How bad is the nuclear crisis in Japan?

Fukushima Dai-ichi nuclear complex
In this image released by Tokyo Electric Power Co., smoke billows from the No. 3 unit among four housings cover four reactors at the Fukushima Dai-ichi nuclear complex in Okumamachi, Fukushima Prefecture, northeastern Japan, on Tuesday, March 15, 2011. Japan ordered emergency workers to withdraw from its stricken nuclear complex Wednesday amid a surge in radiation, temporarily suspending efforts to cool the overheating reactors. Hours later, officials said they were preparing to send the team back in.
AP Photo/Tokyo Electric Power Co