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Control of Reactors? Serious Doubts?

16.12.2011

Susanne Gerber

“Claiming a cold shutdown does not have much meaning for damaged reactors like those at Fukushima Daiichi,” said Noboru Nakao, a nuclear engineering consultant at International Access Corporation. In fact, experts point out, damaged fuel cores have yet to be removed from plants that suffered meltdowns decades ago. Some experts said talk of a cold shutdown deflected attention from the more pressing problem of further releases of radioactive contamination into the environment. In particular, they said there was still a danger to the nearby Pacific Ocean from the 90,000 tons of contaminated water that sit in the basements of the shattered reactor buildings, or are stored in fields of silver tanks on the plant’s grounds. “At this point, I would be more worried about the contamination than what’s happening inside the reactors,” said Murray E. Jennex, an expert on nuclear containment at San Diego State University. Mr. Jennex said he believed the government’s claim that the reactors themselves were now stable, and particularly that the resumption of the heat-producing chain reaction called fission was no longer possible. While the discovery last month of the chemical xenon, a byproduct of fission, in one of Fukushima Daiichi’s reactors briefly raised alarms that a chain reaction had restarted, Mr. Jennex said enough of the radioactive fuel had decayed since the accident in March to make that unlikely. Other experts disagreed. Kyushu University’s Mr. Kudo said that the restart of fission, a phenomenon known as recriticality, could not be ruled out until the reactors could be opened, allowing for an examination of the melted fuel. But he and other experts said their biggest fear was that another earthquake or tsunami could knock out Tepco’s makeshift cooling system. They noted that it was not built to earthquake safety standards, and relied on water purifiers and other vulnerable equipment connected to the reactors by more than a mile and a half of rubber hoses. “All it would take is one more earthquake or tsunami to set Fukushima Daiichi back to square one,” Mr. Kudo said. “Can we really call this precarious situation a cold shutdown?”

http://www.nytimes.com/2011/12/15/world/asia/japan-set-to-declare-control-over-damaged-nuclear-reactors.html?_r=1

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Einsortiert unter:Consequences, Danger, Fukushima, Radiation

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