Japan Faces Prospect of Nuclear Catastrophe as Workers Leave Plant

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at the Fukushima Daiichi Nuclear Power Station damaged its crucial steel containment structure, emergency workers were withdrawn from the plant, and much larger emissions of radioactive materials appeared immiment, according to official statements and industry executives informed about the developments.

Japanese Prime Minsiter Naoto Kan made a televised address to the nation at 11 a.m. Tokyo time to discuss the latest developments in the crisis.

The sharp deterioration came after government officials said the containment structure of the No. 2 reactor, the most seriously damaged of three reactors at the Daichi plant, 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 escalatiion 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.”

Hiroko Tabuchi reported from Tokyo, Keith Bradsher from Hong Kong and Matthew L. Wald from Washington.

via nytimes.com