Kyodo News and NHK World are both reporting that Fukushima reactor number 4 is on fire. But ignore the category tag, and like Golob said, don't panic; there's no chance of a core meltdown in this reactor, because it was shut down and had no fuel at the time of the earthquake and tsunami.

So how'd it catch on fire? Well, the speculation is that spent fuel stored within the reactor container may have lost coolant, causing a hydrogen explosion, so you know what...? Maybe you should panic a little after all.

No, strike that, as Golob and others have pointed out, there's no chance of this being a Chernobyl-type disaster due to the design of the reactor, so it's not like we should be getting a radioactive cloud heading toward Seattle. Then again, if you're anywhere within 30 kilometers of Fukushima, panic, because the Japanese government is now reporting radiation being detected there at "dangerous levels" of 400 mili sievert and rising.