prime minister.

JAMES WALSTON, AMERICAN UNIVERSITY OF ROME: Berlusconi is clearly out of favour with the majority of Italians, for one reason or another. He has tried so far to deal with his lack of support in the local elections, and now in the referendums, by ignoring the signs. He pretends that everything is alright.

EMMA ALBERICI: These were not compulsory elections and the Italian government spent $400 million trying to convince voters to stay away from the ballot box. Without a 50 per cent turnout, the referendum would not have been valid.

But not only did an overwhelming majority of Italians show up, 94 per cent of them voted yes to scrap Mr Berlusconi's plan to reintroduce nuclear power, which was abandoned in 1987 after the Chernobyl disaster.

In a country that's prone to earthquakes, Fukushima looms large.

SALVATORE BARBERA, GREENPEACE ITALY: 22 million and a half Italian people said 'Si'. Si means 'I don't want nuclear in this country' and this means that the only possibility is to go to renewable. Germany, Japan, Switzerland, now Italy.

EMMA ALBERICI: The prime minister had hoped that Italy would meet 25 per cent of its electricity needs with nuclear energy by 2030. Now it will need to rely more heavily on the renewable sector which already makes up 22 per cent of the country's power supplies.

SILVIO BERLUSCONI, ITALIAN PRIME MINISTER (TRANSLATION): Due to the decision that the Italian people are taking right now with the referendum, we will have to say goodbye to nuclear power plants. So now we will have to commit to the renewable sector.

EMMA ALBERICI: As counting ends in the three referenda it's clear the voters also said no to placing their prime minister and his cabinet above the law by allowing them to avoid court cases against them by claiming to be too busy to attend proceedings.

Italians rejected, too, Mr Berlusconi's proposal to privatise the state's water assets.

JAMES WALSTON: He's been the centre of Italian politics for 17 years, any vote that the Italians have taken over the last 17 years has in some way been a vote on Berlusconi and this one is no exception.

EMMA ALBERICI: The setback for the government comes just weeks after defeat for the ruling party in local elections. Mr Berlusconi's party lost control in important cities like Milan and Naples, but this time his coalition partner, the far right Northern League, also suffered heavy losses.

A general election isn't due to be held in Italy until 2013.

Emma Alberici, Lateline.

Italians Vote to Abandon Nuclear Energy

Zuma Press
Silvio Berlusconi in Rome on Monday.
ROME—Italians voted to abandon nuclear power for the foreseeable future, turning out in droves to cast ballots in a packet of referenda whose outcome is a sign of growing popular discontent toward Prime Minister Silvio Berlusconi's conservative government.
Mr. Berlusconi's administration had in past weeks urged people not to vote in the four referenda, which were organized by center-left opposition parties and which asked voters whether they wanted to overturn government laws on reviving nuclear energy, privatizing Italy's water supply and giving top government officials partial immunity from prosecution.
Instead, 57% of Italians went to the polls—a number well above the 50% of the voting population needed to make a referendum valid, a threshold last reached in 1995. More than 95% of those who cast their ballots voted "yes" in each referendum, overturning the four laws in question.
"This was a vote against nuclear energy. But by urging people not to go to the polls, Berlusconi turned this into a vote against himself," said Giovanni Sartori, professor emeritus of political science at the University of Florence.
Mr. Berlusconi had made restarting nuclear energy in Italy one of his government's priorities. The immunity law also had been one of the government's key planks. The law allows the prime minister and other top officials not to show up in court for criminal trials, if busy governing schedules are cited. Critics, however, have long characterized the law as a tailor-made measure aimed at shielding Mr. Berlusconi from the four criminal trials he is currently facing.
On Monday, the prime minister acknowledged the defeat.
"On each theme, Italians have made their position clear. The government and Parliament will now have to take into account this result," Mr. Berlusconi's office said in a statement.
Monday's outcome is notable not just for the lopsided vote but also because it comes just weeks after Mr. Berlusconi's conservative coalition was badly defeated in local elections. Though the premier still has the majority in Parliament he needs to govern, his popularity has been falling in recent months.
Italy's center-left opposition parties, which had widely campaigned for people to vote, were jubilant. Opposition leader Pierluigi Bersani hailed the result as a crucial sign of the need for political change and called for Mr. Berlusconi's government to resign.
"This referendum marks a divorce between the Italians and the government. At this point, the government has to leave and lead to new elections," Mr. Bersani told a news conference.
Conservative government officials tried to play down the political meaning of the vote. "The fact that the referenda reached the quorum doesn't change anything for the government," said Ignazio La Russa, Italy's Defense Minister and a strong Berlusconi supporter.
Italy's chronically feeble economy, however, is weighing heavily on young people in particular, and many here are fed up with the premier's legal woes, including most recently his trial on charges of paying for sex with an underage woman and abusing his power to cover it up—charges the premier denies.
The Northern League, Mr. Berlusconi's party's most important ally in Parliament, also is getting fed up. "Two weeks ago, we got a first slap in the face in local elections. Now the referendum has dealt us a second slap in the face," said Roberto Calderoli, Italy's minister for legislative simplification and a key Northern League official.
Italy abandoned nuclear energy in 1987—shortly after the Chernobyl nuclear accident—by voting against it in a referendum similar to Monday's. In the current vote, the Fukushima Daiichi nuclear crisis in Japan drew people to the polls. As in other European countries, Italy earlier this year imposed a moratorium on its nuclear plans, but Mr. Berlusconi's government was hoping to resurrect them longer term by building several plants across the country. Early on Monday, as the results were coming in, Mr. Berlusconi said that without the possibility of nuclear plants, Italy would have to "strongly commit" to renewable energy.
Many others pushed for a nuclear revival in the country. "Italy will spend a lot of money for energy needs" without nuclear energy, said Chicco Testa, head of Italy's Nuclear Forum and former chairman of Italian utility Enel SpA. Mr. Testa was one of the main backers of the 1987 referendum against nuclear power, but has since changed his stance: "There is plenty of gas out there and coal, but I don't know what the prices will be in 10 years' time as they are tied to oil. Based on past experience, I see higher oil prices."
The two water-related referenda asked Italians to vote on whether to overturn the government's plans to privatize water utilities. The government has argued that handing over water management to private entities would make it more efficient. Critics argued successfully that it would lead to higher prices.
Write to Giada Zampano at giada.zampano@dowjones.com

No to nuclear and no to Berlusconi


A giant mock nuclear waste barrel built by anti-nuclear protesters stands in central Rome, 7 June Anti-nuclear protesters erected this giant mock nuclear waste barrel in Rome
In the past two days the people of Italy have been given their say.
They have convincingly rejected nuclear power and they have delivered another humiliating defeat to Italian Prime Minister Silvio Berlusconi.
The disaster at the Fukushima nuclear power plant in Japan is changing Europe's energy future. Increasingly it looks as if it may become a continent without nuclear power.
The French have bet heavily on the nuclear industry providing clean energy. Given the chance, Europe's citizens are saying "no way".
Eyes on France On 30 May, Germany, Europe's economic powerhouse, decided to phase out atomic power between 2015 and 2022. Switzerland looks set to follow. It is examining a proposal to phase out the country's nuclear plants by 2034.

Start Quote

[The Italian vote] could open a serious phase of reflection in other [EU] member states”
Daniel Cohn-Bendit Green leader, European Parliament
Now Italy will not revive its nuclear industry. The people have spoken and spoken convincingly.
Silvio Berlusconi had urged his supporters to boycott the polls, hoping that the turnout would not reach the necessary threshold of 50%.
In the end, 56% of voters took part and afterwards the prime minister conceded: "We will have to commit strongly to the renewable energy sector."
The leader of the Greens in the European Parliament, Daniel Cohn-Bendit, said this vote "could open a serious phase of reflection in other member states".
If Europe moves away from nuclear power, a question arises as to whether it can fill the gap with renewable energy. Will the mood in France change and will they, too, get a chance to vote?
Evaporating magic
Italian Prime Minister Silvio Berlusconi attends a television programme in Rome, 25 May Silvio Berlusconi looks more and more isolated
There was a second plot to the vote in Italy: Silvio Berlusconi himself. Last month, in elections he made about himself and his authority, his candidates were badly beaten. Now he has suffered a serious defeat on a number of referendum questions.
The public rejected plans to privatise the water system. Even the Vatican got involved, declaring that water was a human right and should not be subject to market forces.
Most significantly, the people rejected a change in the law that would have enabled the Italian leader and other high officials to avoid prosecution.
Berlusconi's appeal to the Italian electorate, which has long survived gaffes and scandals, is now ebbing away.
The magic has gone. That bond between Berlusconi and ordinary Italians seems to have snapped. Perhaps voters have become weary of a leader where so much of public debate is about his personal life and his political survival?
Pierluigi Bersani, leader of the main opposition Democratic Party, was calling on Mr Berlusconi to resign. "This referendum," he said, " was about the divorce between the government and the country."
Berlusconi still has a majority in parliament but it is dependent on the Northern League. They are now questioning whether their alliance with Berlusconi's party is damaging them. Some may decide it is time to break away.
Next week there were be a vote on confidence in the Italian parliament. It is not in Mr Berlusconi's character to step down but he is increasingly an isolated figure. He has a fragile majority in parliament but almost certainly not in the country.

Cabinet OKs Tepco redress bill

Other utilities must ante up to back huge outlays

Kyodo
The Cabinet approved a bill Tuesday to help Tokyo Electric Power Co. meet its massive compensation payments through the creation of an entity that would provide financial assistance to the utility strugging with the crisis at the Fukushima No. 1 nuclear plant.
Now that it has the administration's endorsement, the bill is expected to be submitted to the current Diet session. The administration is hoping to ensure swift payment of compensation that may total trillions of yen while maintaining a stable supply of electricity.
But the bill's fate is uncertain amid the political tug of war that pressured Prime Minister Naoto Kan into announcing he will resign in the near future. Some, including lawmakers of the Democratic Party of Japan, are also concerned that the compensation scheme may lead to a rise in electricity fees.
Under the bill, the new institution would be allocated a type of bond from the government that can be cashed when necessary and could receive loans from financial institutions so it can provide financial assistance to Tepco.
Based on the idea of mutual help, electricity firms that own nuclear plants would contribute to the entity.
Although the bill is intended to prepare for possible future nuclear accidents, its main purpose for now would be to help Tepco meet compensation demands and prevent the utility from being crushed by debt.
The nuclear emergency, triggered by the quake-tsunami disaster on March 11, has forced many residents around the plant in Fukushima Prefecture to evacuate their homes and has devastated the region's agriculture, livestock and fishing industries.
The DPJ-led administration at one point planned to delay submission of the bill to a later Diet session but has decided to present it during this session so victims can benefit more quickly.
It is also seeking early passage of the bill in the hope of allaying concerns among market players about Tepco's outlook, which have sent its shares tumbling on stock markets.
The DPJ is hoping to extend the current session beyond the scheduled end of June 22.

Disaster prep rethink

The government sees the need to rethink how it views the threat of future major earthquakes and their potential damage as well as measures local governments and people in harm's way may need to take, according to a report released Tuesday.
In the 2011 white paper for disaster prevention approved by the Cabinet, the government describes the March 11 quake and tsunami as a "disaster that exceeded the envisioned scenarios in disaster prevention measures taken thus far."
Summarizing the extent of damage and the central government's response to it, the annual report notes, "Improving the lives of victims, who are hanging tough under great stress, is the priority issue."
More than 15,000 people were killed and about 8,000 others remain missing in the quake and tsunami that devastated the northeast.
On future steps, the paper emphasizes the importance of coming up with broad-based measures to tackle the possible situation of three major earthquakes occurring simultaneously in regions ranging from eastern to southwestern Japan.
It says that tsunami observation systems should be reinforced while also taking into consideration unexpectedly vast damage they might cause, adding that evacuation drills should be held to prepare for tsunami and disaster facilities should be upgraded.
The document includes an outline of the nuclear crisis at the Fukushima No. 1 power plant but doesn't mention that three reactors suffered core meltdowns.

Nuclear weapons delivery

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Nuclear weapons
Fat man.jpg
History
Warfare
Arms race
Design
Testing
Effects
Delivery
Espionage
Proliferation
Arsenals
Terrorism
Anti-nuclear opposition
Nuclear-armed states
United States · Russia
United Kingdom · France
China · India · Israel
Pakistan · North Korea
South Africa (former)
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Nuclear weapons delivery is the technology and systems used to place a nuclear weapon at the position of detonation, on or near its target. Several methods have been developed to carry out this task.
Strategic nuclear weapons are used primarily as part of a doctrine of deterrence by threatening large targets, such as cities. Weapons meant for use in limited military maneuvers, such as destroying specific military, communications, or infrastructure targets, are known as tactical nuclear weapons. In terms of explosive yields, nowadays the former have much larger yield than the latter, although it is not a rule. The bombs that destroyed Hiroshima and Nagasaki in 1945 (with TNT equivalents between 15 and 22 kilotons) were weaker than many today's tactical weapons, yet they achieved the desired effect when used strategically.

[edit] Main delivery mechanisms

[edit] Gravity bomb

The first nuclear weapons, such as the "Little Boy" and the "Fat Man" devices, were large and cumbersome gravity bombs.
Historically the first method of delivery, and the method used in the two nuclear weapons actually used in warfare, was in a gravity bomb dropped by a bomber. In the years leading up to the development and deployment of nuclear-armed missiles, nuclear bombs represented the most practical means of nuclear weapons delivery; even today, and especially with the decommissioning of nuclear missiles, aerial bombing remains the primary means of offensive nuclear weapons delivery, and the majority of U.S. nuclear warheads are represented in bombs.
No nuclear weapon qualifies as a "wooden bomb"—US military slang for a bomb that is trouble-free, maintenance-free, and danger-free under all conditions. Gravity bombs are designed to be dropped from planes, which requires that the weapon can withstand vibrations and changes in air temperature and pressure during the course of a flight. Early weapons often had a removable core for safety, installed by the air crew during flight. They had to meet safety conditions, to prevent accidental detonation or dropping. A variety of types also had to have a fuse to initiate detonation. US nuclear weapons that met these criteria are designated by the letter "B" followed, without a hyphen, by the sequential number of the "physics package" it contains. The "B61", for example, was the primary bomb in the US arsenal for decades.
Various air-dropping techniques exist, including toss bombing, parachute-retarded delivery, and laydown modes, intended to give the dropping aircraft time to escape the ensuing blast.
The early gravity nuclear bombs could only be carried by the B-29 Superfortress. The next generation of weapons were still so big and heavy that they could only be carried by bombers such as the B-52 Stratofortress and V bombers, but by the mid-1950s smaller weapons had been developed that could be carried and deployed by fighter-bombers.

[edit] Ballistic missile

Missiles using a ballistic trajectory usually deliver a warhead over the horizon, at distances of hundreds up to thousands of kilometers, as in the case of intercontinental ballistic missiles (ICBMs) and submarine-launched ballistic missiles (SLBMs). Most ballistic missiles exit the Earth's atmosphere and re-enter it in their sub-orbital spaceflight.
Placement of nuclear missiles on the low Earth orbit, a truly fearsome option, has been banned by Outer Space Treaty as early as 1967. Also, the eventual Soviet Fractional Orbital Bombardment System (FOBS) that served a similar purpose—it was just deliberately designed to deorbit before completing a full circle—was phased out in January 1983 in compliance with the SALT II treaty.
An ICBM is more than 20 times as fast as a bomber and more than 10 times as fast as a fighter plane, and also flying at a much higher altitude, and therefore more difficult to defend against. ICBMs can also be fired quickly in the event of a surprise attack.
Early ballistic missiles carried a single warhead, often of megaton-range yield. Because of the limited accuracy of the missiles, this kind of high yield was considered necessary in order to ensure a particular target's destruction. Since the 1970s modern ballistic weapons have seen the development of far more accurate targeting technologies, particularly due to improvements in inertial guidance systems. This set the stage for smaller warheads in the hundreds-of-kilotons-range yield, and consequently for ICBMs having multiple independently targetable reentry vehicles (MIRV). A single missile would now be used to launch an entire "bus", releasing up to a dozen independent warheads into a dozen different ballistic trajectories. MIRV has a number of advantages over a missile with a single warhead. With small additional costs, it allows a single missile to strike multiple targets, or to inflict maximum damage on a single target by attacking it with multiple warheads. It makes anti-ballistic missile defense even more difficult, and even less economically viable, than before.
Missile warheads in the American arsenal are indicated by the letter "W"; for example, the W61 missile warhead would have the same physics package as the B61 gravity bomb described above, but it would have different environmental requirements, and different safety requirements since it would not be crew-tended after launch and remain atop a missile for a great length of time.

[edit] Cruise missile

Cruise missiles have a shorter range than ICBMs. BGM-109 Tomahawk pictured.
A cruise missile is a jet engine or rocket-propelled missile that flies at low altitude using an automated guidance system (usually inertial navigation, sometimes supplemented by either GPS or mid-course updates from friendly forces) to make them harder to detect or intercept. Cruise missiles can carry a nuclear warhead. They have a shorter range and smaller payloads than ballistic missiles, so their warheads are smaller and less powerful.
Unlike conventional cruise missiles, which sometimes use cluster munition payloads, and unlike bombers, nuclear armed cruise missiles have a single warhead.
The AGM-129 ACM (Advanced Cruise Missile) is the US Air Force's current nuclear-armed air-launched cruise missile. The START II treaty forbids the USA from using stealth weapons on stealth aircraft, therefore the ACM is only carried on the B-52 Stratofortress. This plane can carry 20 missiles. Thus the cruise missiles themselves can be compared with MIRV warheads. The BGM/UGM-109 Tomahawk sea-launched cruise missile is capable of carrying nuclear warheads, but does not in present configurations.
Cruise missiles may also be launched from mobile launchers on the ground, and from naval ships.
There is no letter change in the US arsenal to distinguish the warheads of cruise missiles from those for ballistic missiles.
Cruise missiles, even with their lower payload, have a number of advantages over ballistic missiles for the purposes of delivering nuclear strikes:
  • Launch of a cruise missile is difficult to detect early from satellites and other long-range means, contributing to a surprise factor of attack.
  • That, coupled with the ability to actively maneuver in flight, allows for penetration of strategical anti-missile systems aimed at intercepting ballistic missiles on calculated trajectory of flight.
Partially for those reasons, nuclear-armed cruise missiles are amongst the least deployed of all nuclear weapons, as their deployment is restricted by treaties such as SALT II.

[edit] Other delivery systems

The Davy Crockett artillery shell is the smallest known nuclear weapon developed by the USA.
The Mk-17 was an early U.S. thermonuclear weapon and weighed around 21 short tons (19,000 kg).
Other potential delivery methods include artillery shells, mines such as the Medium Atomic Demolition Munition and the (very odd) Blue Peacock, and nuclear depth charges, and nuclear torpedoes. An atomic mortar was also tested. Even an 'Atomic Bazooka' was designed to be used against large formations of tanks.
In the 1950s the U.S. developed small nuclear warheads for air defense use, such as the Nike Hercules. From the 1950s to the 1980s, the United States and Canada fielded a low-yield nuclear-tipped air-to-air rocket, the AIR-2 Genie. Further developments of this concept, some with much larger warheads, led to the early anti-ballistic missiles. United States' have taken nuclear air-defense weapons out of service. Russia continues to maintain the Soviet anti-ballistic missiles with nuclear warheads.[citation needed]
Small, two-man portable tactical weapons (erroneously referred to as suitcase bombs), such as the Special Atomic Demolition Munition, have been developed, although the difficulty to combine sufficient yield with portability limits their military utility.

[edit] See also

Nuclear weapon design


The first nuclear weapons, though large, cumbersome and inefficient, provided the basic design building blocks of all future weapons. Here the Gadget device is prepared for the first nuclear test: Trinity.
Nuclear weapon designs are physical, chemical, and engineering arrangements that cause the physics package[1] of a nuclear weapon to detonate. There are three basic design types. In all three, the explosive energy of deployed devices has been derived primarily from nuclear fission, not fusion.
  • Pure fission weapons were the first nuclear weapons built and have so far been the only type ever used in warfare. The active material is fissile uranium (U-235) or plutonium (Pu-239), explosively assembled into a chain-reacting critical mass by one of two methods:
    • Gun assembly: one piece of fissile uranium is fired at a fissile uranium target at the end of the weapon, similar to firing a bullet down a gun barrel, achieving critical mass when combined.
    • Implosion: a fissile mass of either material (U-235, Pu-239, or a combination) is surrounded by high explosives that compress the mass, resulting in criticality.
The implosion method can use either uranium or plutonium as fuel. The gun method only uses uranium. Plutonium is considered impractical for the gun method because of early triggering due to Pu-240 contamination and due to its time constant for prompt critical fission being much shorter than that of U-235.
  • Fusion-boosted fission weapons improve on the implosion design. The high pressure and temperature environment at the center of an exploding fission weapon compresses and heats a mixture of tritium and deuterium gas (heavy isotopes of hydrogen). The hydrogen fuses to form helium and free neutrons. The energy release from this fusion reaction is relatively negligible, but each neutron starts a new fission chain reaction, speeding up the fission and greatly reducing the amount of fissile material that would otherwise be wasted when expansion of the fissile material stops the chain reaction. Boosting can more than double the weapon's fission energy release.
  • Two-stage thermonuclear weapons are essentially a chain of fission-boosted fusion weapons (not to be confused with the previously mentioned fusion-boosted fission weapons), usually with only two stages in the chain. The second stage, called the "secondary," is imploded by x-ray energy from the first stage, called the "primary." This radiation implosion is much more effective than the high-explosive implosion of the primary. Consequently, the secondary can be many times more powerful than the primary, without being bigger. The secondary can be designed to maximize fusion energy release, but in most designs fusion is employed only to drive or enhance fission, as it is in the primary. More stages could be added, but the result would be a multi-megaton weapon too powerful to serve any plausible purpose.[2] (The United States briefly deployed a three-stage 25-megaton bomb, the B41, starting in 1961. Also in 1961, the Soviet Union tested, but did not deploy, a three-stage 50–100 megaton device, Tsar Bomba.)
Pure fission weapons historically have been the first type to be built by a nation state. Large industrial states with well-developed nuclear arsenals have two-stage thermonuclear weapons, which are the most compact, scalable, and cost effective option once the necessary industrial infrastructure is built.
Most known innovations in nuclear weapon design originated in the United States, although some were later developed independently by other states;[3] the following descriptions feature U.S. designs.
In early news accounts, pure fission weapons were called atomic bombs or A-bombs, a misnomer since the energy comes only from the nucleus of the atom. Weapons involving fusion were called hydrogen bombs or H-bombs, also a misnomer since their destructive energy comes mostly from fission. Insiders favored the terms nuclear and thermonuclear, respectively.
The term thermonuclear refers to the high temperatures required to initiate fusion. It ignores the equally important factor of pressure, which was considered secret at the time the term became current. Many nuclear weapon terms are similarly inaccurate because of their origin in a classified environment.
Nuclear weapons
Fat man.jpg
History
Warfare
Arms race
Design
Testing
Effects
Delivery
Espionage
Proliferation
Arsenals
Terrorism
Anti-nuclear opposition
Nuclear-armed states
United States · Russia
United Kingdom · France
China · India · Israel
Pakistan · North Korea
South Africa (former)
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[edit] Nuclear reactions

Nuclear fission splits heavier atoms to form lighter atoms. Nuclear fusion bonds together lighter atoms to form heavier atoms. Both reactions generate roughly a million times more energy than comparable chemical reactions, making nuclear bombs a million times more powerful than non-nuclear bombs, which a French patent claimed in May 1939.[4]
In some ways, fission and fusion are opposite and complementary reactions, but the particulars are unique for each. To understand how nuclear weapons are designed, it is useful to know the important similarities and differences between fission and fusion. The following explanation uses rounded numbers and approximations.[5]

[edit] Fission

When a free neutron hits the nucleus of a fissionable atom like uranium-235 ( 235U), the uranium splits into two smaller atoms called fission fragments, plus more neutrons. Fission can be self-sustaining because it produces more neutrons of the speed required to cause new fissions.
The uranium atom can split any one of dozens of different ways, as long as the atomic weights add up to 236 (uranium plus the extra neutron). The following equation shows one possible split, namely into strontium-95 ( 95Sr), xenon-139 (139Xe), and two neutrons (n), plus energy:[6]
\ {}^{235}\mathrm{U} + n = {}^{95}\mathrm{Sr} + {}^{139}\mathrm{Xe} + 2n + 180\ \mathrm{MeV}
The immediate energy release per atom is 180 million electron volts (MeV), i.e. 74 TJ/kg, of which 90% is kinetic energy (or motion) of the fission fragments, flying away from each other mutually repelled by the positive charge of their protons (38 for strontium, 54 for xenon). Thus their initial kinetic energy is 67 TJ/kg, hence their initial speed is 12,000 kilometers per second, but their high electric charge causes many inelastic collisions with nearby nuclei. The fragments remain trapped inside the bomb's uranium pit until their motion is converted into x-ray heat, a process which takes about a millionth of a second (a microsecond).
This x-ray energy produces the blast and fire which are normally the purpose of a nuclear explosion.
After the fission products slow down, they remain radioactive. Being new elements with too many neutrons, they eventually become stable by means of beta decay, converting neutrons into protons by throwing off electrons and gamma rays. Each fission product nucleus decays between one and six times, average three times, producing a variety of isotopes of different elements, some stable, some highly radioactive, and others radioactive with half-lives up to 200,000 years.[7] In reactors, the radioactive products are the nuclear waste in spent fuel. In bombs, they become radioactive fallout, both local and global.
Meanwhile, inside the exploding bomb, the free neutrons released by fission strike nearby U-235 nuclei causing them to fission in an exponentially growing chain reaction (1, 2, 4, 8, 16, etc.). Starting from one, the number of fissions can theoretically double a hundred times in a microsecond, which could consume all uranium up to hundreds of tons by the hundredth link in the chain. In practice, bombs do not contain that much uranium, and, anyway, just a few kilograms undergo fission before the uranium blows itself apart.
Holding an exploding bomb together is the greatest challenge of fission weapon design. The heat of fission rapidly expands the uranium pit, spreading apart the target nuclei and making space for the neutrons to escape without being captured. The chain reaction stops.
Materials which can sustain a chain reaction are called fissile. The two fissile materials used in nuclear weapons are: U-235, also known as highly enriched uranium (HEU), oralloy (Oy) meaning Oak Ridge Alloy, or 25 (the last digits of the atomic number, which is 92 for uranium, and the atomic weight, here 235, respectively); and Pu-239, also known as plutonium, or 49 (from 94 and 239).
Uranium's most common isotope, U-238, is fissionable but not fissile (meaning that it cannot sustain a chain reaction by itself but can be made to fission, specifically by neutrons from a fusion reaction). Its aliases include natural or unenriched uranium, depleted uranium (DU), tubealloy (Tu), and 28. It cannot sustain a chain reaction, because its own fission neutrons are not powerful enough to cause more U-238 fission. However, the neutrons released by fusion will fission U-238. This U-238 fission reaction produces most of the destructive energy in a typical two-stage thermonuclear weapon.

[edit] Fusion

Fusion produces neutrons which dissipate energy from the reaction.[8] In weapons, the most important fusion reaction is called the D-T reaction. Using the heat and pressure of fission, hydrogen-2, or deuterium ( 2D), fuses with hydrogen-3, or tritium ( 3T), to form helium-4 ( 4He) plus one neutron (n) and energy:[9]
\ ^2\mathrm{D} + ^3\! \mathrm{T} = ^4\! \!\mathrm{He} + n + 17.6\ \mathrm{MeV}
Deuterium-tritium fusion.svg
Notice that the total energy output, 17.6 MeV, is one tenth of that with fission, but the ingredients are only one-fiftieth as massive, so the energy output per unit mass is greater. However, in this fusion reaction 80% of the energy, or 14 MeV, is in the motion of the neutron which, having no electric charge and being almost as massive as the hydrogen nuclei that created it, can escape the scene without leaving its energy behind to help sustain the reaction – or to generate x-rays for blast and fire.
The only practical way to capture most of the fusion energy is to trap the neutrons inside a massive bottle of heavy material such as lead, uranium, or plutonium. If the 14 MeV neutron is captured by uranium (either type: 235 or 238) or plutonium, the result is fission and the release of 180 MeV of fission energy, multiplying the energy output tenfold.
Fission is thus necessary to start fusion, helps to sustain fusion, and captures and multiplies the energy released in fusion neutrons. In the case of a neutron bomb (see below) the last-mentioned does not apply since the escape of neutrons is the objective.

[edit] Tritium production

A third important nuclear reaction is the one that creates tritium, essential to the type of fusion used in weapons and, incidentally, the most expensive ingredient in any nuclear weapon. Tritium, or hydrogen-3, is made by bombarding lithium-6 ( 6Li) with a neutron (n) to produce helium-4 ( 4He) plus tritium ( 3T) and energy:[9]
\ ^6\mathrm{Li} + n = ^4\!\!\mathrm{He} + ^3\!\mathrm{T} + 5\ \mathrm{MeV}
A nuclear reactor is necessary to provide the neutrons. The industrial-scale conversion of lithium-6 to tritium is very similar to the conversion of uranium-238 into plutonium-239. In both cases the feed material is placed inside a nuclear reactor and removed for processing after a period of time. In the 1950s, when reactor capacity was limited, the production of tritium and plutonium were in direct competition. Every atom of tritium in a weapon replaced an atom of plutonium that could have been produced instead.
The fission of one plutonium atom releases ten times more total energy than the fusion of one tritium atom, and it generates fifty times[citation needed] more blast and fire. For this reason, tritium is included in nuclear weapon components only when it causes more fission than its production sacrifices, namely in the case of fusion-boosted fission.
However, an exploding nuclear bomb is a nuclear reactor. The above reaction can take place simultaneously throughout the secondary of a two-stage thermonuclear weapon, producing tritium in place as the device explodes.
Of the three basic types of nuclear weapon, the first, pure fission, uses the first of the three nuclear reactions above. The second, fusion-boosted fission, uses the first two. The third, two-stage thermonuclear, uses all three.

[edit] Pure fission weapons

The first task of a nuclear weapon design is to rapidly assemble a supercritical mass of fissile uranium or plutonium. A supercritical mass is one in which the percentage of fission-produced neutrons captured by another fissile nucleus is large enough that each fission event, on average, causes more than one additional fission event.
Once the critical mass is assembled, at maximum density, a burst of neutrons is supplied to start as many chain reactions as possible. Early weapons used an "urchin" inside the pit containing polonium-210 and beryllium separated by a thin barrier. Implosion of the pit crushed the urchin, mixing the two metals, thereby allowing alpha particles from the polonium to interact with beryllium to produce free neutrons. In modern weapons, the neutron generator is a high-voltage vacuum tube containing a particle accelerator which bombards a deuterium/tritium-metal hydride target with deuterium and tritium ions. The resulting small-scale fusion produces neutrons at a protected location outside the physics package, from which they penetrate the pit. This method allows better control of the timing of chain reaction initiation.
The critical mass of an uncompressed sphere of bare metal is 110 lb (50 kg) for uranium-235 and 35 lb (16 kg) for delta-phase plutonium-239. In practical applications, the amount of material required for criticallity is modified by shape, purity, density, and the proximity to neutron-reflecting material, all of which affect the escape or capture of neutrons.
To avoid a chain reaction during handling, the fissile material in the weapon must be sub-critical before detonation. It may consist of one or more components containing less than one uncompressed critical mass each. A thin hollow shell can have more than the bare-sphere critical mass, as can a cylinder, which can be arbitrarily long without ever reaching criticallity.
A tamper is an optional layer of dense material surrounding the fissile material. Due to its inertia it delays the expansion of the reacting material, increasing the efficiency of the weapon. Often the same layer serves both as tamper and as neutron reflector.

[edit] Gun-type assembly weapon

Diagram of a gun-type fission weapon
Little Boy, the Hiroshima bomb, used 141 lb (64 kg) of uranium with an average enrichment of around 80%, or 112 lb (51 kg) of U-235, just about the bare-metal critical mass. (See Little Boy article for a detailed drawing.) When assembled inside its tamper/reflector of tungsten carbide, the 141 lb (64 kg) was more than twice critical mass. Before the detonation, the uranium-235 was formed into two sub-critical pieces, one of which was later fired down a gun barrel to join the other, starting the atomic explosion. About 1% of the uranium underwent fission;[10] the remainder, representing most of the entire wartime output of the giant factories at Oak Ridge, scattered uselessly.[11] The half life of uranium-235 is 704 million years.
The inefficiency was caused by the speed with which the uncompressed fissioning uranium expanded and became sub-critical by virtue of decreased density. Despite its inefficiency, this design, because of its shape, was adapted for use in small-diameter, cylindrical artillery shells (a gun-type warhead fired from the barrel of a much larger gun). Such warheads were deployed by the United States until 1992, accounting for a significant fraction of the U-235 in the arsenal, and were some of the first weapons dismantled to comply with treaties limiting warhead numbers. The rationale for this decision was undoubtedly a combination of the lower yield and grave safety issues associated with the gun-type design.

[edit] Implosion-type weapon

Implosion Nuclear weapon.svg
Fat Man, the Nagasaki bomb, used 13.6 lb (6.2 kg, about 12 fluid ounces or 350 ml in volume) of Pu-239, which is only 39% of bare-sphere critical mass. (See Fat Man article for a detailed drawing.) Surrounded by a U-238 reflector/tamper, the pit was brought close to critical mass by the neutron-reflecting properties of the U-238. During detonation, criticality was achieved by implosion. The plutonium pit was squeezed to increase its density by simultaneous detonation of the conventional explosives placed uniformly around the pit. The explosives were detonated by multiple exploding-bridgewire detonators. It is estimated that only about 20% of the plutonium underwent fission; the rest, about 11 lb (5.0 kg), was scattered.
Implosion bomb animated.gif
An implosion shock wave might be of such short duration that only a fraction of the pit is compressed at any instant as the wave passes through it.
Flash X-Ray images of the converging shock waves formed during a test of the high explosive lens system.
A pusher shell made out of low density metal—such as aluminum, beryllium, or an alloy of the two metals (aluminum being easier and safer to shape, and is two orders of magnitude cheaper; beryllium for its high-neutron-reflective capability) —may be needed. The pusher is located between the explosive lens and the tamper. It works by reflecting some of the shock wave backwards, thereby having the effect of lengthening its duration. Fat Man used an aluminum pusher.
The key to Fat Man's greater efficiency was the inward momentum of the massive U-238 tamper (which did not undergo fission). Once the chain reaction started in the plutonium, the momentum of the implosion had to be reversed before expansion could stop the fission. By holding everything together for a few hundred nanoseconds more, the efficiency was increased.

[edit] Plutonium pit

The core of an implosion weapon – the fissile material and any reflector or tamper bonded to it – is known as the pit. Some weapons tested during the 1950s used pits made with U-235 alone, or in composite with plutonium,[12] but all-plutonium pits are the smallest in diameter and have been the standard since the early 1960s.
Casting and then machining plutonium is difficult not only because of its toxicity, but also because plutonium has many different metallic phases, also known as allotropes. As plutonium cools, changes in phase result in distortion and cracking. This distortion is normally overcome by alloying it with 3–3.5 molar% (0.9–1.0% by weight) gallium, forming a plutonium-gallium alloy, which causes it to take up its delta phase over a wide temperature range.[13] When cooling from molten it then suffers only a single phase change, from epsilon to delta, instead of the four changes it would otherwise pass through. Other trivalent metals would also work, but gallium has a small neutron absorption cross section and helps protect the plutonium against corrosion. A drawback is that gallium compounds themselves are corrosive and so if the plutonium is recovered from dismantled weapons for conversion to plutonium dioxide for power reactors, there is the difficulty of removing the gallium.
Because plutonium is chemically reactive it is common to plate the completed pit with a thin layer of inert metal, which also reduces the toxic hazard.[14] The gadget used galvanic silver plating; afterwards, nickel deposited from nickel tetracarbonyl vapors was used,[14] but gold is now preferred.[citation needed]

[edit] Levitated-pit implosion

The first improvement on the Fat Man design was to put an air space between the tamper and the pit to create a hammer-on-nail impact. The pit, supported on a hollow cone inside the tamper cavity, was said to be levitated. The three tests of Operation Sandstone, in 1948, used Fat Man designs with levitated pits. The largest yield was 49 kilotons, more than twice the yield of the unlevitated Fat Man.[15]
It was immediately clear that implosion was the best design for a fission weapon. Its only drawback seemed to be its diameter. Fat Man was 5 feet (1.5 m) wide vs 2 feet (60 cm) for Little Boy.
Eleven years later, implosion designs had advanced sufficiently that the 5-foot (1.5 m)-diameter sphere of Fat Man had been reduced to a 1-foot (0.30 m)-diameter cylinder 2 feet (0.61 m) long, the Swan device.
The Pu-239 pit of Fat Man was only 3.6 inches (9 cm) in diameter, the size of a softball. The bulk of Fat Man's girth was the implosion mechanism, namely concentric layers of U-238, aluminum, and high explosives. The key to reducing that girth was the two-point implosion design.

[edit] Two-point linear implosion

Linear implosion schematic.svg
A very inefficient implosion design is one that simply reshapes an ovoid into a sphere, with minimal compression. In linear implosion, an untamped, solid, elongated mass of Pu-239, larger than critical mass in a sphere, is embedded inside a cylinder of high explosive with a detonator at each end.[16]
Detonation makes the pit critical by driving the ends inward, creating a spherical shape. The shock may also change plutonium from delta to alpha phase, increasing its density by 23%, but without the inward momentum of a true implosion. The lack of compression makes it inefficient, but the simplicity and small diameter make it suitable for use in artillery shells and atomic demolition munitions – ADMs – also known as backpack or suitcase nukes.
All such low-yield battlefield weapons, whether gun-type U-235 designs or linear implosion Pu-239 designs, pay a high price in fissile material in order to achieve diameters between six and ten inches (254 mm).

[edit] Two-point hollow-pit implosion

A more efficient two-point implosion system uses two high explosive lenses and a hollow pit.
A hollow plutonium pit was the original plan for the 1945 Fat Man bomb, but there was not enough time to develop and test the implosion system for it. A simpler solid-pit design was considered more reliable, given the time restraint, but it required a heavy U-238 tamper, a thick aluminum pusher, and three tons of high explosives.
After the war, interest in the hollow pit design was revived. Its obvious advantage is that a hollow shell of plutonium, shock-deformed and driven inward toward its empty center, would carry momentum into its violent assembly as a solid sphere. It would be self-tamping, requiring a smaller U-238 tamper, no aluminum pusher and less high explosive.
The Fat Man bomb had two concentric, spherical shells of high explosives, each about 10 inches (25 cm) thick. The inner shell drove the implosion. The outer shell consisted of a soccer-ball pattern of 32 high explosive lenses, each of which converted the convex wave from its detonator into a concave wave matching the contour of the outer surface of the inner shell. If these 32 lenses could be replaced with only two, the high explosive sphere could become an ellipsoid (prolate spheroid) with a much smaller diameter.
A good illustration of these two features is a 1956 drawing from the Swedish nuclear weapon program (which was terminated before it produced a test explosion). The drawing shows the essential elements of the two-point hollow-pit design.
Swedish Atomic Bomb.png
There are similar drawings in the open literature that come from the post-war German nuclear bomb program, which was also terminated, and from the French program, which produced an arsenal.
The mechanism of the high explosive lens (diagram item #6) is not shown in the Swedish drawing, but a standard lens made of fast and slow high explosives, as in Fat Man, would be much longer than the shape depicted. For a single high explosive lens to generate a concave wave that envelops an entire hemisphere, it must either be very long or the part of the wave on a direct line from the detonator to the pit must be slowed dramatically.
A slow high explosive is too fast, but the flying plate of an "air lens" is not. A metal plate, shock-deformed, and pushed across an empty space can be designed to move slowly enough.[17][18] A two-point implosion system using air lens technology can have a length no more than twice its diameter, as in the Swedish diagram above.

[edit] Fusion-boosted fission weapons

The next step in miniaturization was to speed up the fissioning of the pit to reduce the minimum inertial confinement time. The hollow pit provided an ideal location to introduce fusion for the boosting of fission. A 50–50 mixture of tritium and deuterium gas, pumped into the pit during arming, will fuse into helium and release free neutrons soon after fission begins. The neutrons will start a large number of new chain reactions while the pit is still critical or nearly critical.
Once the hollow pit is perfected, there is little reason not to boost.
The concept of fusion-boosted fission was first tested on May 25, 1951, in the Item shot of Operation Greenhouse, Eniwetok, yield 45.5 kilotons.
Boosting reduces diameter in three ways, all the result of faster fission:
  • Since the compressed pit does not need to be held together as long, the massive U-238 tamper can be replaced by a light-weight beryllium shell (to reflect escaping neutrons back into the pit). The diameter is reduced.
  • The mass of the pit can be reduced by half, without reducing yield. Diameter is reduced again.
  • Since the mass of the metal being imploded (tamper plus pit) is reduced, a smaller charge of high explosive is needed, reducing diameter even further.
Since boosting is required to attain full design yield, any reduction in boosting reduces yield. Boosted weapons are thus variable-yield weapons. Yield can be reduced any time before detonation, simply by putting less than the full amount of tritium into the pit during the arming procedure.
U.S. Swan Device.svg
The first device whose dimensions suggest employment of all these features (two-point, hollow-pit, fusion-boosted implosion) was the Swan device, tested June 22, 1956, as the Inca shot of Operation Redwing, at Eniwetok. Its yield was 15 kilotons, about the same as Little Boy, the Hiroshima bomb. It weighed 105 lb (47.6 kg) and was cylindrical in shape, 11.6 inches (29.5 cm) in diameter and 22.9 inches (58 cm) long. The above schematic illustrates what were probably its essential features.
Eleven days later, July 3, 1956, the Swan was test-fired again at Eniwetok, as the Mohawk shot of Redwing. This time it served as the primary, or first stage, of a two-stage thermonuclear device, a role it played in a dozen such tests during the 1950s. Swan was the first off-the-shelf, multi-use primary, and the prototype for all that followed.
Nuclear Weapon Miniaturization.png
After the success of Swan, 11 or 12 inches (300 mm) seemed to become the standard diameter of boosted single-stage devices tested during the 1950s. Length was usually twice the diameter, but one such device, which became the W54 warhead, was closer to a sphere, only 15 inches (380 mm) long. It was tested two dozen times in the 1957–62 period before being deployed. No other design had such a long string of test failures. Since the longer devices tended to work correctly on the first try, there must have been some difficulty in flattening the two high explosive lenses enough to achieve the desired length-to-width ratio.
One of the applications of the W54 was the Davy Crockett XM-388 recoilless rifle projectile, shown here in comparison to its Fat Man predecessor, dimensions in inches.
Another benefit of boosting, in addition to making weapons smaller, lighter, and with less fissile material for a given yield, is that it renders weapons immune to radiation interference (RI). It was discovered in the mid-1950s that plutonium pits would be particularly susceptible to partial predetonation if exposed to the intense radiation of a nearby nuclear explosion (electronics might also be damaged, but this was a separate issue). RI was a particular problem before effective early warning radar systems because a first strike attack might make retaliatory weapons useless. Boosting reduces the amount of plutonium needed in a weapon to below the quantity which would be vulnerable to this effect.

[edit] Two-stage thermonuclear weapons

Pure fission or fusion-boosted fission weapons can be made to yield hundreds of kilotons, at great expense in fissile material and tritium, but by far the most efficient way to increase nuclear weapon yield beyond ten or so kilotons is to tack on a second independent stage, called a secondary.
Ivy Mike, the first two-stage thermonuclear detonation, 10.4 megatons, November 1, 1952.
In the 1940s, bomb designers at Los Alamos thought the secondary would be a canister of deuterium in liquified or hydride form. The fusion reaction would be D-D, harder to achieve than D-T, but more affordable. A fission bomb at one end would shock-compress and heat the near end, and fusion would propagate through the canister to the far end. Mathematical simulations showed it wouldn't work, even with large amounts of prohibitively expensive tritium added in.
The entire fusion fuel canister would need to be enveloped by fission energy, to both compress and heat it, as with the booster charge in a boosted primary. The design breakthrough came in January 1951, when Edward Teller and StanisÅ‚aw Ulam invented radiation implosion—for nearly three decades known publicly only as the Teller-Ulam H-bomb secret.
The concept of radiation implosion was first tested on May 9, 1951, in the George shot of Operation Greenhouse, Eniwetok, yield 225 kilotons. The first full test was on November 1, 1952, the Mike shot of Operation Ivy, Eniwetok, yield 10.4 megatons.
In radiation implosion, the burst of X-ray energy coming from an exploding primary is captured and contained within an opaque-walled radiation channel which surrounds the nuclear energy components of the secondary. The radiation quickly turns the plastic foam that had been filling the channel into a plasma which is mostly transparent to X-rays, and the radiation is absorbed in the outermost layers of the pusher/tamper surrounding the secondary, which ablates and applies a massive force[19] (much like an inside out rocket engine) causing the fusion fuel capsule to implode much like the pit of the primary. As the secondary implodes a fissile "spark plug" at its center ignites and provides heat which enables the fusion fuel to ignite as well. The fission and fusion chain reactions exchange neutrons with each other and boost the efficiency of both reactions. The greater implosive force, enhanced efficiency of the fissile "spark plug" due to boosting via fusion neutrons, and the fusion explosion itself provides significantly greater explosive yield from the secondary despite often not being much larger than the primary.
A Warhead before firing; primary at top, secondary at bottom. Both components are fusion-boosted fission bombs. B High-explosive fires in primary, compressing plutonium core into supercriticality and beginning a fission reaction. C Fission in primary emits X-rays which channel along the inside of the casing, irradiating the polystyrene foam channel filler. D Secondary compressed by X-ray induced ablation, and Plutonium sparkplug inside the secondary begins to fission, supplying heat. E Compressed and heated, lithium-6 deuteride fuel begins fusion reaction, neutron flux causes tamper to fission. A fireball is starting to form...
For example, for the Redwing Mohawk test on July 3, 1956, a secondary called the Flute was attached to the Swan primary. The Flute was 15 inches (38 cm) in diameter and 23.4 inches (59 cm) long, about the size of the Swan. But it weighed ten times as much and yielded 24 times as much energy (355 kilotons, vs 15 kilotons).
Equally important, the active ingredients in the Flute probably cost no more than those in the Swan. Most of the fission came from cheap U-238, and the tritium was manufactured in place during the explosion. Only the spark plug at the axis of the secondary needed to be fissile.
A spherical secondary can achieve higher implosion densities than a cylindrical secondary, because spherical implosion pushes in from all directions toward the same spot. However, in warheads yielding more than one megaton, the diameter of a spherical secondary would be too large for most applications. A cylindrical secondary is necessary in such cases. The small, cone-shaped re-entry vehicles in multiple-warhead ballistic missiles after 1970 tended to have warheads with spherical secondaries, and yields of a few hundred kilotons.
As with boosting, the advantages of the two-stage thermonuclear design are so great that there is little incentive not to use it, once a nation has mastered the technology.
In engineering terms, radiation implosion allows for the exploitation of several known features of nuclear bomb materials which heretofore had eluded practical application. For example:
  • The best way to store deuterium in a reasonably dense state is to chemically bond it with lithium, as lithium deuteride. But the lithium-6 isotope is also the raw material for tritium production, and an exploding bomb is a nuclear reactor. Radiation implosion will hold everything together long enough to permit the complete conversion of lithium-6 into tritium, while the bomb explodes. So the bonding agent for deuterium permits use of the D-T fusion reaction without any pre-manufactured tritium being stored in the secondary. The tritium production constraint disappears.
  • For the secondary to be imploded by the hot, radiation-induced plasma surrounding it, it must remain cool for the first microsecond, i.e., it must be encased in a massive radiation (heat) shield. The shield's massiveness allows it to double as a tamper, adding momentum and duration to the implosion. No material is better suited for both of these jobs than ordinary, cheap uranium-238, which also happens to undergo fission when struck by the neutrons produced by D-T fusion. This casing, called the pusher, thus has three jobs: to keep the secondary cool, to hold it, inertially, in a highly compressed state, and, finally, to serve as the chief energy source for the entire bomb. The consumable pusher makes the bomb more a uranium fission bomb than a hydrogen fusion bomb. It is noteworthy that insiders never used the term hydrogen bomb.[20]
  • Finally, the heat for fusion ignition comes not from the primary but from a second fission bomb called the spark plug, embedded in the heart of the secondary. The implosion of the secondary implodes this spark plug, detonating it and igniting fusion in the material around it, but the spark plug then continues to fission in the neutron-rich environment until it is fully consumed, adding significantly to the yield.[21]
The initial impetus behind the two-stage weapon was President Truman's 1950 promise to build a 10-megaton hydrogen superbomb as the U.S. response to the 1949 test of the first Soviet fission bomb. But the resulting invention turned out to be the cheapest and most compact way to build small nuclear bombs as well as large ones, erasing any meaningful distinction between A-bombs and H-bombs, and between boosters and supers. All the best techniques for fission and fusion explosions are incorporated into one all-encompassing, fully scalable design principle. Even six-inch (152 mm) diameter nuclear artillery shells can be two-stage thermonuclears.
In the ensuing fifty years, nobody has come up with a better way to build a nuclear bomb. It is the design of choice for the United States, Russia, the United Kingdom, China, and France, the five thermonuclear powers. The other nuclear-armed nations, Israel, India, Pakistan, and North Korea, probably have single-stage weapons, possibly boosted.[21]

[edit] Interstage

In a two-stage thermonuclear weapon the energy from the primary impacts the secondary. An essential energy transfer modulator called the interstage, between the primary and the secondary, protects the secondary's fusion fuel from heating too quickly, which could cause it to explode in a conventional (and small) heat explosion before the fission and fusion reactions get a chance to start.
There is very little information in the open literature about the mechanism of the interstage. Its first mention in a U.S. government document formally released to the public appears to be a caption in a recent graphic promoting the Reliable Replacement Warhead Program. If built, this new design would replace "toxic, brittle material" and "expensive 'special' material" in the interstage.[22] This statement suggests the interstage may contain beryllium to moderate the flux of neutrons from the primary, and perhaps something to absorb and re-radiate the x-rays in a particular manner.[23] There is also some speculation that this interstage material, which may be code-named FOGBANK might be an aerogel, possibly doped with beryllium and/or other substances.[24]
The interstage and the secondary are encased together inside a stainless steel membrane to form the canned subassembly (CSA), an arrangement which has never been depicted in any open-source drawing.[25] The most detailed illustration of an interstage shows a British thermonuclear weapon with a cluster of items between its primary and a cylindrical secondary. They are labeled "end-cap and neutron focus lens," "reflector/neutron gun carriage," and "reflector wrap." The origin of the drawing, posted on the internet by Greenpeace, is uncertain, and there is no accompanying explanation.[26]

[edit] Specific designs

While every nuclear weapon design falls into one of the above categories, specific designs have occasionally become the subject of news accounts and public discussion, often with incorrect descriptions about how they work and what they do. Examples:

[edit] Hydrogen bombs

All modern nuclear weapons make some use of D-T fusion. Even pure fission weapons include neutron generators which are high-voltage vacuum tubes containing trace amounts of tritium and deuterium.
However, in the public perception, hydrogen bombs, or H-bombs, are multi-megaton devices a thousand times more powerful than Hiroshima's Little Boy. Such high-yield bombs are actually two-stage thermonuclears, scaled up to the desired yield, with uranium fission, as usual, providing most of their energy.
The idea of the hydrogen bomb first came to public attention in 1949, when prominent scientists openly recommended against building nuclear bombs more powerful than the standard pure-fission model, on both moral and practical grounds. Their assumption was that critical mass considerations would limit the potential size of fission explosions, but that a fusion explosion could be as large as its supply of fuel, which has no critical mass limit. In 1949, the Soviets exploded their first fission bomb, and in 1950 President Truman ended the H-bomb debate by ordering the Los Alamos designers to build one.
In 1952, the 10.4-megaton Ivy Mike explosion was announced as the first hydrogen bomb test, reinforcing the idea that hydrogen bombs are a thousand times more powerful than fission bombs.
In 1954, J. Robert Oppenheimer was labeled a hydrogen bomb opponent. The public did not know there were two kinds of hydrogen bomb (neither of which is accurately described as a hydrogen bomb). On May 23, when his security clearance was revoked, item three of the four public findings against him was "his conduct in the hydrogen bomb program." In 1949, Oppenheimer had supported single-stage fusion-boosted fission bombs, to maximize the explosive power of the arsenal given the trade-off between plutonium and tritium production. He opposed two-stage thermonuclear bombs until 1951, when radiation implosion, which he called "technically sweet", first made them practical. The complexity of his position was not revealed to the public until 1976, nine years after his death.[27]
When ballistic missiles replaced bombers in the 1960s, most multi-megaton bombs were replaced by missile warheads (also two-stage thermonuclears) scaled down to one megaton or less.

[edit] Alarm Clock/Sloika

The first effort to exploit the symbiotic relationship between fission and fusion was a 1940s design that mixed fission and fusion fuel in alternating thin layers. As a single-stage device, it would have been a cumbersome application of boosted fission. It first became practical when incorporated into the secondary of a two-stage thermonuclear weapon.[28]
The U.S. name, Alarm Clock, was a nonsense code name. The Russian name for the same design was more descriptive: Sloika (Russian: Слойка), a layered pastry cake. A single-stage Soviet Sloika was tested on August 12, 1953. No single-stage U.S. version was tested, but the Union shot of Operation Castle, April 26, 1954, was a two-stage thermonuclear code-named Alarm Clock. Its yield, at Bikini, was 6.9 megatons.
Because the Soviet Sloika test used dry lithium-6 deuteride eight months before the first U.S. test to use it (Castle Bravo, March 1, 1954), it was sometimes claimed that the USSR won the H-bomb race. (The 1952 U.S. Ivy Mike test used cryogenically cooled liquid deuterium as the fusion fuel in the secondary, and employed the D-D fusion reaction.) However, the first Soviet test to use a radiation-imploded secondary, the essential feature of a true H-bomb, was on November 23, 1955, three years after Ivy Mike.

[edit] Clean bombs

Bassoon, the prototype for a 3.5-megaton clean bomb or a 25-megaton dirty bomb. Dirty version shown here, before its 1956 test.
On March 1, 1954, the largest-ever U.S. nuclear test explosion, the 15-megaton Bravo shot of Operation Castle at Bikini, delivered a promptly lethal dose of fission-product fallout to more than 6,000 square miles (16,000 km2) of Pacific Ocean surface.[29] Radiation injuries to Marshall Islanders and Japanese fishermen made that fact public and revealed the role of fission in hydrogen bombs.
In response to the public alarm over fallout, an effort was made to design a clean multi-megaton weapon, relying almost entirely on fusion. Since the energy produced by the fissioning of unenriched natural Uranium when utilized as the tamper material in the Secondary and subsequent stages in the Teller-Ulam design, can evidently dwarf the Fusion yield output, as was the case in the Castle bravo test, and realising that a non fissionable tamper material is an essential requirement in a 'clean' bomb, it is clear that in such a 'clean' bomb there will now be a relatively massive amount of material that does not undergo any mass-to-energy conversions whatsoever, So for a given weight, 'dirty' weapons with Fissionable tampers are much lighter than a 'clean' weapon of equal yield. The earliest known incidence of a three-stage device being tested, with the third stage, called the tertiary, being ignited by the secondary, was May 27, 1956 in the Bassoon device. This device was tested in the Zuni shot of Operation Redwing. This shot utilized non fissionable tampers, a relatively nuclear inert substitute material such as tungsten or lead was used, its yield was 3.5 megatons, 85% fusion and only 15% fission. The public records for devices that produced the highest proportion of their yield via fusion-only reactions are the 57 megaton, Tsar bomba at 97% Fusion,[30] the 9.3 megaton Hardtack Poplar test at 95.2%,[31] and the 4.5 megaton Redwing Navajo test at 95% fusion.[32]
On July 19 1956, AEC Chairman Lewis Strauss said that the Redwing Zuni shot clean bomb test "produced much of importance ... from a humanitarian aspect." However, less than two days after this announcement the dirty version of Bassoon, called Bassoon Prime, with a uranium-238 tamper in place, was tested on a barge off the coast of Bikini Atoll as the Redwing Tewa shot. The Bassoon Prime produced a 5-megaton yield, of which 87% came from fission. Data obtained from this test, and others culminated in the eventual deployment of the highest yielding US nuclear weapon known, and as a side, the highest Yield-to-weight weapon ever made a three-stage thermonuclear weapon, with a maximum 'dirty' yield of 25-megatons designated as the Mark-41 bomb, which was to be carried by U.S. Air Force bombers until it was decommissioned, this weapon was never fully tested.
As such, high-yield clean bombs appear to have been a public relations exercise. The actual deployed weapons were the dirty versions, which maximized yield for the same size device. However Newer 4th and 5th Generation nuclear weapons designs including Pure fusion weapon and antimatter catalyzed nuclear pulse propulsion like devices[33] are being studied extensively by the 5 largest nuclear weapon states.[34][35]

[edit] Cobalt bombs

A fictional doomsday bomb, made popular by Nevil Shute's 1957 novel, and subsequent 1959 movie, On the Beach, the cobalt bomb was a hydrogen bomb with a jacket of cobalt metal. The neutron-activated cobalt would supposedly have maximized the environmental damage from radioactive fallout. These bombs were popularized in the 1964 film Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb. The element added to the bombs is referred to in the film as 'cobalt-thorium G'
Such "salted" weapons were requested by the U.S. Air Force and seriously investigated, possibly built and tested, but not deployed. In the 1964 edition of the DOD/AEC book The Effects of Nuclear Weapons, a new section titled Radiological Warfare clarified the issue.[36] Fission products are as deadly as neutron-activated cobalt. The standard high-fission thermonuclear weapon is automatically a weapon of radiological warfare, as dirty as a cobalt bomb.
Initially, gamma radiation from the fission products of an equivalent size fission-fusion-fission bomb are much more intense than Co-60: 15,000 times more intense at 1 hour; 35 times more intense at 1 week; 5 times more intense at 1 month; and about equal at 6 months. Thereafter fission drops off rapidly so that Co-60 fallout is 8 times more intense than fission at 1 year and 150 times more intense at 5 years. The very long-lived isotopes produced by fission would overtake the 60Co again after about 75 years.[37]

[edit] Fission-fusion-fission bombs

In 1954, to explain the surprising amount of fission-product fallout produced by hydrogen bombs, Ralph Lapp coined the term fission-fusion-fission to describe a process inside what he called a three-stage thermonuclear weapon. His process explanation was correct, but his choice of terms caused confusion in the open literature. The stages of a nuclear weapon are not fission, fusion, and fission. They are the primary, the secondary, and, in one exceptionally powerful weapon, the tertiary. Each of these stages employs fission, fusion, and fission.

[edit] Neutron bombs

A neutron bomb, technically referred to as an enhanced radiation weapon (ERW), is a type of tactical nuclear weapon designed specifically to release a large portion of its energy as energetic neutron radiation. This contrasts with standard thermonuclear weapons, which are designed to capture this intense neutron radiation to increase its overall explosive yield. In terms of yield, ERWs typically produce about one-tenth that of a fission-type atomic weapon. Even with their significantly lower explosive power, ERWs are still capable of much greater destruction than any conventional bomb. Meanwhile, relative to other nuclear weapons, damage is more focused on biological material than on material infrastructure (though extreme blast and heat effects are not eliminated).
Officially known as enhanced radiation weapons, ERWs, they are more accurately described as suppressed yield weapons. When the yield of a nuclear weapon is less than one kiloton, its lethal radius from blast, 700 m (2300 ft), is less than that from its neutron radiation. However, the blast is more than potent enough to destroy most structures, which are less resistant to blast effects than even unprotected human beings. Blast pressures of upwards of 20 PSI are survivable, whereas most buildings will collapse with a pressure of only 5 PSI.
Commonly misconceived as a weapon designed to kill populations and leave infrastructure intact, these bombs (as mentioned above) are still very capable of leveling buildings over a large radius. The intent of their design was to kill tank crews – tanks giving excellent protection against blast and heat, surviving (relatively) very close to a detonation. And with the Soviets' vast tank battalions during the Cold War, this was the perfect weapon to counter them. The neutron radiation could instantly incapacitate a tank crew out to roughly the same distance that the heat and blast would incapacitate an unprotected human (depending on design). The tank chassis would also be rendered highly radioactive (temporarily) preventing its re-use by a fresh crew.
Neutron weapons were also intended for use in other applications, however. For example, they are effective in anti-nuclear defenses – the neutron flux being capable of neutralising an incoming warhead at a greater range than heat or blast. Nuclear warheads are very resistant to physical damage, but are very difficult to harden against extreme neutron flux.
Energy distribution of weapon

Standard Enhanced
Blast 50% 40%
Thermal energy 35% 25%
Instant radiation 5% 30%
Residual radiation 10% 5%
ERWs were two-stage thermonuclears with all non-essential uranium removed to minimize fission yield. Fusion provided the neutrons. Developed in the 1950s, they were first deployed in the 1970s, by U.S. forces in Europe. The last ones were retired in the 1990s.
A neutron bomb is only feasible if the yield is sufficiently high that efficient fusion stage ignition is possible, and if the yield is low enough that the case thickness will not absorb too many neutrons. This means that neutron bombs have a yield range of 1–10 kilotons, with fission proportion varying from 50% at 1-kiloton to 25% at 10-kilotons (all of which comes from the primary stage). The neutron output per kiloton is then 10–15 times greater than for a pure fission implosion weapon or for a strategic warhead like a W87 or W88.[38]

[edit] Oralloy thermonuclear warheads

In 1999, nuclear weapon design was in the news again, for the first time in decades. In January, the U.S. House of Representatives released the Cox Report (Christopher Cox R-CA) which alleged that China had somehow acquired classified information about the U.S. W88 warhead. Nine months later, Wen Ho Lee, a Taiwanese immigrant working at Los Alamos, was publicly accused of spying, arrested, and served nine months in pre-trial detention, before the case against him was dismissed. It is not clear that there was, in fact, any espionage.
In the course of eighteen months of news coverage, the W88 warhead was described in unusual detail. The New York Times printed a schematic diagram on its front page.[39] The most detailed drawing appeared in A Convenient Spy, the 2001 book on the Wen Ho Lee case by Dan Stober and Ian Hoffman, adapted and shown here with permission.
W-88 warhead detail.png
Designed for use on Trident II (D-5) submarine-launched ballistic missiles, the W88 entered service in 1990 and was the last warhead designed for the U.S. arsenal. It has been described as the most advanced, although open literature accounts do not indicate any major design features that were not available to U.S. designers in 1958.
The above diagram shows all the standard features of ballistic missile warheads since the 1960s, with two exceptions that give it a higher yield for its size.
  • The outer layer of the secondary, called the "pusher", which serves three functions: heat shield, tamper, and fission fuel, is made of U-235 instead of U-238, hence the name Oralloy (U-235) Thermonuclear. Being fissile, rather than merely fissionable, allows the pusher to fission faster and more completely, increasing yield. This feature is available only to nations with a great wealth of fissile uranium. The United States is estimated to have 500 tons.[citation needed]
  • The secondary is located in the wide end of the re-entry cone, where it can be larger, and thus more powerful. The usual arrangement is to put the heavier, denser secondary in the narrow end for greater aerodynamic stability during re-entry from outer space, and to allow more room for a bulky primary in the wider part of the cone. (The W87 warhead drawing in the previous section[clarification needed] shows the usual arrangement.) Because of this new geometry, the W88 primary uses compact conventional high explosives (CHE) to save space,[40] rather than the more usual, and bulky but safer, insensitive high explosives (IHE). The re-entry cone probably has ballast in the nose for aerodynamic stability.[41]
The alternating layers of fission and fusion material in the secondary are an application of the Alarm Clock/Sloika principle.

[edit] Reliable replacement warhead

The United States has not produced any nuclear warheads since 1989, when the Rocky Flats pit production plant, near Boulder, Colorado, was shut down for environmental reasons. With the end of the Cold War two years later, the production line was idled except for inspection and maintenance functions.
The National Nuclear Security Administration, the latest successor for nuclear weapons to the Atomic Energy Commission and the Department of Energy, has proposed building a new pit facility and starting the production line for a new warhead called the Reliable Replacement Warhead (RRW).[42] Two advertised safety improvements of the RRW would be a return to the use of "insensitive high explosives which are far less susceptible to accidental detonation", and the elimination of "certain hazardous materials, such as beryllium, that are harmful to people and the environment."[43] Since the new warhead must not require any nuclear testing, it could not use a new design with untested concepts.

[edit] Weapon design laboratories

All the nuclear weapon design innovations discussed in this article originated from the following three labs in the manner described. Other nuclear weapon design labs in other countries duplicated those design innovations independently, reverse-engineered them from fallout analysis, or acquired them by espionage.[44]

[edit] Berkeley

The first systematic exploration of nuclear weapon design concepts took place in mid-1942 at the University of California, Berkeley. Important early discoveries had been made at the adjacent Lawrence Berkeley Laboratory, such as the 1940 cyclotron-made production and isolation of plutonium. A Berkeley professor, J. Robert Oppenheimer, had just been hired to run the nation's secret bomb design effort. His first act was to convene the 1942 summer conference.
By the time he moved his operation to the new secret town of Los Alamos, New Mexico, in the spring of 1943, the accumulated wisdom on nuclear weapon design consisted of five lectures by Berkeley professor Robert Serber, transcribed and distributed as the Los Alamos Primer. The Primer addressed fission energy, neutron production and capture, nuclear chain reactions, critical mass, tampers, predetonation, and three methods of assembling a bomb: gun assembly, implosion, and "autocatalytic methods," the one approach that turned out to be a dead end.

[edit] Los Alamos

At Los Alamos, it was found in April 1944 by Emilio G. Segrè that the proposed Thin Man Gun assembly type bomb would not work for plutonium because of predetonation problems caused by Pu-240 impurities. So Fat Man, the implosion-type bomb, was given high priority as the only option for plutonium. The Berkeley discussions had generated theoretical estimates of critical mass, but nothing precise. The main wartime job at Los Alamos was the experimental determination of critical mass, which had to wait until sufficient amounts of fissile material arrived from the production plants: uranium from Oak Ridge, Tennessee, and plutonium from the Hanford site in Washington.
In 1945, using the results of critical mass experiments, Los Alamos technicians fabricated and assembled components for four bombs: the Trinity Gadget, Little Boy, Fat Man, and an unused spare Fat Man. After the war, those who could, including Oppenheimer, returned to university teaching positions. Those who remained worked on levitated and hollow pits and conducted weapon effects tests such as Crossroads Able and Baker at Bikini Atoll in 1946.
All of the essential ideas for incorporating fusion into nuclear weapons originated at Los Alamos between 1946 and 1952. After the Teller-Ulam radiation implosion breakthrough of 1951, the technical implications and possibilities were fully explored, but ideas not directly relevant to making the largest possible bombs for long-range Air Force bombers were shelved.
Because of Oppenheimer's initial position in the H-bomb debate, in opposition to large thermonuclear weapons, and the assumption that he still had influence over Los Alamos despite his departure, political allies of Edward Teller decided he needed his own laboratory in order to pursue H-bombs. By the time it was opened in 1952, in Livermore, California, Los Alamos had finished the job Livermore was designed to do.

[edit] Livermore

With its original mission no longer available, the Livermore lab tried radical new designs, that failed. Its first three nuclear tests were fizzles: in 1953, two single-stage fission devices with uranium hydride pits, and in 1954, a two-stage thermonuclear device in which the secondary heated up prematurely, too fast for radiation implosion to work properly.
Shifting gears, Livermore settled for taking ideas Los Alamos had shelved and developing them for the Army and Navy. This led Livermore to specialize in small-diameter tactical weapons, particularly ones using two-point implosion systems, such as the Swan. Small-diameter tactical weapons became primaries for small-diameter secondaries. Around 1960, when the superpower arms race became a ballistic missile race, Livermore warheads were more useful than the large, heavy Los Alamos warheads. Los Alamos warheads were used on the first intermediate-range ballistic missiles, IRBMs, but smaller Livermore warheads were used on the first intercontinental ballistic missiles, ICBMs, and submarine-launched ballistic missiles, SLBMs, as well as on the first multiple warhead systems on such missiles.[45]
In 1957 and 1958 both labs built and tested as many designs as possible, in anticipation that a planned 1958 test ban might become permanent. By the time testing resumed in 1961 the two labs had become duplicates of each other, and design jobs were assigned more on workload considerations than lab specialty. Some designs were horse-traded. For example, the W38 warhead for the Titan I missile started out as a Livermore project, was given to Los Alamos when it became the Atlas missile warhead, and in 1959 was given back to Livermore, in trade for the W54 Davy Crockett warhead, which went from Livermore to Los Alamos.
The period of real innovation was ending by then, anyway. Warhead designs after 1960 took on the character of model changes, with every new missile getting a new warhead for marketing reasons. The chief substantive change involved packing more fissile uranium into the secondary, as it became available with continued uranium enrichment and the dismantlement of the large high-yield bombs.

[edit] Explosive testing

Nuclear weapons are in large part designed by trial and error. The trial often involves test explosion of a prototype.
In a nuclear explosion, a large number of discrete events, with various probabilities, aggregate into short-lived, chaotic energy flows inside the device casing. Complex mathematical models are required to approximate the processes, and in the 1950s there were no computers powerful enough to run them properly. Even today's computers and simulation software are not adequate.[46]
It was easy enough to design reliable weapons for the stockpile. If the prototype worked, it could be weaponized and mass produced.
It was much more difficult to understand how it worked or why it failed. Designers gathered as much data as possible during the explosion, before the device destroyed itself, and used the data to calibrate their models, often by inserting fudge factors into equations to make the simulations match experimental results. They also analyzed the weapon debris in fallout to see how much of a potential nuclear reaction had taken place.

[edit] Light pipes

An important tool for test analysis was the diagnostic light pipe. A probe inside a test device could transmit information by heating a plate of metal to incandescence, an event that could be recorded at the far end of a long, very straight pipe.
The picture below shows the Shrimp device, detonated on March 1, 1954 at Bikini, as the Castle Bravo test. Its 15-megaton explosion was the largest ever by the United States. The silhouette of a man is shown for scale. The device is supported from below, at the ends. The pipes going into the shot cab ceiling, which appear to be supports, are diagnostic light pipes. The eight pipes at the right end (1) sent information about the detonation of the primary. Two in the middle (2) marked the time when x-radiation from the primary reached the radiation channel around the secondary. The last two pipes (3) noted the time radiation reached the far end of the radiation channel, the difference between (2) and (3) being the radiation transit time for the channel.[47]
Castle Bravo Shrimp composite.png
From the shot cab, the pipes turned horizontal and traveled 7500 ft (2.3 km), along a causeway built on the Bikini reef, to a remote-controlled data collection bunker on Namu Island.
While x-rays would normally travel at the speed of light through a low density material like the plastic foam channel filler between (2) and (3), the intensity of radiation from the exploding primary created a relatively opaque radiation front in the channel filler which acted like a slow-moving logjam to retard the passage of radiant energy. While the secondary is being compressed via radiation induced ablation, neutrons from the primary catch up with the x-rays, penetrate into the secondary and start breeding tritium with the third reaction noted in the first section above. This Li-6 + n reaction is exothermic, producing 5 MeV per event. The spark plug is not yet compressed and thus is not critical, so there won't be significant fission or fusion. But if enough neutrons arrive before implosion of the secondary is complete, the crucial temperature difference will be degraded. This is the reported cause of failure for Livermore's first thermonuclear design, the Morgenstern device, tested as Castle Koon, April 7, 1954.
These timing issues are measured by light-pipe data. The mathematical simulations which they calibrate are called radiation flow hydrodynamics codes, or channel codes. They are used to predict the effect of future design modifications.
It is not clear from the public record how successful the Shrimp light pipes were. The data bunker was far enough back to remain outside the mile-wide crater, but the 15-megaton blast, two and a half times greater than expected, breached the bunker by blowing its 20-ton door off the hinges and across the inside of the bunker. (The nearest people were twenty miles (32 km) farther away, in a bunker that survived intact.)[48]

[edit] Fallout analysis

The most interesting data from Castle Bravo came from radio-chemical analysis of weapon debris in fallout. Because of a shortage of enriched lithium-6, 60% of the lithium in the Shrimp secondary was ordinary lithium-7, which doesn't breed tritium as easily as lithium-6 does. But it does breed lithium-6 as the product of an (n, 2n) reaction (one neutron in, two neutrons out), a known fact, but with unknown probability. The probability turned out to be high.
Fallout analysis revealed to designers that, with the (n, 2n) reaction, the Shrimp secondary effectively had two and half times as much lithium-6 as expected. The tritium, the fusion yield, the neutrons, and the fission yield were all increased accordingly.[49]
As noted above, Bravo's fallout analysis also told the outside world, for the first time, that thermonuclear bombs are more fission devices than fusion devices. A Japanese fishing boat, the Lucky Dragon, sailed home with enough fallout on its decks to allow scientists in Japan and elsewhere to determine, and announce, that most of the fallout had come from the fission of U-238 by fusion-produced 14 MeV neutrons.

[edit] Underground testing

Subsidence Craters at Yucca Flat, Nevada Test Site.
The global alarm over radioactive fallout, which began with the Castle Bravo event, eventually drove nuclear testing underground. The last U.S. above-ground test took place at Johnston Island on November 4, 1962. During the next three decades, until September 23, 1992, the United States conducted an average of 2.4 underground nuclear explosions per month, all but a few at the Nevada Test Site (NTS) northwest of Las Vegas.
The Yucca Flat section of the NTS is covered with subsidence craters resulting from the collapse of terrain over radioactive underground caverns created by nuclear explosions (see photo).
After the 1974 Threshold Test Ban Treaty (TTBT), which limited underground explosions to 150 kilotons or less, warheads like the half-megaton W88 had to be tested at less than full yield. Since the primary must be detonated at full yield in order to generate data about the implosion of the secondary, the reduction in yield had to come from the secondary. Replacing much of the lithium-6 deuteride fusion fuel with lithium-7 hydride limited the tritium available for fusion, and thus the overall yield, without changing the dynamics of the implosion. The functioning of the device could be evaluated using light pipes, other sensing devices, and analysis of trapped weapon debris. The full yield of the stockpiled weapon could be calculated by extrapolation.

[edit] Production facilities

When two-stage weapons became standard in the early 1950s, weapon design determined the layout of the new, widely dispersed U.S. production facilities, and vice versa.
Because primaries tend to be bulky, especially in diameter, plutonium is the fissile material of choice for pits, with beryllium reflectors. It has a smaller critical mass than uranium. The Rocky Flats plant near Boulder, Colorado, was built in 1952 for pit production and consequently became the plutonium and beryllium fabrication facility.
The Y-12 plant in Oak Ridge, Tennessee, where mass spectrometers called Calutrons had enriched uranium for the Manhattan Project, was redesigned to make secondaries. Fissile U-235 makes the best spark plugs because its critical mass is larger, especially in the cylindrical shape of early thermonuclear secondaries. Early experiments used the two fissile materials in combination, as composite Pu-Oy pits and spark plugs, but for mass production, it was easier to let the factories specialize: plutonium pits in primaries, uranium spark plugs and pushers in secondaries.
Y-12 made lithium-6 deuteride fusion fuel and U-238 parts, the other two ingredients of secondaries.
The Savannah River plant in Aiken, South Carolina, also built in 1952, operated nuclear reactors which converted U-238 into Pu-239 for pits, and converted lithium-6 (produced at Y-12) into tritium for booster gas. Since its reactors were moderated with heavy water, deuterium oxide, it also made deuterium for booster gas and for Y-12 to use in making lithium-6 deuteride.

[edit] Warhead design safety

Because even low-yield nuclear warheads have astounding destructive power, weapon designers have always recognised the need to incorporate mechanisms and associated procedures intended to prevent accidental detonation.
A diagram of the Green Grass warhead's steel ball safety device, shown left, filled (safe) and right, empty (live). The steel balls were emptied into a hopper underneath the aircraft before flight, and could be re-inserted using a funnel by rotating the bomb on its trolley and raising the hopper.
Gun-type weapons
It is inherently dangerous to have a weapon containing a quantity and shape of fissile material which can form a critical mass through a relatively simple accident. Because of this danger, the propellant in Little Boy (four bags of cordite) was inserted into the bomb in flight, shortly after takeoff on August 6, 1945. This was the first time a gun-type nuclear weapon had ever been fully assembled.
If the weapon falls into water, the moderating effect of the water can also cause a criticality accident, even without the weapon being physically damaged. Similarly, a fire caused by an aircraft crashing could easily ignite the propellant, with catastrophic results. Gun-type weapons have always been inherently unsafe.
In-flight pit insertion
Neither of these effects is likely with implosion weapons since there is normally insufficient fissile material to form a critical mass without the correct detonation of the lenses. However, the earliest implosion weapons had pits so close to criticality that accidental detonation with some nuclear yield was a concern.
On August 9, 1945, Fat Man was loaded onto its airplane fully assembled, but later, when levitated pits made a space between the pit and the tamper, it was feasible to use in-flight pit insertion. The bomber would take off with no fissile material in the bomb. Some older implosion-type weapons, such as the US Mark 4 and Mark 5, used this system.
In-flight pit insertion will not work with a hollow pit in contact with its tamper.
Steel ball safety method
As shown in the diagram above, one method used to decrease the likelihood of accidental detonation employed metal balls. The balls were emptied into the pit: this prevented detonation by increasing the density of the hollow pit, thereby preventing symmetrical implosion in the event of an accident. This design was used in the Green Grass weapon, also known as the Interim Megaton Weapon, which was used in the Violet Club and Yellow Sun Mk.1 bombs.
One-Point Safety Test.svg
Chain safety method
Alternatively, the pit can be "safed" by having its normally hollow core filled with an inert material such as a fine metal chain, possibly made of cadmium to absorb neutrons. While the chain is in the center of the pit, the pit can not be compressed into an appropriate shape to fission; when the weapon is to be armed, the chain is removed. Similarly, although a serious fire could detonate the explosives, destroying the pit and spreading plutonium to contaminate the surroundings as has happened in several weapons accidents, it could not cause a nuclear explosion.
Wire safety method
The US W47 warhead used in Polaris A1 and Polaris A2 had a safety device consisting of a boron-coated wire inserted into the hollow pit at manufacture. The warhead was armed by withdrawing the wire onto a spool driven by an electric motor. Once withdrawn the wire could not be re-inserted.[50]
One-point safety
While the firing of one detonator out of many will not cause a hollow pit to go critical, especially a low-mass hollow pit that requires boosting, the introduction of two-point implosion systems made that possibility a real concern.
In a two-point system, if one detonator fires, one entire hemisphere of the pit will implode as designed. The high-explosive charge surrounding the other hemisphere will explode progressively, from the equator toward the opposite pole. Ideally, this will pinch the equator and squeeze the second hemisphere away from the first, like toothpaste in a tube. By the time the explosion envelops it, its implosion will be separated both in time and space from the implosion of the first hemisphere. The resulting dumbbell shape, with each end reaching maximum density at a different time, may not become critical.
Unfortunately, it is not possible to tell on the drawing board how this will play out. Nor is it possible using a dummy pit of U-238 and high-speed x-ray cameras, although such tests are helpful. For final determination, a test needs to be made with real fissile material. Consequently, starting in 1957, a year after Swan, both labs began one-point safety tests.
Out of 25 one-point safety tests conducted in 1957 and 1958, seven had zero or slight nuclear yield (success), three had high yields of 300 t to 500 t (severe failure), and the rest had unacceptable yields between those extremes.
Of particular concern was Livermore's W47 warhead for the Polaris submarine missile. The last test before the 1958 moratorium was a one-point test of the W47 primary, which had an unacceptably high nuclear yield of 400 lb (180 kg) of TNT equivalent (Hardtack II Titania). With the test moratorium in force, there was no way to refine the design and make it inherently one-point safe. Los Alamos had a suitable primary that was one-point safe, but rather than share with Los Alamos the credit for designing the first SLBM warhead, Livermore chose to use mechanical safing on its own inherently unsafe primary. The wire safety scheme described above was the result.[51]
It turns out that the W47 may have been safer than anticipated. The wire-safety system may have rendered most of the warheads "duds," unable to fire when detonated.[51]
When testing resumed in 1961, and continued for three decades, there was sufficient time to make all warhead designs inherently one-point safe, without need for mechanical safing.
Strong link weak link
A strong link/weak link and exclusion zone nuclear detonation mechanism is a form of automatic safety interlock.
Permissive Action Links
In addition to the above steps to reduce the probability of a nuclear detonation arising from a single fault, locking mechanisms referred to by NATO states as Permissive Action Links are sometimes attached to the control mechanisms for nuclear warheads. Permissive Action Links act solely to prevent the unauthorised use of a nuclear weapon.

[edit] References

[edit] Bibliography

[edit] Notes

  1. ^ The physics package is the nuclear explosive module inside the bomb casing, missile warhead, or artillery shell, etc., which delivers the weapon to its target. While photographs of weapon casings are common, photographs of the physics package are quite rare, even for the oldest and crudest nuclear weapons. For a photograph of a modern physics package see W80.
  2. ^ Life Editors (1961), "To the Outside World, a Superbomb more Bluff than Bang", Life (New York) (Vol. 51, No. 19, November 10, 1961): 34–37, retrieved 2010-06-28. Article on the Soviet Tsar Bomba test. Because explosions are spherical in shape and targets are spread out on the relatively flat surface of the earth, numerous smaller weapons cause more destruction. From page 35: ". . .five five-megaton weapons would demolish a greater area than a single 50-megatonner."
  3. ^ The United States and the Soviet Union were the only nations to build large nuclear arsenals with every possible type of nuclear weapon. The U.S. had a four-year head start and was the first to produce fissile material and fission weapons, all in 1945. The only Soviet claim for a design first was the Joe 4 detonation on August 12, 1953, said to be the first deliverable hydrogen bomb. However, as Herbert York first revealed in The Advisors: Oppenheimer, Teller and the Superbomb (W.H. Freeman, 1976), it was not a true hydrogen bomb (it was a boosted fission weapon of the Sloika/Alarm Clock type, not a two-stage thermonuclear). Soviet dates for the essential elements of warhead miniaturization – boosted, hollow-pit, two-point, air lens primaries – are not available in the open literature, but the larger size of Soviet ballistic missiles is often explained as evidence of an initial Soviet difficulty in miniaturizing warheads.
  4. ^ fr 971324, Caisse Nationale de la Recherche Scientifique (National Fund for Scientific Research), "Perfectionnements aux charges explosives (Improvements to explosive charges)", published 16 January 1951, issued 12 July 1950.
  5. ^ The main source for this section is Samuel Glasstone and Philip Dolan, The Effects of Nuclear Weapons, Third Edition, 1977, U.S. Dept of Defense and U.S. Dept of Energy (see links in General References, below), with the same information in more detail in Samuel Glasstone, Sourcebook on Atomic Energy, Third Edition, 1979, U.S. Atomic Energy Commission, Krieger Publishing.
  6. ^ Glasstone and Dolan, Effects, p. 12.
  7. ^ Glasstone, Sourcebook, p. 503.
  8. ^ "neutrons carry off most of the reaction energy," Glasstone and Dolan, Effects, p. 21.
  9. ^ a b Glasstone and Dolan, Effects, p. 21.
  10. ^ Glasstone and Dolan, Effects, p. 12–13. When one pound (454 g) of U-235 undergoes complete fission, the yield is 8 kilotons. The 13-to-16-kiloton yield of the Little Boy bomb was therefore produced by the fission no more than two pounds (907 g) of U-235, out of the 141 pounds (64 kg) in the pit. The remaining 139 pounds (63 kg), 98.5% of the total, contributed nothing to the energy yield.
  11. ^ Compere, A.L., and Griffith, W.L. 1991. "The U.S. Calutron Program for Uranium Enrichment: History,. Technology, Operations, and Production. Report," ORNL-5928, as cited in John Coster-Mullen, "Atom Bombs: The Top Secret Inside Story of Little Boy and Fat Man," 2003, footnote 28, p. 18. The total wartime output of Oralloy produced at Oak Ridge by July 28, 1945 was 165 pounds (74.68 kg). Of this amount, 84% was scattered over Hiroshima (see previous footnote).
  12. ^ "Restricted Data Declassification Decisions from 1945 until Present" – "Fact that plutonium and uranium may be bonded to each other in unspecified pits or weapons."
  13. ^ "Restricted Data Declassification Decisions from 1946 until Present"
  14. ^ a b Fissionable Materials section of the Nuclear Weapons FAQ, Carey Sublette, accessed Sept 23, 2006
  15. ^ All information on nuclear weapon tests comes from Chuck Hansen, The Swords of Armageddon: U.S. Nuclear Weapons Development since 1945, October 1995, Chucklea Productions, Volume VIII, p. 154, Table A-1, "U.S. Nuclear Detonations and Tests, 1945–1962."
  16. ^ Nuclear Weapons FAQ: 4.1.6.3 Hybrid Assembly Techniques, accessed December 1, 2007. Drawing adapted from the same source.
  17. ^ Nuclear Weapons FAQ: 4.1.6.2.2.4 Cylindrical and Planar Shock Techniques, accessed December 1, 2007.
  18. ^ "Restricted Data Declassification Decisions from 1946 until Present", Section V.B.2.k "The fact of use in high explosive assembled (HEA) weapons of spherical shells of fissile materials, sealed pits; air and ring HE lenses," declassified November 1972.
  19. ^ 4.4 Elements of Thermonuclear Weapon Design. Nuclearweaponarchive.org. Retrieved on 2011-05-01.
  20. ^ Until a reliable design was worked out in the early 1950s, the hydrogen bomb (public name) was called the superbomb by insiders. After that, insiders used a more descriptive name: two-stage thermonuclear. Two examples. From Herb York, The Advisors, 1976, "This book is about ... the development of the H-bomb, or the superbomb as it was then called." p. ix, and "The rapid and successful development of the superbomb (or super as it came to be called) . . ." p. 5. From National Public Radio Talk of the Nation, November 8, 2005, Siegfried Hecker of Los Alamos, "the hydrogen bomb – that is, a two-stage thermonuclear device, as we referred to it – is indeed the principal part of the US arsenal, as it is of the Russian arsenal."
  21. ^ a b Howard Morland, "Born Secret," Cardozo Law Review, March 2005, pp. 1401–1408.
  22. ^ "Improved Security, Safety & Manufacturability of the Reliable Replacement Warhead," NNSA March 2007.
  23. ^ A 1976 drawing which depicts an interstage that absorbs and re-radiates x-rays. From Howard Morland, "The Article," Cardozo Law Review, March 2005, p 1374.
  24. ^ "ArmsControlWonk: FOGBANK", March 7, 2008. (Accessed 2010-04-06)
  25. ^ "SAND8.8 – 1151 Nuclear Weapon Data – Sigma I," Sandia Laboratories, September 1988.
  26. ^ The Greenpeace drawing. From Morland, Cardozo Law Review, March 2005, p 1378.
  27. ^ Herbert York, The Advisors: Oppenheimer, Teller and the Superbomb (1976).
  28. ^ "The ‘Alarm Clock' ... became practical only by the inclusion of Li6 (in 1950) and its combination with the radiation implosion." Hans A. Bethe, Memorandum on the History of Thermonuclear Program, May 28, 1952.
  29. ^ See map.
  30. ^ 4.5 Thermonuclear Weapon Designs and Later Subsections. Nuclearweaponarchive.org. Retrieved on 2011-05-01.
  31. ^ Operation Hardtack I. Nuclearweaponarchive.org. Retrieved on 2011-05-01.
  32. ^ Operation Redwing. Nuclearweaponarchive.org. Retrieved on 2011-05-01.
  33. ^ Weapon and Technology: 4th Generation Nuclear Nanotech Weapons. Weapons.technology.youngester.com (2010-04-19). Retrieved on 2011-05-01.
  34. ^ Fourth Generation Nuclear Weapons. Nuclearweaponarchive.org. Retrieved on 2011-05-01.
  35. ^ Never say "never". Whyfiles.org. Retrieved on 2011-05-01.
  36. ^ Samuel Glasstone, The Effects of Nuclear Weapons, 1962, Revised 1964, U.S. Dept of Defense and U.S. Dept of Energy, pp.464–5. This section was removed from later editions, but, according to Glasstone in 1978, not because it was inaccurate or because the weapons had changed.
  37. ^ "Nuclear Weapons FAQ: 1.6".
  38. ^ "Neutron bomb: Why 'clean' is deadly". BBC News. July 15, 1999. Retrieved January 6, 2010.
  39. ^ Broad, William J. (7 September 1999), "Spies versus sweat, the debate over China's nuclear advance," The New York Times, p 1. The front page drawing was similar to one that appeared four months earlier in the San Jose Mercury News.
  40. ^ Jonathan Medalia, "The Reliable Replacement Warhead Program: Background and Current Developments," CRS Report RL32929, Dec 18, 2007, p CRS-11.
  41. ^ Richard Garwin, "Why China Won't Build U.S. Warheads", Arms Control Today, April–May 1999.
  42. ^ Home – NNSA
  43. ^ DoE Fact Sheet: Reliable Replacement Warhead Program
  44. ^ William J. Broad, "The Hidden Travels of The Bomb: Atomic insiders say the weapon was invented only once, and its secrets were spread around the globe by spies, scientists and the covert acts of nuclear states," New York Times, December 9, 2008, p D1.
  45. ^ Sybil Francis, Warhead Politics: Livermore and the Competitive System of Nuclear Warhead Design, UCRL-LR-124754, June 1995, Ph.D. Dissertation, Massachusetts Institute of Technology, available from National Technical Information Service. This 233-page thesis was written by a weapons-lab outsider for public distribution. The author had access to all the classified information at Livermore that was relevant to her research on warhead design; consequently, she was required to use non-descriptive code words for certain innovations.
  46. ^ Walter Goad, Declaration for the Wen Ho Lee case, May 17, 2000. Goad began thermonuclear weapon design work at Los Alamos in 1950. In his Declaration, he mentions "basic scientific problems of computability which cannot be solved by more computing power alone. These are typified by the problem of long range predictions of weather and climate, and extend to predictions of nuclear weapons behavior. This accounts for the fact that, after the enormous investment of effort over many years, weapons codes can still not be relied on for significantly new designs."
  47. ^ Chuck Hansen, The Swords of Armageddon, Volume IV, pp. 211–212, 284.
  48. ^ Dr. John C. Clark, as told to Robert Cahn, "We Were Trapped by Radioactive Fallout," The Saturday Evening Post, July 20, 1957, pp. 17–19, 69–71.
  49. ^ Richard Rhodes, Dark Sun; the Making of the Hydrogen Bomb, Simon and Schuster, 1995, p. 541.
  50. ^ Chuck Hansen, The Swords of Armageddon, Volume VII, pp. 396–397.
  51. ^ a b Sybil Francis, Warhead Politics, pp. 141, 160.

[edit] External links