Japan rates nuclear crisis at highest severity level

TOKYO — Japanese authorities on Tuesday raised the severity rating of the nuclear crisis at the Fukushima Daiichi power plant to the highest level on an international scale, on a par with the 1986 Chernobyl disaster.

Officials from Japan’s nuclear agency reclassified the ongoing emergency from Level 5, an “accident with off-site risk,” to Level 7, a “major accident.” The reassessment comes at a time when the International Atomic Energy Agency says the plant is showing “early signs of recovery” but is still in critical condition.

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Japan raised the crisis level at its stricken nuclear power plant to 7, the highest on an international scale and on a par with the 1986 accident at Chernobyl. (April 12)

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• Japan rates nuclear crisis at highest level

At a news conference in Tokyo, Hidehiko Nishiyama, the chief of Japan’s Nuclear and Industrial Safety Agency, emphasized that radiation released from Fukushima amounted to one-tenth the total released from Chernobyl. But the plant continues to spew radiation, and at a separate news conference, an official from the Tokyo Electric Power Co. said that “our concern is that the amount of leakage could eventually reach that of Chernobyl or exceed it.”

The stark assessment reinforced the sense that this nuclear emergency ultimately will cause problems that exceed those first predicted by the government, which has downplayed long-term safety concerns and only Monday expanded its mandated 12-mile radius evacuation zone.

Still, the upgraded severity reading does not reflect a recent deterioration at the plant. Rather, it suggests Japan’s evolving understanding of the damage that occurred there one month ago — and the contamination that has been leaking ever since.

“We are taking this extremely seriously,” Tokyo Electric said in a statement signed by its president, Masataka Shimizu. “We deeply apologize for tremendous concerns and inconvenience we are causing the residents in the neighboring areas of the power plant as well as people of [Fukushima] prefecture, and further, to the people of” Japan.

A Level 7 accident, according to the International Nuclear and Radiological Event Scale (INES), is typified by a “major release of radioactive material with widespread health and environmental effects.” That measuring scale was established by the IAEA some 21 years ago, but its guidelines leave plenty of room for interpretations, nuclear experts say.

According to the Kyodo News agency, Japan’s Nuclear Safety Commission issued a recent report claiming that the Fukushima plant, at one unspecified point after the March 11 earthquake and tsunami, had been releasing 10,000 terabecquerels of radioactivity per hour. A release of tens of thousands of terabecquerels per hour corresponds with the leakage level that the IAEA recommends as a minimum benchmark for a Level 7 accident.

“This corresponds to a large fraction of the core inventory of a power reactor, typically involving a mixture of short- and long-lived radionuclides,” an IAEA document says. “With such a release, stochastic health effects over a wide area, perhaps involving more than one country, are expected.”

Most radiation readings around Fukushima have been decreasing for several weeks now, but the plant still faces numerous risks. Thousands of tons of contaminated water has flooded key buildings adjacent to the reactors. Nitrogen gas is being injected into one unit to prevent another explosion.