If you haven't already heard, there has (apparently) been a criticality accident at the JCO fuel processing plant at Tokaimura, 87 miles northeast of Tokyo. I'll give you some of the details as best as I can, although reports are conflicting and confusing - the BBC seems to have the best coverage at http://news.bbc.co.uk/
Apparently 18 kg of uranium (U-235? In an acid solution?) was added to a tank (mixing tank?) where the maximum allowable addition was 2.3 kg. This occured at 10:35 local time (01:35 GMT) September 30th (19:35 Central time Sept 29th). There is apparently still concern (a "strong possibility") that "abnormal reactions" were continuing - presumably a concern that criticality or near criticality still exists. There was mention (somewhere) of an INES event level 2, but the European NucNet service said IAEA had not yet given a rating.
A blue "flame" (a flash of Cherenkov radiation?) was seen, and at least 14 workers have been taken to hospital. Three were suffering from nausea and diarrhea, apparently from a high gamma and neutron dose, and two of them are in critical condition. Radiation levels were "15,000 times higher than normal just after the accident" (presumably meaning above background radiation), but there wasn't a mention of where the readings were taken. The level was still 4 mR/hr at the boundary of the site, as of about 10 hours ago, and were apparently 10 times background 2 km from the site. More recently BBC reported "Radiation levels nearby were said to have returned to normal after several hours."
150 people have been evacuated from houses nearby, and 300,000 within a 10 km radius have been told to stay indoors.
The details remain sketchy, but that's the best I can glue together at present.
- Morgan Brown