Recent events in Japan have shown us the dangers of nuclear power plants. Once certain conditions exist, the people who build and maintain these plants have virtually no way of preventing dangerous radiation from spreading to the general population.
How a Nuclear Plant Works
To understand what happened in Japan recently, and at Three Mile Island in the U.S. in 1979, and Chernobyl in the Ukrainian SSR in 1986, you first need to know how a nuclear plant works.
Nuclear plants contain one or more reactors. The reactor core sits in the center of the reactor. It contains radioactive fuels, uranium or a mix of uranium and plutonium, in pellet form. These are packed in long tubes made of zirconium metal.
This fuel naturally gets very hot because of the radiation. When immersed in water, it produces steam, which is then used in a generator to produce electricity.
In addition to producing steam, water cools the fuel in the reactor core, keeping its temperature at safe levels.
The reactor core is surrounded by a reinforced structure that contains a dry well and one or more wet wells. This is called the primary containment and serves to keep radiation from escaping into the atmosphere.
The secondary containment is the reactor building itself, which is typically equipped with air filters designed to capture any radiation that may have escaped the primary containment. This provides another level of defense to ensure nothing escapes into the atmosphere.
Nuclear Accidents
Japan's recent earthquakes caused two problems, both of which contributed to the nuclear emergency.
First, the earthquakes were strong enough to cause cracks, fire, and explosions within multiple reactors. This took away any protection offered by the now-destroyed buildings that provided secondary containment for some of the reactors. Some speculation has been raised about cracks in the primary containments as well. These raise serious concerns about the release of radiation.
Second, the pumps that circulated water to cool the fuel rods stopped working. Without cold water constantly running past to remove excess heat, the temperature within the reactor core rises. Soon the water heats up and evaporates. The heat produced by radioactive fuel can heat to where the tubes that hold it blister and rupture. Radioactive material is now released into the reactive vessel that holds the core.
When this happens, relief valves automatically open to release steam from the reactor vessel into the surrounding primary containment. Radioactive material escapes with the steam.
During this time, workers will be doing everything they can to cool the reactor. For example, in Japan sea water was injected into some of the reactors. There were also reports of water cannons being used to deliver water into critical areas. These are all attempts to prevent partial or complete meltdowns.
Partial Meltdown
Fuel that remains uncovered by water, and thus exposed for several hours, will start to melt. Melted fuel drains from pipes and collects on the bottom of the reactor vessel. Left unchecked, the molten fuel can eventually burn its way through the reactor vessel.
Complete Meltdown
Once the fuel melts through the reactor vessel, it drops onto the floor of the primary containment. This chamber is designed to contain the melted fuel and the radiation it emits. However, there is always a chance this will fail. The radioactive emissions cause a buildup in pressure within the containment. Add to that the damage already caused by earthquakes and you can see why Japan has a major emergency.
If reactor vessels are breached and primary and secondary containments are both damaged, dangerously large amounts of radiation can be released into the atmosphere.
The Danger of Radiation
We all live with small amounts of background radiation. When you get x-rays, larger amounts are sent through your body. These and other small amounts of radiation are not harmful. In some cases, radiation can even be used to improve health, for example, in treating certain cancers.
Release of large doses of radiation from a nuclear accident is a different situation altogether. Extreme doses of radiation destroy living tissue. High doses damage tissue, which can lead to birth defects, cancer, and related diseases.
Iodine-131 and Cesium-137 are two of the radioactive isotopes released as a result of a nuclear accident.
Iodine-131 spreads rapidly and is most dangerous immediately following an accident. The human body absorbs this element into the thyroid gland, where it can cause cancer. Iodine-131 has a half-life of eight days. That means its radioactivity drops by half every eight days. After several weeks or months, Iodine-131 will no longer cause new damage because it will no longer be radioactive.
Cesium-137, the second radioactive isotope produced, has a half-life of 30 years. It will take more than a century to decay to the point where its radioactivity will no longer cause harm.
Living organisms treat Cesium-137 the same as they treat potassium, an element that is commonly found in salt. This means that Cesium-137 can be passed through the food chain. You can be exposed to radiation by eating meat or vegetables from organisms previously exposed to this source of radiation. Cesium-137 is known to produce many kinds of cancer.
Can it happen here?
A nuclear accident can happen anywhere a nuclear power plant is in operation.
In the United States, the Nuclear Regulatory Commission (NRC) oversees construction and operation of nuclear power plants. Their website has extensive information, along with names and locations of all nuclear power plants in the U.S.
The Union of Concerned Scientists, an independent organization, also provides information, along with concerns about the use and safety of nuclear power.
Judy Downing is a freelance writer. For more information and tips about safety and emergency preparedness -- and about How to Live the Life You Want, go to http://vapata.com
