After the Japanese earthquake, an American friend living in Tokyo shared some of his reactions about the Fukushima nuclear reactor disaster. The information Dave Brauer shared came from his sources in Japan as well as his personal knowledge of the situation. Since the U.S. has 23 reactors of a design similar to Fukushima, I thought it might help to share some of this information about how these reactors work and what our own risks might be going forward.
There are a number of serious drawbacks of conventional Boiling Water Reactors like the ones in Fukushima.
According to Dave:
The fuel is uranium oxide, 97% of which is U-238 and 3% U-235 (useful for making bombs), which is encased in zirconium tubes. Used fuel rods contain about 5% fission products, including about 1% very long lived products, mostly plutonium. The heat from the uranium fission decays quite rapidly, but the 4% of shorter lived, highly radioactive fission products continue to generate significant heat for weeks and months. If the rods are partially or fully uncovered, at around 1000 degrees steam interacts with the zirconium cladding to form hydrogen. Worse still, if the temperature reaches 1100, then the reaction becomes self-sustaining. There is no oxygen inside the containment vessels. However, the operators (of the Fukushima reactors) have had to periodically release steam, containing the hydrogen. This collected in the reactor buildings in #1 and #3 causing explosions. These were more cosmetic than serious. The highest concentration of fission products are contained within the zirconium cladding. At 1200 degrees C, the zirconium melts. Melting fuel rods will expose the fission products, some of which are volatile, into the environment.
The surprising and disturbing event in Fukushima was the hydrogen explosion in reactor #4.
This reactor was cold, with the fuel assembly unloaded. On March 15th at 6am, there was a hydrogen explosion in #4. This could only have been due to a partial drying of the spent fuel rods in the cooling pool above the containment vessel. Since electricity to run the pumps to keep water circulating in the cooling pools had been cut off to all the reactors since the 11th, the prospect of further hydrogen explosions and spent fuel rods melting, releasing their fission products, has been extremely worrying.
As the Japanese military helicopters desperately tried to dump water from bladders on to reactor #3, it really looked like the situation was spiraling out of control. However, by the 18th of March, they had started firing many tons of water at the roof of #3 using advanced fire trucks. The radioactivity went down. The tenor of the reporting in Japan calmed down. Reactors #2, #3, and #5, had switched back to electrical pumping systems by the 26th of March, as well. So the reactors are being brought back under control bit by bit.
Dave notes that as worry over a large release of radioactivity reaching the Tokyo metropolis has receded, concern is shifting to the effects of the relatively small amounts of radiation reaching other prefectures and Tokyo, and the contamination in the 40km region surrounding the plants.
Radioactive Iodine-131 and Cesium-137 (also producing gamma and beta radiation) have been found in vegetables grown in Fukushima. The amounts were over the limits of 500 becquerels of cesium-137 per kg, and 2000 becquerels of iodine-131 per kg. One sample had 82,000 becquerels per kg, which sounds terrible, but if you ate 1 lb of the leafy green vegetable in question, you would get 1uSv or 0.001 of your yearly allowance in Japan. The government is reimbursing farmers for destroying crops certified as contaminated. One poor farmer with 600kg of tomatoes grown indoors, and so uncontaminated, and therefore not eligible for reimbursement, had to destroy his crop because no one would buy Fukushima produce.
While the U.S. government told its citizens living in Japan to evacuate from a 50 mile (80 km) radius of the plant, the Japanese government recommended that residents in the 20-30km zone evacuate voluntarily because it was very difficult to provide daily necessities, and there was the possibility that a mandatory evacuation order might become necessary. This turned out to be more difficult than anticpated.
Most of the remaining residents are older. There is no gasoline (to transport them), because truck drivers, fearful of radiation, are unwilling to enter the zone... In and around the plants, though the reactor buildings are gradually being brought under control, the immediate environment is much more dangerous and severely contaminated than had been recognized earlier. The employees, who have been risking their lives for the nation for almost 3 weeks, are exhausted and starting to make mistakes.
Some of the mistakes being made include reports of radiation that turn out to be false. But much worse, just a few days ago, 3 workers laying cable in the basement of reactor #3 were working in 15cm of water, which turned out to contain 3.9million becquerels of radiation. One of them had on high rubber boots, but the other two got soaked and suffered burns.
The plant workers are eating two meals a day, sleeping on conference room floors with a single blanket, in a management center building about 300 meters from the reactors. The building is fitted with filters to keep out radioactive particles. Most of the workers are local Fukushima employees, some of whom have been unable to contact their families.
Although residents of Tokyo are experiencing rolling blackouts, and reduced train schedules, this is nothing compared to what the heroes at the Fukushima plant, and the survivors of the earthquake and tsunami are struggling against.
Are there alternatives to the current design of nuclear reactors? Apparently there are newer designs that are safer because they rely less on active intervention to prevent meltdowns, but Dave points out that there are fundamental problems with solid fuel uranium/plutonium reactors. The fuel rods must be removed, not when all the fission fuel has been used up, but far earlier, when the zirconium begins to crack from the exposure to radiation, threatening to release radioactive gasses building up in the core.
Furthermore, uranium reactors produce plutonium-239, which is extremely poisonous, in addition to being radioactive, and has a half-life of 24,000 years, meaning it will be around for 240,000 years. By comparison, there is an alternative called "Thorium", which produces much smaller quantities of transuranic elements, and these are readily separated in the liquid reactors being proposed. This Wired article makes the point that the US was developing both uranium and thorium technologies in from the late 50s through the 70s, but a political decision was made to end the thorium program because uranium fission products, specifically plutonium were useful for making bombs.
There is a small group of activists promoting a return to this thorium technology, which appears to be inherently safer.
While Japan continues to struggle with a resolution to the nuclear reactor disaster, I am happy to report that Dave and his family feel safe in Tokyo and have no plans to leave any time soon.
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