By HIROKO TABUCHI, KEITH BRADSHER and MATTHEW L. WALD
Published: March 14, 2011
This article is by Hiroko Tabuchi, Keith Bradsher and Matthew L. Wald.
Toru Nakata/Asahi Shimbun, via Associated Press
A hospital worker was checked for radiation contamination Sunday in Fukushima Prefecture.
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"Each time the diameter of the evacuation circle increases. All of which begs the question: Does the power company actually have any real control over this situation or are they merely babysitting these reactors as things fall apart?"jake, NYC
TOKYO — Japan faced the likelihood of a catastrophic nuclear accident Tuesday morning, as an explosion at the most crippled of three reactors at the Fukushima Daiichi Nuclear Power Station damaged its crucial steel containment structure, emergency workers were withdrawn from the plant, and a fire at a fourth reactor spewed large amounts of radioactive material into the air, according to official statements and industry executives informed about the developments.
“No. 4 is currently burning and we assume radiation is being released. We are trying to put out the fire and cool down the reactor,” the chief government spokesman, Yukio Edano, told a televised press conference. “There were no fuel rods in the reactor, but spent fuel rods are inside.”
Government officials also said the containment structure of the No. 2 reactor had suffered damage during an explosion shortly after 6 a.m. on Tuesday.
They initially suggested that the damage was limited and that emergency operations aimed at cooling the nuclear fuel at three stricken reactors with seawater would continue. But industry executives said that in fact the situation had spiraled out of control and that all plant workers needed to leave the plant to avoid excessive exposure to radioactive leaks.
If all workers do in fact leave the plant, the nuclear fuel in all three reactors is likely to melt down, which would lead to wholesale releases of radioactive material — by far the largest accident of its kind since the Chernobyl disaster 25 years ago.
Reports of an imminent worsening of the problem came after a frantic day and night of rescue efforts focused largely on the No. 2 reactor. There, a malfunctioning valve prevented workers from manually venting the containment vessel to release pressure and allow fresh seawater to be injected into it. That meant that the extraordinary remedy emergency workers have been using to keep the nuclear fuel from overheating no longer worked.
As a result, the nuclear fuel in that reactor was exposed for many hours, increasing the risk of a breach of the container vessel and a more dangerous emissions of radioactive particles.
By Tuesday morning, the plant’s operator, Tokyo Electric Power, said it had fixed the valve and resumed seawater injections, but that they had detected possible leaks in the containment vessel that prevented water from fully covering the fuel rods.
Then the explosion hit the same reactor. The operator initially reported that the blast may have damaged the bottom part of the container vessel, but later said radiation levels had not risen high enough to suggest a major escalation of the problem. While they did not immediately provide a detailed account of what happened at the reactor, government and company officials initially ruled out a serious breach that could lead to massive radioactive leaks or a full meltdown of the nuclear fuel.
Even if a full meltdown is averted, Japanese officials have been facing unpalatable options. One was to continue flooding the reactors and venting the resulting steam, while hoping that the prevailing winds, which have headed across the Pacific, did not turn south toward Tokyo or west, across northern Japan to the Korean Peninsula. The other was to hope that the worst of the overheating was over, and that with the passage of a few more days the nuclear cores would cool enough to essentially entomb the radioactivity inside the plants, which clearly will never be used again. Both approaches carried huge risks.
While Japanese officials made no comparisons to past accidents, the release of an unknown quantity of radioactive gases and particles — all signs that the reactor cores were damaged from at least partial melting of fuel — added considerable tension to the effort to cool the reactors.
“It’s way past Three Mile Island already,” said Frank von Hippel, a physicist and professor at Princeton. “The biggest risk now is that the core really melts down and you have a steam explosion.”
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