Japan nuclear disaster rose to Level 7 - highest level possible, on a par with Chernobyl

The equivalent of a radiation leak of over ten thousand terabecquerels per hour of iodine 131 is the recommended IAEA boundary for Level 7 accidents. Recent calculations showed that radiation levels at Fukushima reached, at a certain moment on March 11, about 10,000 terabecqerels per hour. Thus the severity of the accident was reclassified today at the same level with Chernobyl catastrophe 25 years ago.

Experts consider that from the very beginning the Japanese authorities knew that the severity of the accident should be raised at Level 7, but delayed the bad news on purpose, not to increase panic.

A Level 7 on the International Nuclear and Radiological Event Scale (INES) means a major accident, with repercussions way beyond the initial Level 5 ranking reported at Fukushima on March 18.

The INES scale starts from Level 0 (deviation with no safety significance), goes through Level 1 anomalies, Level 2 and 3 (incidents and serious incidents), reaching more severe stages of Level 4 and Level 5 accidents – without/with significant off-site risk, Level 6 serious accidents and finally the Level 7 major accidents - the highest on this scale.

Level 7 accidents suppose such a release of radiation that results in the possibility of acute health effects on site, delayed health effects over a wide area, possibly involving more than one country and long-term environmental consequences.

The good news is that radiation released at Fukushima is only 10% of the total released from Chernobyl and is decreasing for several weeks now, while the situation is steadily stabilizing. No deaths directly connected with radiation leaked at Fukushima have been reported so far.

Only three of Fukushima’s six units sustained core damage (reactor 1, 2 and 3) and they all had been given on March 18 a Level 5 rating. At the same time a Level 3 rating was given to unit 4, classification that still stands. As renewed calculations of the radiation released in Japan continue, change in present rating may appear in the near future.