Most of the problems are at Fukushima Dai-ichi I, which had three active units:
Unit 1: BWR-3, 460 MW, activated 1970
Unit 2: BWR-4, 784 MW, activated 1974
Unit 3: BWR-4, 784 MW, activated 1976, MOX fuel
BWR = Boiling Water Reactor
Fukushima Dai-ichi has another 3 units that were shutdown prior to the earthquake and are not a concern to this crisis.
Unit 3 is loaded with mixed-oxide fuel. (MOX)
(Some reports say it is unit 2.)
Three other plants, Fukushima Daini II, Onagawa, and Tokai had less severe problems, but their conditions are improving. An evacuation order is in effect around Daini.
