Not just one - but two of 'em.
http://www.cnn.com/2011/WORLD/asiapc...pt=T1&iref=BN1
Chief Cabinet Secretary Yukio Edano told reporters there is a "possibility" of a meltdown at the plant's No. 1 reactor, adding, "It is inside the reactor. We can't see." He then added that authorities are also "assuming the possibility of a meltdown" at the facility's No. 3 reactor.