Nuclear: 07/18/11

Because some detailed nuclear-weapons information is extremely sensitive, thus classified as national-security information by nations, it is difficult to sort through the few unclassified releases of information about whether reactor-grade plutonium can be weaponized. This has been a controversial topic since at least the early 1960s. Some prominent individuals who are especially concerned about the spread of proliferation and the risks of nuclear terrorism have singled out reactor-grade plutonium as a weak link in proliferation barriers.

Other knowledgeable individuals, equally opposed to external hazards in life, have interpreted public data to indicate that making nuclear weapons out of reactor-grade plutonium has been over-hyped.

This particular Knol is devoted to describing and clarifying the controversy. While no final judgment can be made on the basis of public information, there is considerable circumstantial information to advise the difficulties of even trying to make such inferior weapons.

J. Carson Mark. Particularly unjustified has been selective “milking” of publications written by J. Carson Mark, who headed Los Alamos’ weapons-theory branch early in the Cold War. Some nonproliferation dogmatists have been exploiting his written words to support their otherwise unfounded alarmism.

Mark wrote a paper, “Reactor-Grade Plutonium’s Explosive Properties,” a definitive description of the topic published in 1990 by the Nuclear Control Institute.[1] At the behest of the Department of Energy, a revised version, “Explosive Properties of Reactor-Grade Plutonium,” was published in a 1993 issue of Science and Global Security (Vol. 4, pp. 111-129), which includes an “Appendix: Probabilities of Different Yields” by Frank von Hippel and Edwin Lyman. [2]

It is instructive to compare the 1990 and 1993 papers which are essentially the same except for a curious, but important difference: Missing from the 1993 version is Mark’s carefully defined term “weapon” as “an object suitable for a stockpile by a military organization.” No explanation for this obvious and crucial omission is supplied with the published revision. My personal interviews and conversations with Mark before 1993 confirmed the intended significance of his 1990 definition.

While reprints of the 1993 paper designate J. Carson Mark as the sole author, the Princeton University website index for Science and Global Security credits the revised paper to “Mark, J.C., von Hippel, F.N., Lyman, E.” The revised version acknowledges that “This article is adapted from an earlier paper” (a reference back to Mark’s original 1990 article).

Mark has often warned that plutonium of any grade (i.e., isotopic composition) could probably be incorporated into an explosive device by subnational groups to produce a fission yield of “some hundreds of tons.” But he also pointedly advised that a “military organization” (of an industrialized nation) would want warheads using fissile materials that result in a “reliable known yield” and “objects that could be turned out in production-line fashion.”

Thus, civil plutonium certainly could not directly meet Mark’s weaponization criterion; it should not be loosely represented as “weapons usable.” Normative domestic and international safeguards would be sufficient (as well as obligatory) to keep civil plutonium from being used as a nuclear explosive by anyone.

Those who bandy the vague term “weapons usable” are demonstrating their unfamiliarity with military specifications, which are explicit quality standards intended to assure predictable results with high confidence. National military organizations stipulate military-grade materials for reliable weapons, not materials that are simply “usable.”

Contrary to Mark’s more nuanced and pointedly qualified definition, the term “weapons usable” is an opportunistic equivocation not at all justified by Mark’s articles.

[Carson Mark’s Estimates]. Carson Mark calculated the range of fizzle yields to be expected from a Trinity-style device made with reactor–grade material (“Trinity” was the first test of an implosion-driven plutonium warhead, at Alamagordo, New Mexico, in 1945).

For [reactor-grade plutonium], setting the spontaneous neutron emission rate at 20x10⁵ per second is equivalent to choosing the mass as 10 kg, since the spontaneous emission rate of reactor-grade plutonium is ~200 n/s/g. According to the curve, there will always be a yield ratio of at least 2.7%, and the probability of degradation to a yield ratio less than 0.1 is about 83%. This is why it is often said that likely fizzle yields range from 100 tons to a kiloton or so, for a Trinity type of device. This is also why reactor-grade plutonium must be safeguarded — it’s possible get an explosion with the stuff. Fortunately, the technical hurdles are daunting.

Intrinsic Barriers to Weaponization. Here’s a case of identifying a glass as half-empty or half-full, depending on your viewpoint. In a National Academy of Sciences year 2000 report, the following statements are made:

If it is assumed that proliferators in all categories will ultimately be capable of obtaining reasonably pure plutonium metal starting from the dispositioned forms — as we believe to be the case — then the main intrinsic barriers in this category are those associated with deviation of the plutonium’s isotopic composition from “weapons grade.”

[The latter is validation of the importance of isotopic barriers to remilitarization.]

We rate the barrier posed by isotopic deviations from weapons grade as “moderate” in importance for host-nation breakout ... mainly because recovery of weapons-grade plutonium from dispositioned forms would permit production of weapons from existing designs without new nuclear-explosive tests, whereas use of plutonium of different isotopic compositions would be likely to entail design modifications and, even if not, would probably require new nuclear-explosive tests to confirm that the change in isotopic composition had not unacceptably degraded performance.

[Doesn’t that sound like a significant obstacle for remilitarization of dispositioned plutonium?]

In the case of theft for a proliferant state we rate the barrier likewise as “moderate” in importance: such a state would probably prefer to avoid if possible the burdens posed by isotopic deviations for design, fabrication, and maintenance of nuclear weapons, but it would also probably have the capabilities to cope with these burdens in ways that achieved a level of weapon performance adequate for a proliferant state’s initial purposes.

[Proliferant states have more than “avoided” dispositioned plutonium: They have all gone to great lengths to produce only the finest quality fissile materials for weapons.]

We rate importance of the isotopic barrier as “low” in the case of theft for a subnational group because, although the weapon-related capabilities of such a group would probably be lower than those of a proliferant state, the subnational group would be likely to be much less concerned about deviations from ideal performance — inasmuch as a lower-than-expected yield would still mean an explosive force more than adequate for the likely purposes of such a group — and probably less concerned about radiation exposures to those making and handling the weapons.

[The latter rating is reasonable. Still, it helps counterterrorism squads to know that terrorists could only blow up a city block, rather than the whole city.]

It is, nonetheless, important to move forward now with plutonium disposition—and, in that connection, important to determine the compliance of candidate approaches with the spent-fuel standard — both because disposition of excess plutonium is a process that will require decades under the best of circumstances (during which time it may be hoped that the stocks of warheads, separated plutonium, and highly enriched uranium will have been greatly reduced) and because, as the 1994 and 1995 [NAS] plutonium reports emphasized, the barriers provided by plutonium disposition against host-state breakout have arms-control and nonproliferation value through the signals they send (between the host states and to the rest of the world) about the intended irreversibility of nuclear arms reductions.

[Too bad this conclusion wasn’t reached a full decade or two ago; tangible, rather than paper progress could have been made by now.]

For the benefit of a scrutinizing reader, here are some more quotes from the Academy’s 2000 report under the subtitle of “Barriers to [weapons] utilization: deviation of isotopic composition”:

In summary, with respect to the isotopic barrier to utilization of the plutonium in nuclear weapons, we judge the [MOX burnup] options to be comparable [or better than comparable to typical spent fuel [discharged from a reactor]... and the can-in-canister option to be much worse than comparable.

I think my interlaced comments validate at least two observations: First, a person can look at these conclusions and come away with alternative outlooks about the value of isotopic degradation of fissile materials. Second, inasmuch as these propositions were put forth decades ago, demilitarization of fissile materials could have been initiated as soon as the Cold War ended (if it weren’t for political impediments created by those strongly opposed to using nuclear reactors to burn up the surplus fissile materials).

Additional supporting details are to be found later on in this Knol, as well as in Part 3 of this series.

Demilitarization Alternatives. Short of demilitarization, fissile materials could be stored in the form of dismantled or crushed nuclear-weapon pits. But storage has major drawbacks: The time lag before recovery and requalification depends on the form in which the materials were sequestered; for rapid weaponization the materials would be retained in their same chemical, metallurgical, and isotopic form. If the materials were physically broken up into smaller pieces, this would increase the refabrication time.

In any event, the amount of time it would take to reconstitute an arsenal of weapons with core material that has not been demilitarized would depend simply on standby infrastructure preparations made in stockpile-stewardship programs.

To delay their recovery for reuse, fissile materials could be stored underground (immobilized). But because of their inherent reactivity, fissile substances would have to be diluted in such a way as not to pose any type of criticality hazard, especially if the repository should be flooded with water. Vitrification, that is, incorporating the plutonium in a glass matrix, is one of the immobilization methods proposed, but it must be qualified for long-term storage under conditions where water might enter. Vitrification would indeed increase the time required to reconstitute an arsenal, possibly adding months to the recovery effort. Although vitrification has been proven safe and secure for small quantities of fissile materials, it would require significant R&D to qualify a repository matrix with weapons plutonium.

Another alternative for partially demilitarizing weapon-grade uranium or plutonium is to adulterate the materials with hazardous radiation and caustic chemicals. Mixing in radioactive and chemical poisons would be sufficient to deter governmentally unsanctioned activities (terrorists); however, the method would not be sufficient to preclude the government itself from mounting a program to chemically separate the radioactive or chemical adulterants.

A much longer weaponization delay could be introduced if the fissile material were incorporated into reactor fuel — and even more if the fuel was irradiated in a reactor.

The widely respected and well-informed physicist Wolfgang Panofsky took the conservative, seemingly contradictory position that [3]

All isotopes of plutonium are fissionable, and, therefore, blending weapons grade plutonium with other plutonium isotopes does not lead to material unsuitable for nuclear explosives....

Plutonium contained in the spent fuel from commercial nuclear power plants contains a mixture of isotopes different from that preferred by the nuclear weapons designers.

(For a more precise context, see the results reported in Part 2 about NAS studies, in which Panofsky participated. For a different interpretation, see statements that follow, and also the prior box about the estimates of the widely respected weapons-physicist J. Carson Mark.)

Narrowly interpreted, Panofsky’s statements are clearly true: some type of nuclear explosive could be fashioned from separated, purified reactor-grade plutonium. Evidently, his concern focused on ad-hoc weapons assembly by a have-not that could use such material to produce a highly destructive explosive or radiation-dispersal device. Dangerous as it is, such degraded material would not be suitable for replacing existing nuclear-warhead pits by the “haves.” This aspect is at the heart of the arms-control problem, a problem widely understood to be of much greater magnitude and abiding concern than proliferation or sub-national terrorism. In regard to “host-nation breakout,” which applies to existing nuclear-weapons states that have agreed to irreversibly dispose of their weapons materials, a more recent NAS study deemed that [4]

... use of plutonium of different isotopic compositions would be likely to entail design modification and, even if not, would require new nuclear-explosive tests to confirm that the change in isotopic composition had not unacceptably degraded performance.

In this connection, Panofsky recognized in 1994 that “setting a good example is a necessary part to induce the Russians to move forward rapidly.... [Some] form of subsidy from the West will be required to expedite disposition of plutonium.”

The most cost-effective means for disposition of the Russian (and other) weapons plutonium now available is through reactor degradation: this would demilitarize the plutonium so that it would not meet Mark’s criterion of being “suitable for a stockpile by a military organization.” Irradiating weapons plutonium in a reactor converts some of the fissile plutonium to non-fissile (but fissionable) even-isotopes and creates a concomitant mix of hazardous radioactive substances: this would meet the NAS “spent-fuel standard” of self-protection against diversion by subnational groups.

Most nuclear reactors can accomplish this conversion of weapons plutonium; fast-spectrum reactors could do it more rapidly.

[Can Terrorists Build Nuclear Weapons?]. Archived at the Nuclear Control Institute website is an obscure 1987 paper written by five eminent weapon-laboratory specialists who describe many inherent technical and logistical obstacles to be faced by terrorists before they could conceivably construct nuclear explosives.[5]

The authors address both crude and more sophisticated design options; the critical mass requirements of either gun- or implosion-type; the chemical and isotopic properties of fissile materials; the potential sources of such materials; and the physics concepts associated with creating nuclear explosions. They also describe the considerations necessary to take into account preinitiation, neutron reflectors, and other design factors. Formidable barriers must be overcome for terrorists to succeed in acquisition of high-grade materials from storage sites or nuclear transport.

While these Los Alamos weapons experts answer affirmatively to the rhetorical question, it is not an unambiguous or unqualified yes.

For example,

Some problems that have required a great deal of attention in the nuclear-weapons program would not seem important to terrorists. One of these would be the requirement (necessary in connection with a weapons stockpile) that devices have precisely known yields that are highly reproducible. Terrorists would not be in a position to know even the nominal yield of their device with any precision. They would not have to meet the extremely tight specifications and tolerances usual in the weapons business, although quite demanding requirements on these points would still be necessary.

Moreover,

Merely on the basis of the fact that sophisticated devices are known to be feasible, it cannot be asserted that by stealing only a small amount of fissile material a terrorist would be able to produce a device with a reliable multikiloton yield in such a small size and weight as to be easy to transport and conceal. Such an assertion ignores at least a significant fraction of the problems that weapons laboratories have had to face and resolve over the past forty years.

It is relevant to recall that today's impressively tidy weapons came about only at the end of a long series of tests that provided the basis for proceeding further. For some of these steps, full-scale nuclear tests were essential. In retrospect, not every incremental step taken would now seem necessary. Indeed, knowing only that much smaller and lighter weapons are feasible, it is possible at least to imagine going straight from the state of understanding in 1945 to a project to build a greatly improved device. The mere fact of knowing it is possible, even without knowing exactly how, would focus terrorists' attention and efforts.

To build the device would require a long course of study and a long course of hydrodynamic experimentation. To achieve the size and weight of a modern weapon while maintaining performance and confidence in performance would require one or more full-scale nuclear tests, although considerable progress in that direction could be made on the basis of nonnuclear experiments.

A terrorist group would ... have to proceed deliberately and with caution to have a good chance of avoiding any mishap in handling the material, while at the same time proceeding with all possible speed to reduce their chance of detection.

The time factor enters the picture in a quite different way. In the event of timely detection of a theft of a significant amount of fissile material — whether well suited for use in an explosive device or not — all relevant branches of a country's security forces would immediately mount an intensive response.

In sum, several conclusions concerning crude devices based on design principles can be made:

1. Such a device could be constructed by a group not previously engaged in designing or building nuclear weapons, providing a number of requirements were adequately met.

2. Successful execution would require the efforts of a team having knowledge and skills additional to those usually associated with a group engaged in hijacking a transport or conducting a raid on a plant.

3. To achieve rapid turnaround (that is, the device would be ready within a day or so after obtaining the material), careful preparations extending over a considerable period would have to have been carried out, and the materials acquired would have to be in [suitable] form.

4. The amounts of fissile material necessary would tend to be large — certainly several, and possibly ten times, the so-called formula quantities.

5. The weight of the complete device would also be large — not as large as the first atomic weapons (~10,000 pounds), since these required aero dynamic cases to enable them to be handled as bombs, but probably more than a ton.

6. The conceivable option of using oxide powder (whether of uranium or plutonium) directly, with no post-acquisition processing or fabrication, would seem to be the simplest and most rapid way to make a bomb.... We agree ... that a crude implosion device could be constructed with reactor-grade plutonium or highly enriched uranium in metal or possibly even in oxide form.

7. Devices employing metal in a crude design could certainly be constructed so as to have nominal yields in the 10 kiloton range — witness the devices used in 1945.... If a chain reaction were initiated by neutrons from some source during this [preinitiation] period, the yield realized would be smaller — possibly a great deal smaller — than the nominal yield.... The neutron source in enriched uranium is several thousand times smaller than in the plutonium referred to, so that uranium can be used in a gun-type assembly and have a tolerable preinitiation probability. [It] is necessary to have rather pure uranium metal, since even small amounts of some chemical impurities can add appreciably to the neutron source.... However, reactor-grade plutonium can be used for making nuclear weapons. [The] lowest preinitiation yield may still be in the 100-ton range, even in a crude design.

8. There are a number of obvious potential hazards in any such [terrorist] operation, among them those arising in the handling of a high explosive; the possibility of inadvertently inducing a critical configuration of the fissile material at some stage in the procedure; and the chemical toxicity or radiological hazards inherent in the materials used.

9. There are a number of other matters that will require thoughtful planning, as well as care and skill in execution. Among these are the need to initiate the chain reaction at a suitable time and for some reliable means to detonate the high explosive when and as intended.

10. Some problems that have required a great deal of attention in the nuclear-weapons program would not seem important to terrorists [such as] the requirement (necessary in connection with a weapons stockpile) that devices have [ highly reproducible] precisely known yields....

11. Throughout the discussion, it has been supposed that the terrorists were home grown. It is conceivable that such an operation could be sponsored by another country, in which case some of the motivation, technical experts, and muscle men might be brought in from outside. This difference would not change the problems that would have to be addressed or the operations required, but it could increase the assurance that important points are not overlooked. It might also provide the basis for considering a sophisticated design rather than a crude type.

The production of sophisticated devices ... should not be considered ... a possible activity for a fly-by-night terrorist group. In summary, the main concern with respect to terrorists should be focused on those in a position to build, and bring with them, their own devices, as well as on those able to steal an operable weapon.

Nothing in the cited article is inconsistent with the information presented in this Knol. However, individuals who do not have the appropriate technical experience could misconstrue the analysis.

Weaponizability of Fissile Materials

Here are some of the crucial requirements and means that affect the weaponizability of fissile materials.

Military-quality nuclear weapons require a very high (90%) concentration of fissile isotopes, primarily uranium-235 (U-235) or plutonium-239 (Pu-239). The manufacture of these fissile materials in pure enough form for nuclear weapons requires special and complicated processes to accumulate with the required isotopic and chemical purity. These conditions define a national weapons program, whether declared or clandestine.

Compared to Pu-239, the isotope U-235 is the relatively less expensive and less potent of the two principal weapon-source materials.

Many processes have been developed for uranium enrichment during and since the Cold War. In this paper, the focus is on plutonium.

Nuclear-Explosive Requirements. Acquiring weapon-grade fissile material is the most substantial barrier for a expectant weapons state. Plutonium and uranium that have fissile fractions less than 20% are considered unsuitable for any type of nuclear explosive. Thus, a wannabe weapons state has either undertake a concealed program (as Israel did) or find a way to clandestinely produce and divert weapon-grade materials.

For the purposes of military-quality weapons, the fissile plutonium isotope concentration must be at or above about 94%. Anything less would result in an explosion of uncertain yield and reliability. On the other hand, a nuclear-explosive made of uranium below weapon-grade would be more predictable, but cumbersome.

Dedicated military-production reactors are designed and operated to optimize high-quality plutonium; they do this by minimizing (even-numbered) isotopes of plutonium (Pu-240 and Pu-242) that are detrimental to military-quality nuclear explosives. Weapon-grade plutonium has a fissile fraction (Pu-239 and Pu-241) of at least 94%, whereas the plutonium byproduct from a light-water power reactor, for instance, is below 70%.

Nuclear explosive yields can be augmented by boosting which requires the special “heavy” hydrogen isotope of tritium. Thermonuclear weapons may need deuterium (another heavy isotope of hydrogen), and/or lithium-6 (an isotope separated from natural lithium). Boosting, though, does not circumvent the yield variability and unpredictably for plutonigum which does not meet military-quality standards.

Manufacturing Weapon-Grade Plutonium. Weapon-grade plutonium is manufactured in a special military-production reactor designed to yield an excess of neutrons to convert fissionable uranium-238 to fissile Pu-239 through a neutron-capture process. While other reactors — civilian power, research, or materials testing — also produce some Pu-239, the product of an unspecialized reactor is ordinarily not optimal, either in quantity or quality.

Special production reactors, which mostly contain a graphite moderator, such as the “piles”at Hanford, the RBMK ( Soviet Union), and the Magnox (Great Britain) were the mainstays for Cold War weapons plutonium.

Contemporary power reactors fueled online with natural or slightly enriched uranium, like those derived from Soviet RBMK and the Canadian CANDU, can yield weapon-grade plutonium if not make accountable through external oversight. (Such reactors are readily subject to special IAEA safeguards.) Light-water reactors, most common at nuclear-power stations throughout the world are nearly incapable of being a source of plutonium for weapons.

Fast-spectrum breeder reactors can generate byproduct plutonium that averages about 80% fissile, also well below the utility level for military weapons. Laser-isotope improvement of such plutonium might eventually be practical, but now it is still in the “iffy” stage.

Some reactor cores could be surrounded with a “blanket” of natural uranium in order to produce weapon-grade plutonium; they would then require an uncharacteristic schedule of operation, including more frequent and telltale shutdowns to avoid ruining the weapons value of the plutonium. Other types of reactors could theoretically be scheduled to shut down more frequently for core fuel element removal in order to extract high-quality plutonium. All of these stratagems result in highly observable changes in operating parameters.

In order to preclude such reactors from being used for military-production purposes, special operational process controls and international materials safeguards are preconditioned. Operational and facility transparency is the norm for NPT adherents and IAEA safeguards agreements.

Without operational transparency and fuel-management safeguards, some research and test reactors could produce significant quantities of weapon-grade plutonium. For example, relatively high-power research reactors in Israel and North Korea (which are not subject to international inspection) have such capability. If they adopted international safeguards, at best only minuscule amounts of high-grade plutonium could be diverted. (North Korea had to formally abrogate its international NPT/IAEA commitments in order to extract weapon-grade plutonium out of fuel assemblies removed from its Yongbyon reactor.)

Power-reactor fuel normally starts with 3% to 6% fissile content of uranium or plutonium, with some specialized reactors having higher fissile fraction but small inventory. Fast reactors typically has a large inventory of fuel in the range of 20% fissile. In spent-fuel discharges of thermal and fast reactors, some fuel elements could have plutonium with higher fissile fractions.

Since these routes for nuclear-materials diversion are well known, they form the basis of the very effective international-safeguards regime.

Means of Isotopic Demilitarization. An effective means of demilitarizing U-235 is the relatively straightforward process of blending (diluting) U-235 with natural or depleted uranium. This demilitarization process is being routinely carried out in accordance with a U.S. program to purchase weapon-grade uranium from Russia.

For plutonium, however, deliberate isotopic demilitarization is more difficult, but still possible. Rather than being naturally available, the demilitarizing even-isotopes of plutonium (240 and 242) are byproducts of long-term reactor operation.

With moratoria in effect on the testing and manufacture of new nuclear weapons, the long-term stability of the nuclear and non-nuclear components in a warhead becomes an important concern. In this respect, a news report says “Russian scientists have discovered that weapon-grade plutonium is far more unstable in form than previously suspected, a finding that could have implications for the aging and reliability of America’s arsenal of 10,000 or so nuclear warheads.”[6] This finding should not be unexpected, because plutonium has six allotropes (metallurgical phases), all with differing densities and volumes.[7] Each phase is stable only within a specific temperature range, or with the use of additives like gallium. If plutonium metal is overheated, it will progressively change allotropic phases. This results in expansive pressure that eventually could cause cracks in the pit or serious damage to the casing. These effects might affect the warhead’s performance and reliability. The actual range of instability for American weapons would be classified security information; and Russian weapons instabilities might differ because of dissimilar metallurgical additives and treatment.

In addition, there are “complications” introduced by the spontaneous neutrons and heat generated by the even-isotopes of plutonium. These I detailed back in the late 1970s[8], and much of the analysis has since been reinforced.

Reactor-Grade Plutonium. The debate over the reprocessing of spent (discharged) reactor fuel (in order to separate and recover fissile residues) has hinged on misunderstandings regarding the susceptibility of highly irradiated spent fuel for diversion and direct use in nuclear weapons. The vast bulk of excess reactor-grade plutonium is from stored fuel discharged from commercial nuclear power stations.

By reprocessing, the short-lived fission products can be separated from long-lived fissionable elements, which are reusable in reactors. The separated fission products, the bulk of which have relatively short lives, can be credibly stored at reduced volume for about 200 years; this concentration by reprocessing vastly diminishes the problems of radioactive byproduct storage. The separated heavy elements make excellent fissile and fertile components for reactor fuels, but they make lousy weapons (if someone, somehow, were to gain illicit access to these dangerously radioactive materials).

Huge amounts of reactor-grade plutonium are produced from the conversion of U-238 in power reactors (at the approximate average rate of 160 kg/yr-GWe). By the end of the first millennium, as much as 1600 tonnes of plutonium would have been discharged in spent fuel. This byproduct plutonium is highly radioactive and subject to careful domestic and international safeguards. Although many nations would have the technical capability to secretly develop a nuclear explosive out of reactor-grade material, the technical and procedural disincentives are strong enough to keep this pathway from being a likely avenue for weapons proliferation. Nevertheless, perpetual vigilance will be required.

Nothing written here implies that highly destructive nuclear-explosive or radioactivity-dispersion can’t be wrought from fissile materials of lower-than-military grade. However, it is abundantly clear that nations would only choose the purified high-grade fissile materials described above for war-fighting purposes. Reactor-grade plutonium, for example, has so many problems to overcome in weaponization that, so far as known, all nations have avoided that pathway.

National Academy Studies

This treatment of studies presented by the National Academy of Sciences differs from that found in Part 2, in that criticisms are examined in more detail.

The Spent-Fuel Standard and Demilitarization. If no further processing occurs to the MOX after irradiation (a once-through fuel cycle), the depleted fuel would be stored for posterity. This type of single-cycle irradiation would be sufficient to satisfy the “spent-fuel standard” suggested by the National Academy of Sciences in a 1994 report.[9] The weapons plutonium can then be considered “demilitarized.”

The MOX process therefore results in all three demilitarization treatments of weapons plutonium: isotopic dilution, radiation adulteration, and chemical adulteration. This combination introduces formidable barriers to re-use of the weapons-plutonium proliferation — a strong contribution to arms control.

In 1994 NAS issued a comprehensive report on proposed methods for disposing of fissile materials that might become surplus as a result nuclear arms reductions.[10] As an interim measure, NAS agreed that the weapons plutonium should be made as least as inaccessible as reactor grade, resulting in their so-called “spent-fuel standard.” Interim storage was recognized as necessary because long-term disposition would take decades to complete. Nevertheless, the report urged “further steps ... to move beyond the spent fuel standard and reduce the security risks posed by all of the world’s plutonium stocks....”

Through the 1990s, the quasi-technical debate about the desirability and feasibility of demilitarizing plutonium centered around two underlying issues: a policy-relevant uncertainty regarding the future of nuclear power, and a technological question regarding practical feasibility of demilitarization. Much of the debate has been emotionally charged, and some academic scientists have placed their reputations on the line.

Many who favored long-term storage of plutonium (instead of demilitarization) were seduced by two concerns: They wanted to avoid extending the lifetime of nuclear reactors, and they were not convinced of the effectiveness of demilitarization by reactor irradiation. Their persistent anti-nuclear-power tone is why we have chosen to categorize them as ideologues on this issue (lacking a better term); this tone, we find, pervades their pronouncements.

In its 1994 report on demilitarization of weapons plutonium, the NAS committee recommended three objectives: minimize (diversion) risk, minimize reversal of the arms-reduction process, and strengthen control mechanisms against proliferation. The report suggested that achievable “plutonium-consumption fractions ... are not sufficient to greatly alter the security risks posed by the material remaining in spent fuel.” So the NAS thereupon recommended “research on fission options for near-term elimination of plutonium....”

The NAS committee also recommended that interim disposition of weapons plutonium could be accomplished by methods that met their definition of the “spent-fuel standard,” that is, making the material as inaccessible as existing reactor-grade plutonium. They agreed that reactor-grade plutonium in spent-fuel rods has an inherent degree of self-protection against diversion. But they felt that interim storage was necessary because long-term disposition could take decades to complete.

Although the NAS established three standards, one each for “stored weapons,” “spent fuel” and “beyond spent fuel,” they did not come up with a definitive “weapons-substitution” standard; that is, they did not decide what degree of degradation would make plutonium no longer suitable for substitution in military-quality weapons.

Gradually the NAS moved toward acceptance of at least one reactor-irradiation phase of weapons plutonium to satisfy its spent-fuel self-protection criterion, a conclusion that started to emerge in 1995 and consummated in 2000.[11]

Despite progress in the Academy’s views of demilitarization, an obdurate and sometimes subtle opposition to reactor degradation (burnup) and isotopic conversion has been expressed by the few recalcitrant academic scientists who emphasize ideological nonproliferation objectives ahead of arms control. William Arkin, an independent commentator, has stated that “Proliferation is methadone for Cold Warriors” who are still fighting superannuated campaigns against plutonium incineration.

Committed to disapproval of nuclear power, some academics and environmentalists (see box next page about dissenters) have been unwilling to advocate or support any reactor utilization — such as the MOX cycle — that would appear to extend the lifetime of nuclear reactors. The dissenters have been unduly impressed by the long-standing insistence of a few weaponeers that plutonium cannot be “denatured.” As for the ideological motivations for opposing nuclear power, we will skirt the matter except where necessary in discussing the arms-control and nonproliferation role of reactors.

Immobilization/Vitrification Limitations. Rather than accept reactor burnup to demilitarize weapons plutonium, those favoring a more passive course proposed “immobilization,” whose final stage was underground storage. “Single-track” (immobilization) advocates would have mixed the weapons plutonium with the radioactive byproducts from reactors and “immobilized” it by vitrifying the mixture and burying the highly radioactive glass “logs” underground. Ironically, those who fear weapons plutonium and advise immobilization have come into conflict with other environmental interests that dispute government siting choices for nuclear-byproduct storage and underground burial.

Because many problems were found with the immobilization-only option, the NAS originally endorsed DOE’s “dual-track” approach of both vitrification and reactor degradation for weapons plutonium. This meant that degradation of weapons plutonium would be limited to only the first of what otherwise could be two or three cycles of irradiation and reprocessing. The study’s chairperson (John Holdren) reminded reprocessing opponents that under the “dual-track” recommendation, “There would be no reprocessing of spent fuel,” which was meant to appease the diehards, while still allowing some degradation of weapons plutonium in the first reactor irradiation phase.

To meet primary security goals, the NAS in its mid-90s studies stressed three objectives: minimize risk of diversion, minimize opportunities to reverse the arms reduction process, and strengthen control mechanisms against proliferation. Regrettably, adoption of the committee’s initial recommendation for interim — but indefinite — storage of pits and unadulterated plutonium had the effect of postponing irreversible arms reductions. Although securely stored, surplus plutonium through the years remained in forms that could be readily recovered for weapons. Pressure thus built up to move ahead with either reactor irradiation or immobilization. However, single-track immobilization — simply mixing weapon-grade plutonium with some form of radiologically contaminated byproduct — has two afflictions from which it never be free: the need for perpetual safeguards and the risk of nuclear criticality. There is also a NIMBY, not-in-my-backyard, problem too; it has been difficult to overcome a nearby locality’s opposition to underground storage of nuclear materials and byproducts — whether vitrified or ceramicized, whether enriched or depleted.

Three Strikes Against Immobilization. The process of immobilization by vitrification has three strikes against it:

(1) The radioactive byproductss admixed with weapons plutonium typically contain little of the plutonium isotopic diluents found in spent reactor fuel, so that the immobilized plutonium would remain in a form directly recoverable for reconstitution in weapons pits. Simply incorporating weapon-grade plutonium in a glass matrix does not diminish its isotopic potency, that is, its direct usefulness as a weapon material.

(2) In order to make the process affordable, a high fraction of weapons plutonium needs to be mixed with the radioactive byproducts, thus increasing the risk of spontaneous nuclear criticality during preparation and long after underground burial; underground storage, except for highly diluted fractions mixtures, might not be licensable because of these concerns about criticality.

(3) The technology for long-term stabilization of weapons plutonium in a glass matrix has not been adequately proven.

Proponents of Immobilization. Marvin Miller from MIT and Frank von Hippel from Princeton have frequently expressed their opinion that all plutonium should be immobilized (vitrified) and buried — which would not reduce its military potential. They published these thoughts again in 1997 (“Let’s reprocess the MOX plan,” The Bulletin of the Atomic Scientists (July/Aug. 1997)), even though the NAS had by then forsaken the immobilization single-track in favor of isotopic transformation of plutonium to less easily used forms.

The 1995 NAS “clarification” of its 1994 report concluded that there were “nonproliferation liabilities” in not moving ahead with “imposing some built-in [isotopic] barriers to the reuse of military plutonium.” (In fact, it was the intrinsic isotopic barriers that kept Cold War nuclear arsenals from being made of low-grade materials.)

In March/April 1997 issue of The Bulletin of the Atomic Scientists, the chairperson of the Academy study, John Holdren, publicly reversed his long-standing position, having come to realize that vitrification has the “disadvantage of not changing the weapon plutonium isotopically” (which is just what irradiation in a reactor does — it reduces the fissile composition, making the plutonium far less suitable for weapons). Holdren explained his revised views about the demilitarized nature of reactor-grade plutonium:

[Because] the isotopics are different, weapons using this plutonium would have to be redesigned, which would require nuclear tests. That means the path to reuse of spent fuel would be more difficult technically and politically — as well as easier to detect — than reusing weapons plutonium extracted from glass.

Holdren, a university physics professor, who wrote of this change of view on behalf of NAS study, candidly acknowledged:

those who know my history know that I did not reach these positions because of lack of concern about proliferation or any history of understatement of the proliferation dangers of plutonium recycle.

While the same worthy concern is shared by Miller and von Hippel, they are handicapped by their persistence in labeling plutonium “weapons usable” — an imprecise and ambiguous term obscuring the crucial fact that isotopic quality significantly affects a weapon’s yield, reliability, complexity, stability, and ease of manufacture. They have remarked that they relied on the “U.S. weapons experts” for guidance. If, instead, they placed greater emphasis on fundamental nuclear physics, they might have come to the conclusions ultimately reached by their scientific and engineering peers at the Academy.

Von Hippel, in July 1998, well after Academy’s 1995 recantation, wrote in Nature that “Plutonium separated from fuel in nuclear power reactors can easily be stolen and is directly usable in weapons.” If one considers that the nuclear age began more than a half-century ago, and weaponization of reactor plutonium has yet to happen, it cannot be as easy or usable as he insists.

Opposition to reactor degradation, stemming from misdirected fear of nuclear power, is often disguised as environmentalism. For example, Arjun Makhijani, a self-styled environmentalist, in the February 2001 issue of his in-house publication Science for Democratic Action, argues that converting weapons plutonium in commercial plants raises concerns about proliferation and safety (due to the use of plutonium as fuel). He also mentions transportation and security issues. He prefers single-track immobilization, which he considers to be safer, faster, and cheaper — ignoring the 1999 NAS report that pointed out that immobilization was going nowhere.

Without forsaking his nonproliferation credentials, Holdren has since reaffirmed the Academy consensus and his own revised reasoning that disposing of fissile materials to effectively preclude re-use in weapons represents one of the most urgent and cost-effective tasks of arms control and nonproliferation. In his view, U.S. participation in weapons-plutonium degradation would pose a smaller and more manageable danger than leaving the stockpiles untreated.

Professors Miller and Von Hippel, having seen the National Academy of Sciences adopt a “dual-track” course, did not publicly abandon advocacy of the single-track burial approach. They continued to advocate that plutonium should be “immobilized” underground without reducing its military potential. The Academy late recanted their original single-track burial recommendation, having found that the immobilization concept did not benefit arms control and nonproliferation as well as the built-in isotopic barriers of MOX irradiation.

Also of fundamental importance is that the NAS in its 2000 report recognized that various interim storage configurations (such as “can-in-canister”) were vulnerable to “on-site attack” while the plutonium was still in a form lacking isotopic barriers to reuse in nuclear weapons.

A Compromising Alternative. A two-fold approach, immobilizing reactor-grade plutonium (civilian fuel) and demilitarizing weapon-grade plutonium, would be good choice because reactor-grade material is produced in commercial plants, and weapon-grade plutonium is from surplus military weapons and stockpiles. A modified dual-track approach — vitrification of spent civil fuel and MOX burnup of weapons plutonium — would have been a wise compromise and better use of scarce resources. By reprocessing leftovers from the first reactor incineration phase, and by continuing the cycle of burnup and reprocessing, the weapons plutonium could be converted isotopically to material practically useless for military applications. Simplified, the two modified parallel pathways would then be:

RG Pu: vitrify spent fuel and store underground

WG Pu: convert to MOX ; get isotopic depletion by reactor burnup; then vitrify spent fuel and store underground

Spent reactor fuel is not now normally processed into its constituents. As a result, the untreated fuel is stored at increasingly congested reactor sites, awaiting transport to — and interim storage at — a national site (in Nevada). Because repository fuel storage consumes considerable underground space and its internal integrity to radioactive fission products is deteriorating, it would be better to process the fuel and then store or recycle the byproducts. In today’s factional environment, it has not been possible to do this.

Garwin’s Baffling Views. In an unpublished paper by Richard L. Garwin, a Manhattan-Project physicist and frequently sought advisor to national committees, his bottom-line view is that separated reactor plutonium should be safeguarded just as thoroughly as weapon-grade materials; indeed, I agree that reactor-grade plutonium can be made into a devastating nuclear explosive (but, experientially, not a qualified nuclear weapon).

The self-evident disutility of substituting reactor-grade plutonium within existing nuclear weapons is widely underrated, especially in the United States. This is of considerable importance in facilitating the nuclear-weapon “prohibition” goal mentioned by Garwin in the context of the NAS CISAC report.

Garwin, in my opinion, understates the engineering difficulties of efficient heat dissipation from a pit. He does not address the U.S. government’s withholding of additional information about a 1962 nuclear explosion allegedly using reactor-grade plutonium. The publication of this information would go a long way toward clarification.

In any event, a realistic boundary condition is set by the fact that of nearly a dozen or so nations which have developed or seriously endeavored to develop nuclear weapons, none are known to have truly sought or adopted reactor-grade plutonium for their pits.

There is also a NIMBY (“not in my backyard”) problem: The State of Nevada seems implacably opposed to underground storage of nuclear materials and byproducts — whether vitrified or ceramicized, whether enriched or depleted.

These circumstances weigh heavily in favor of a U.S. program operated through and at government facilities to process and burn spent fuel in civilian reactors (see Part 5).

Expert Disagreement on Weapons Usability. A. David Rossin, a former DOE official who had substantial nuclear-technology experience before entering government service, writes that long ago he first heard from Tom Cochran of the NRDC the term “weapons-usable.” Rossin agrees that — despite the large body of contradictory evidence — the term is often applied by “today’s nonproliferation activists” indiscriminately to “all isotopes of plutonium.”[12] Rossin notes that “a credible nuclear deterrent” must have “reliable deliverable WEAPONS that can be safely stored and ready to use” — characteristics not at all attributable to anything less than weapon-grade plutonium.

A former official of the IAEA, Bruno Pellaud, published in 2002 his overview of the proliferation potential of plutonium.[13] After a detailed examination of the technical literature, and carefully clarifying the explosive capability of various plutonium isotopic mixtures, Pellaud proposed that — in order to assign safeguards verification to useful security — plutonium be categorized in three functional grades and five realistic forms depending on origin. This would lead, in his opinion, to a “political balancing act between the perceptions and reality of risks.”

Using his technical and managerial experience as director of IAEA Safeguards, Pellaud assessed practical plutonium materials security, one of the obstacles being dogmatic usage of an unjustified terminology:[14]

...many [American scholars and officials] have repeatedly argued against reprocessing and plutonium recycle elsewhere in the world, still under the impression of the alleged reactor-grade nuclear test of 1962, and dogmatically bound to the questionable claim that all plutonium is weapons usable. In international forums, they have thus refused to contemplate a categorization of Pu and any other reassessment of the relevant verification criteria.

Behind a veil of secrecy, the opinion of weapon designers is short-handedly invoked to validate preset positions. While recognizing the need for confidentiality, the independent observer too often gains the impression of a lack of technical objectivity [by the dogmatists who intone that all plutonium is “weapons-usable”].

Interim and Alternative Treatments. Another way to introduce radioactive and isotopic impediments to weapons re-use is to directly mix weapon-grade plutonium with discharged reactor fuel.[15] The Department of Energy has sufficient stocks of spent fuel to carry out a test program, and it has already partially developed a pyroprocessing technology that could blend weapons plutonium with spent fuel. There is a huge inventory of used commercial fuel destined for interim storage in Nevada. While this plan would not reduce the isotopic content of weapons plutonium as much as irradiation in a reactor, it would provide some isotopic degradation and add considerable resistance to diversion or reuse. The concept, however, is politically hampered by being akin to “reprocessing” and being a means that could be used in a closed-cycle fast-reactor program (with or without “breeding”).

A compromise strategy might consist of immobilizing spent reactor fuel, but irradiating and burning weapons plutonium in reactors.

International and domestic safeguarding of all plutonium (and uranium) is essential; it is also sufficient to impede acquisition for non-sanctioned diversion. Demilitarization of plutonium would significantly impede the rebuilding of arsenals that were reduced after the Cold War.

Moreover, if weapons plutonium were to be isotopically depleted beyond the spent-fuel standard (by longer incineration in a reactor), even greater inherent obstacles would be raised against rapid reconstitution of nuclear arsenals.

In the meantime, more than a decade of opportunity for demilitarization since the end of the Cold War has been squandered, much of the lost time resulting from misplaced opposition to the needed processes.

If it were true, as a few academics allege, that “reactor-grade plutonium can be used to make weapons at all levels of technical sophistication,” then the public, Congress, and policy makers have been subjected to a half-century scam perpetrated by weapons designers who spent great sums of public money generating unneeded weapon-grade plutonium. If reactor-grade was so good, why not simply use the much-less-expensive material for weapons?

When applied to all forms of plutonium, indiscriminate usage of the term “weapons usable,” has been an issue-clouding travesty impeding realistic steps in the direction of nuclear disarmament. Also distorting the debate has been excessive emphasis on the uncontested fact that it is theoretically possible to build a nuclear explosive from separated reactor-grade plutonium; it would indeed be a highly destructive device, but not good enough for inclusion in a national arsenal.

Professors Miller and Von Hippel, who used the term “obdurateness” to characterize the reasoning of others, have underrated the advantages of moving expeditiously toward irreversible isotopic demilitarization of weapons-plutonium stockpiles.[16] Fortunately, their advocacy of storing weapons plutonium in a vitrified form (which would be relatively easy to reprocess into weapons) seems to be derived not from nonproliferation goals, but more from their oft-expressed antipathy to nuclear power, especially fast reactors.

The path to proliferation is clearly conditioned by physical, engineering, political, economic, and concealment imperatives that have led real-world first-time bomb-makers to favor uranium, not plutonium — and especially not reactor-grade plutonium. Misunderstandings about weaponizability have had some impact on post-Cold-War proliferation policy, but they have a greater bearing on future pathways available for demilitarization. While a few academics, for whatever reasons, decry the widespread use of civilian nuclear power, this bias should not be allowed to interfere with the task of ensuring that nuclear arms are demilitarized as rapidly and assuredly as possible. The key is to make plutonium (and uranium) stocks as resistant to weaponizability as feasible.

Crusaders against nuclear reactors and reprocessing have been more concerned about hypothetical dangers than the more realistic perils from materials now being surplused from nearly 50,000 remaining nuclear warheads, thereby creating stockpiles of rapidly accessible weapon-grade nuclear material.

[Some Selected Highlights of the NAS 2000 Report]. [My comments are italicized in brackets.]

Barriers provided by plutonium disposition against host-state breakout have arms-control and nonproliferation value through the signals they send (between the host states and to the rest of the world) about the intended irreversibility of nuclear arms reductions.

[Although oblique and belated, this is a crucial admission of the unsuitability and irreversibility of reactor-incinerated plutonium.]

We rate importance of the isotopic barrier as “low” in the case of theft for a subnational group.

[Isotopic barriers (e.g., reactor-grade compared to weapons-grade plutonium) are not needed for this scenario because spent fuel is normally well safeguarded and trackable if it were stolen.]

The use of plutonium of different isotopic compositions would be likely to entail design modifications and, even if not, would probably require new nuclear-explosive tests to confirm that the change in isotopic composition had not unacceptably degraded performance.

[This is the NAS’s most important revelation about the durability of isotopic depletion; it confirms the difficulties that would have to be overcome by existing weapons states which have carefully chosen standby maintenance procedures, specialized delivery systems, and singular military missions for nuclear weapons in their arsenal.]

The reference can-in-canister option is much worse on isotopic composition; worse on quantity of material to be processed; better on item mass/bulk and technical difficulty of disassembly; and comparable on five other barriers.

[Essentially a death blow to can-in-canister and most other storage “dispositioning” schemes that don’t alter isotopic composition of the plutonium.]

In summary, with respect to the isotopic barrier to utilization of the plutonium in nuclear weapons, we judge the LWR-MOX and standard CANDU-MOX options to be comparable to typical spent fuel, the CANFLEX-CANDU option to be better than comparable, and the can-in-canister option to be much worse than comparable.

[This reflects an NAS evolution towards practicality.]

Independent Studies

In recent years, a team of scientists retired from institutes in Germany and Switzerland has jointly carried out intense analyses and modeling of explosive-yield limitations and fabrication difficulties for devices hypothetically filled with degraded forms of plutonium.[17] Their independent results and interpretation of feasibility are at odds with those of J.C. Mark and the U.S. National Academy of Sciences panel reports.

In addition, the retired scientists developed, in diagrammatic detail, a conceptual plan for a phased strategy in establishing and maintaining an international proliferation-resistant civilian nuclear fuel cycle. These results are just now (2008) in different stages of publication.

To distinguish their computations from my remarks earlier in this three-part Knol, keep in mind that, on the basis of several considerations, I have challenged the NAS loose interpretation of a “weapon,” which is more carefully and significantly defined by Mark as“an object suitable for a stockpile by a military organization.” As explained, a broader interpretation is not consistent with his stated intentions or his published articles, nor does it reflect common usage or historical experience.

In my own publications published in late 1970s and early 1980s, I differentiated between different assumed technological capabilities that would characterize three levels of technical sophistication and resources: (1) national military organizations, (2) aspiring nuclear-weapons states with limited capabilities, and (3) non-state groups. The most likely capabilities of non-state groups is to fashion a nuclear explosive, as differentiated from a nuclear weapon. This segregation is necessary in order to manage a practical non-proliferation policy. Only in their latest reports has the NAS moved toward, but not gotten to, a sufficient parametric matrix analysis.

Independently, this group of retired European scientists has carried out detailed calculations that come up with reactor-grade plutonium peak explosive yields of 0.12 kt to 0.35 kt, parameterized according to technology assumptions, in comparison to Mark’s value of 0.54 kt for his single set of conditions. The parameterized calculations are closer to my published values than they are to Mark’s. More important for military strategists, however, are average yields and statistical spread. In neither category does reactor-grade plutonium compete without extensive redesign and testing of remodeled explosive devices.

Notably, these peak explosive results challenge the 1994 NAS declaration that “with relatively simple designs ...nuclear explosives could be constructed [out of reactor-grade plutonium] that would be assured of having yields of at least 1 or 2 kilotons.”

A significant thrust for the retired scientists has been on evaluating compositions that include Pu-238 and Am-241 in order to increase random-neutron-induced pre-ignition and heat-induced stress. (My earlier calculations were primarily a parametric analysis of the evolving effect of plutonium even-isotope buildup during reactor burnup.) The calculations by Kessler, et al, show that inherent alpha-particle induced heat (almost a kilowatt) creates very difficult design and deployment conditions if the devices were comprised of reactor-grade plutonium.

Moreover, this team took Mark’s 1993 modeling conditions as a point of departure. If based on anything other than Mark’s careful differentiation, inferences drawn regarding technical and pragmatic weaponizability of reactor-grade plutonium are subject to stronger framework challenge, as explained elsewhere within this Knol series,.

Of considerable counter-proliferation value is the strategy proposed by the European scientists for a two-phase proliferation-resistant civilian fuel cycle. This strategy is described with conceptual diagrams and numerical results for thermal and fast reactors. Specifically, they arrive at a weapons-plutonium destruction rate (consumption rate) of 430 kg/Pu/GWe-y.

There exist a few other published analyses of reactor-grade plutonium, but none go into detail that this group of experienced nuclear physicists has carried out.

Saga of the Soviet Dual-Purpose Reactors

One of the sorriest examples of mischaracterized nuclear threats I can think of has been U.S. policy regarding three Soviet dual-purpose (military and civilian) reactors in Russia (although it had far less in impact than the Chernobyl overreaction — see my Knol, ETHICS IN SCIENCE: The Exaggeration of Radiation Hazards).

During the Clinton administration, agreements were reached for shutting down the three Russian plutonium-production reactors, but no deadline could be negotiated because of lack of practical replacement of their secondary output, namely community heating and electricity. Without these reactor byproducts, the surrounding cities would not be able to endure the Siberian winters nor convert from military to civilian enterprises.

U.S. insistence on shutdown without replacement, or other interim measures such as highly polluting coal-fired plants lacking economical access to coal supplies, were based on a combination of overreactions about about Chernobyl-like accidents and about prolonging weapon-grade plutonium production.

The reactor-safety concern was being met by upgrading reactor operation and safety of all former production-style reactors. However, Clinton administration advisors were also or more worried about the continued byproduct of weapon-grade plutonium. Had they recognized that by extending the burnup of the fuel (including hardier fuel-container design longer irradiation), the degraded highly irradiated plutonium would not have been serviceable for existing nuclear weapons, they might then have realized that immediate or uncompensated shutdown was impractical.

It took until 2008 before two of the three reactors shut down. The United States had to contribute almost $1billion for refurbishing nearby fossil fuel and wind plants to compensate for the loss of energy.

More details can be found in Part 4 of this series and in Nuclear Shadowboxing, Volume II.

Economic and Infrastructure Issues

In the Academy’s 2000 report, it is noted that “use of plutonium under current conditions can only be done at an economic loss.” While true at the time, it is hardly a fatal limitation. For one thing, the conclusion is heavily dependent on what infrastructure or program the task is piggy-backed.

The economic value of the combined existing world arsenal, say 300 tonnes of excessed military plutonium, would recover billions of dollars at current prices (see the fifth Knol in this series) as commercial nuclear-reactor fuel — a significant offset to the costs of achieving international demilitarization.

Each of the weapons-states operates reactors that could be fueled with MOX. Reactor fuel bundles are routinely shipped from fabrication facilities to reactors.

Implications for Arms Control

No true arms-control benefit was obtained by obsessiveness over extended Russian production of degraded plutonium. In fact, this type of obsessiveness has probably contributed to the impasse over international agreement on fissile-material production controls. If gradual and commonsense demilitarization were understood to be a viable option, it is possible that considerably more progress would have been made in a fissile-production cutoff.

As for deep cuts in nuclear arsenals, either unilaterally or by agreement, obstructionist responsibility can also be laid partially at the doorstep of those who, without substantive technical foundation, have exaggerated the risks of demilitarization.

These topics are addressed in the companion Knol (Part 4) on “obdurates.” Hypothesized and amplified fear of proliferation has been partly responsible for prolonging irreversible disarmament. The real threat continues to be the large inventory of devices and materials manufactured to go bang.

Verifiability. Conversion to reactor fuel would go a long way toward paying indigenous MOX facilities which were subject to materials-balance assay in each of the major nuclear weapons states. The verification assay could be conducted by indirect means, such as through subcritical-reactivity measurements. Reactivity measurements are less sensitive to the configuration and more sensitive to the total mass of a piece of uranium or plutonium, which makes measurements likely to be sufficiently sensitive without divulging weapons-design details.

Irreversibility. It was not until the NAS heightened its priority for irreversibility as an criterion for demilitarizing weapons plutonium that they were able to sort through alternative technologies for “dispositioning.” Eventually NAS overcame earlier “authoritative” dismissals of isotopic demilitarization, which is the most irreversible technological barrier to treaty breakout. In coming to this realization, a schism took place among colleagues who conscientiously support the objectives but dispute the means for retaining significant nuclear reductions.[18]

References for Demilitarization Controversy

1. J. Carson Mark, "Reactor-Grade Plutonium's Explosive Properties," Nuclear Control Institute, (August 1990).

2. J. C. Mark, "Explosive Properties of Reactor-Grade Plutonium," Science & Global Security,

Vol. 4 (1993).

3. W. Panofsky, "No quick fix for plutonium threat," Letter, Bulletin of the Atomic Scientists (Jan./Feb. 1996).

4. A. DeVolpi, "Weapons Plutonium Disposition: MOX Gets Go Ahead; Immobilization Dead in Water" Physics and Society, Vol. 31, No. 1 (Jan. 2002).

5. J.C. Mark, T. Taylor, E. Eyster, W. Maraman, J. Wechsler, "Can Terrorists Build Nuclear Weapons?"<http://www.nci.org/k-m/makeab.htm>

6. William J. Broad, "Plutonium is less stable than thought, raising concern about aging weapons," San-Diego Union-Tribune (26 Jan. 2000).

7. A. DeVolpi, "Denaturing Fissile Materials," Progress in Nuclear Energy, Vol. 10 (1982); "Fissile Materials and Nuclear Weapons Proliferation," Annual Reviews of Nuclear and Particle Science, 36:83-114 (1986).

8. A. DeVolpi, Proliferation, Plutonium and Policy: Institutional and Technological Impediments to Nuclear Weapons Propagation, Pergamon, New York (1979).

9. National Academy of Sciences, "Management and Disposition of Excess Weapons Plutonium," National Academy Press, Washington, DC (1994).

10. National Academy of Sciences, (1994) op cit.

11. Committee on International Security and Arms Control, National Academy of Sciences, "Interim Report for the U.S. Department of Energy by the Panel to Review the Spent-Fuel Standard for Disposition of Weapons Plutonium" <http://national-academies.org> (July 1999).

12. A.D. Rossin, "Secrecy and Misguided Policy," paper presented at GLOBAL 2001 Conf., Paris (11 Sept. 2001).

13. B. Pellaud, "Proliferation Aspects of Plutonium Recycling," J. Nuclear Materials Management (Fall 2002).

14. B. Pellaud. op cit.

15. A. DeVolpi, "Fast Finish to Plutonium Peril," Bulletin of the Atomic Scientists (Sep./Oct. 1996).

16. M. Miller and F. von Hippel, "Usability of Reactor-grade Plutonium in Nuclear Weapons," Physics and Society, Vol. 26, No. 3 (July 1997).

17. W. Seifritz, "The preignition problem in nuclear explosive devices (NEDs) for a signoidal Rossi-alpha and a high neutron background," Kerntechnik 72:5 (2007); G. Kessler, W. Hobel, B. Goel, W. Seifritz, "Potential nuclear explosive yield of reactor-grade plutonium using the disassembly theory of early reactor safety analysis," Nuclear Engineering and Design 238: 3475 (2008); W. Seifritz, "A simple excursion model of a nuclear explosive device," Nuclear Engineering and Design, in press (2008); G. Kessler, C. Broaders, W. Hoebel, B. Goel, D. Wilhelm, "A new scientific solution for preventing the misuse of reactor-grade plutonium as nuclear explosive," Nuclear Engineering and Design 238:3429 (2008).

18. My File: NWP3.controversy.014.wpd November 22, 2008.

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NUCLEAR WEAPONS PROLIFERATION: Controversy About Demilitarizing Plutonium - a knol by Alexander DeVolpi

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