TOKYO — Japanese authorities raised Tuesday their rating of the severity of the Fukushima Daiichi nuclear crisis to the highest level on an international scale, equal to that of the 1986 Chernobyl disaster.
Officials with Japan’s Nuclear Safety Commission 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 still in a critical condition.
The plant’s debilitated reactors face constant threat of strong aftershocks, and the latest on Tuesday morning — a 6.2-magnitude temblor — caused a brief fire at a water sampling facility near Daiichi’s No. 4 reactor. The Tokyo Electric Power Co., which operates the power plant, said that the critical process used to cool the hot fuel rods had not been interrupted, and radiation levels showed no signs of change.
A level 7 accident, according to the International Nuclear and Radiological Event Scale, is typified by a “major release of radioactive material with widespread health and environmental effects.”
[…] Radiation leaking from Fukushima Daiichi amounts to about 10 percent of that from the Chernobyl accident, a Nuclear Safety Commission official, who was not named, said on national television.
[…] According to the Kyodo news agency, Japan’s Nuclear Safety Commission reported Monday that the plant, at one point after the March 11 earthquake and tsunami, had been releasing 10,000 terabecquerels of radioactivity per hour. The report did not specify when those radiation readings occurred. A release of tens of thousands of terabecquerels per hour, though, correspondents with the radiation leakage level that the IAEA uses 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.”
And of course, we are still avoiding the world “meltdown” — although, according to Rep. Ed Markey, the nuclear core has already melted through the reactor vessel.