Thursday, December 15, 2011







Japan May Declare Control of Reactors, Over Serious Doubts

TOKYO — Nine months after the devastating earthquake and tsunami knocked out cooling systems at the Fukushima Daiichi nuclear plant, causing a meltdown at three units, the Tokyo government is expected to declare soon that it has finally regained control of the plant’s overheating reactors.


But even before it has been made, the announcement is facing serious doubts from experts.


On Friday, a disaster-response task force headed by Prime Minister Yoshihiko Noda will vote on whether to announce that the plant’s three damaged reactors have been put into the equivalent of a “cold shutdown,” a technical term normally used to describe intact reactors with fuel cores that are in a safe and stable condition. Experts say that if it does announce a shutdown, as many expect, it will simply reflect the government’s effort to fulfill a pledge to restore the plant’s cooling system by year’s end and, according to some experts, not the true situation.


If the task force declares a cold shutdown, the next step will be moving the spent fuel rods in nearby cooling pools to more secure storage, and eventually opening the reactors themselves.


However, many experts fear that the government is declaring victory only to appease growing public anger over the accident, and that it may deflect attention from remaining threats to the reactors’ safety. One of those — a large aftershock to the magnitude 9 earthquake on March 11, which could knock out the jury-rigged new cooling system that the plant’s operator hastily built after the accident — is considered a strong possibility by many seismologists.

しかし、多くの専門家が恐れるのは、政府の勝利宣言は事故についての国民の怒りを和らげるためだけのもので、原子炉の安全性を脅かす危険から注意をそらすのではないか、ということである。そんな危険の一つ-3月11日のマグニチュード9の地震の余震で、福島原発の運転者である東電が事故後に応急措置として急いで構築した新しい冷却システムが損傷してしまう -は、可能性が大きいものとして多くの地震学者が指摘する。

They also said the term cold shutdown might give an exaggerated impression of stability to severely damaged reactors with fuel cores that have not only melted down, but melted through the inner containment vessels and bored into the floor of their concrete outer containment structures.


“The government wants to reassure the people that everything is under control, and do this by the end of this year,” said Kazuhiko Kudo, a professor of nuclear engineering at Kyushu University. “But what I want to know is, are they really ready to say this?”


Perhaps to give itself some wiggle room, the government is expected to use vague terminology, announcing that the three damaged reactors are in a “state of cold shutdown.” Experts say that in real terms, this will amount to a claim that the reactors’ temperatures can now be kept safely below the boiling point of water, and that their melted cores are no longer at risk of resuming the atomic chain reaction that could allow them to again heat up uncontrollably.


And indeed, experts credit the operator, the Tokyo Electric Power Company, or Tepco, with making progress in regaining control of the damaged reactors. They say the plant’s makeshift new cooling system, built with the help of American, French and Japanese companies, has managed to cool the reactors’ cores, including the molten fuel attached to the outer containment vessels.


Experts also say a new shedlike structure built over the heavily damaged Unit 1 reactor building has helped cap the plant’s radiation leaks into the atmosphere. The building was one of three reactor buildings destroyed in hydrogen explosions in March that scattered dangerous particles over a wide swath of northeastern Japan.


Still, experts say the term is usually reserved for healthy reactors, to indicate that they are safe enough that their containment vessels can be opened up and their fuel rods taken out. But they warn it may take far longer than even the government’s projected three years to begin cleaning up the melted fuel in Fukushima Daiichi’s damaged reactors. This has led some experts to say that proclaiming a cold shutdown may actually be deceptive, suggesting the Fukushima plant is closer to getting cleaned up than it actually is.


“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.

「福島第1原発の原子炉のような壊れた原子炉に対して冷温停止を宣言しても、さほどの意味はない」と言うのは、International Access Corporationの原子力工学コンサルタントの中尾昇だ。

In fact, experts point out, damaged fuel cores have yet to be removed from plants that suffered meltdowns decades ago. In the case of Chernobyl, Soviet officials simply entombed the damaged reactor in a concrete sarcophagus after the explosion there in 1986. 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.

「現時点では、原子炉の中がどうなっているかよりも汚染の状況の方が心配だ」、というのはMurray E. Jennex、サンディエゴ州立大学の原子力封じ込めの専門家である。

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?”




  1. 翻訳ありがとうございます。






  2. Blue DolphineDecember 18, 2011 at 12:17 PM