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University of Tennessee, Knoxville, Governor’s Chairs are speaking out about the evolving nuclear situation in Japan.

Brian Wirth
Brian Wirth

Brian Wirth, Governor’s Chair for computational nuclear engineering, lauded Japanese officials for their handling of a potentially catastrophic situation.

“Although there is still significant cause for concern, the situation appears to have been well handled by the Japanese utility, nuclear engineers and regulators,” said Wirth, who leads a number of research projects funded by various U.S. Department of Energy offices to investigate the performance of nuclear fuels and structural materials in nuclear environments.

Monday morning, Wirth said the release of radioactivity into the atmosphere is certainly unfortunate, but the magnitude of the release was actually very low and comparable to the additional radiation that airline flight crews receive from cosmic radiation by flying at high altitudes without the benefit of shielding that radiation from the atmosphere.

“The Japanese government has distributed potassium iodide pills to protect the thyroid gland from uptake of radioactive iodine, which is an appropriate precaution based on the lessons learned from the Chernobyl accident, where the Soviet government did not distribute this in a timely fashion. But I want to stress that the magnitude of the radioactive release is much, much smaller than at Chernobyl, and in my opinion, the Japanese government is taking a prudent, preventative measure,” said Wirth.

Howard Hall, Governor’s Chair for global nuclear security, said he understood how the situation in Japan could negatively influence people’s perception of nuclear energy, but it should not.

“What people need to realize is what is happening in Japan is unprecedented for a reactor complex, and that it was contained as it was designed to do,” said Hall. “Unlike Chernobyl, very little radiation material was released and it looks like the Japanese government is handling it very well in a completely devastating situation, where they are still dealing with aftershocks greater than 6.0 that have crippled Japan’s infrastructure.”

Howard Hall

Based on preliminary information Sunday, Wirth explained what caused the radioactive releases:

“The basic scenario as I understand it, is that the reactors all shut down immediately at the time of the earthquake, as they were designed to do. However, even when the nuclear chain reaction is no longer self-sustaining, there is a substantial amount of radioactive decay heat that has to be removed from the reactor core. The reactors are all designed to have multiple, redundant safety systems to continue to cool the reactors to remove this decay heat, including multiple on-site diesel generators designed to provide power to the cooling water pumps. However, the subsequent tsunami damaged the diesel generators, and I have heard that the tsunami may have carried away the diesel tanks. The reactors have batteries to provide backup power in such cases, and these functioned as designed until the batteries ran out.

“Unfortunately, the widespread destruction led to the situation where it was difficult to restore power to the cooling water pumps after the batteries were drained. This did result in insufficient cooling that has caused some uncovering of the fuel rods and release of hydrogen gas resulting from chemical reactions between the cooling water and zirconium fuel cladding materials and some apparent release of radioactive fission products from the fuel pins. This causes a buildup of pressure inside the reactor building, and TEPCO (the Japanese utility) has vented this gas outside of the reactor building at Fukushima Daiichi Units 1 and 3.”

Wirth explained the buildup of hydrogen gas between the outside wall of the steel containment vessel and the concrete building is apparently what caused an explosion at units 1 and 3. The steel containment vessel and the reactor pressure vessel inside the containment were not damaged and functioned as designed. Power has been restored to the cooling pumps, and the Japanese have been very proactive in using any and all available options to keep the reactor cores cooled, including using seawater.

According to Wirth, the Japanese reactors are similar to the ones in the U.S. They are manufactured by General Electric, went into operation in the early 1970s, were designed to withstand a 7.0 earthquake and actually did function as designed immediately following the earthquake. It was the sequence of events, including the tsunami, that caused the subsequent problems with the decay heat cooling removal.

Wirth is unsure of how the events in Japan will impact the nuclear energy renaissance in the U.S.

“There will clearly be a loud group of anti-nuclear activists calling for the end of nuclear power. At this point, I think that a pragmatic view will end up making the conclusion that the reactor accidents will end up as a very significant economic disaster and that any immediate or latent death toll will be dwarfed by the direct loss of life from the tsunami,” said Wirth.

Wirth and Hall are keeping a close eye on the situation in Japan as it continues to change.