Though the Fukushima crisis now stands alongside Chernobyl on the INES event rating, experts note several important distinctions. No deaths have yet resulted from radiation leaked at Fukushima. At Chernobyl, a single reactor exploded, and a massive cloud of cesium, plutonium and strontium spread across Belarus, Ukraine, Russia and Europe. At Fukushima, workers have struggled to stabilize seven reactors and spent fuel pools, but so far the radioactive releases have come as byproduct of emergency cooling efforts, with the venting of radioactive steam and the leaking of contaminated water.
Technically, Japan’s reassessed severity rating applies to only three of Fukushima’s six units — Nos. 1, 2 and 3, which have all sustained core damage. Each of those units, on March 18, had been initially given a Level 5 rating. At the same time last month Japan gave a Level 3 rating to unit 4; that remains unchanged. The IAEA cautioned that Japan could still change its ratings as more information becomes available.
The latest reevaluation underscores the difficulty of measuring the amount of contamination released and the danger it poses. Rather than creating a hard “no-go” circle around the plant, the government has instead singled out five particular towns between 12 and 19 miles from the plant for mandatory evacuation. Residents there should leave within a month, the government said.
Those who stay are at risk of receiving more than 20 millisieverts of radiation in a year — the government’s baseline for evacuations. Exposure at that level doesn’t cause immediate sickness, but it raises risk for cancer and other long-term health problems.
Japan’s various nuclear regulatory groups have come up with widely differing numbers regarding the total contamination released into the environment.
The Nuclear and Industrial Safety Agency, for instance, says that 6,000 terabecquerels of cesium-137 have been released. Japan’s Nuclear Safety Commission, meanwhile, quotes a number twice that. Much of that contamination, though, was released in the first week after an earthquake and tsunami knocked out Fukushima Daiichi’s primary and back-up power supplies, stopping the cooling of the reactors’ cores.
“Monitoring data available shows that, in my view, the government probably knew around March 16, 17 or 18 that it would reach Level 7,” said Hironobu Unesaki, a professor at the Kyoto University Research Reactor Institute. “I just don’t understand why it took them so long to raise the level to 7. They were completely slow. ... Their response has been extremely regrettable. The government is being very careful not to cause unnecessary panic, but they are being too cautious.”
Special correspondent Akiko Yamamoto contributed to this report.
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