The International Atomic Energy Agency said it was informed by Japanese authorities that the fire took place at a storage pond for spent fuel rods at the plant's number 4 unit, and that radioactivity was released directly into the atmosphere at dose rates equivalent to 4,000 chest X-rays every hour.
http://www.voanews.com/english/news/asia/east-pacific/Dangerous-Radiation-Levels-Reported-at-Japans-Stricken-Nuclear-Plant-117995699.html
Concern is particularly high regarding the plant's number 2 unit, where officials say coolant boiled away faster than it could be replaced Monday, leaving the fuel rods exposed to the air at least twice. That permits the rods to become extremely hot and begin melting, with the risk of damaging the surrounding containment chamber that keeps deadly radiation from escaping into the environment.
In a nationally televised statement Tuesday, Prime Minister Naoto Kan said the radiation level is "very high" and that there is a
high risk of more radiation escaping. Anyone living within 30 kilometers of the troubled Fukushima nuclear plant has been urged to remain indoors.
nuclear plant explosions and radiation activity