Here's a little more reportage on why the Japanese watchdog agency upgraded the status of the incident at Fukushima-1 to 7 (from Al Jazeera):

"Local news agency Kyodo said the government's Nuclear Safety Commission had estimated that at one stage the amount of radioactive material released from the reactors in northern Japan had reached 10,000 terabequerels per hour for several hours, which would classify the incident as a major accident according to the INES scale.

The International Nuclear and Radiological Event Scale (INES), published by the International Atomic Energy Agency, ranks nuclear incidents by severity from 1 to a maximum of 7.

Kyodo did not say when the big increase in radiation had happened but quoted the commission as saying the release had since fallen to under one terabecquerel per hour."

I believe the 10,000 terabequerels per hour readers happened at the end of the first week after the "hydrogen explosion" in Unit 3. Of course the readings are most likely crude estimates because the regular recording instruments were either damaged by explosions or off-line. The Union of Concerned Scientists has a discussion of the radiation releases that merits review.

Charley Noble