Chronology of Explosions at Fukushima Daiichi Nuclear Plant

Friday, March 11, a 9.0-magnitude earthquake and a 250 mile long tsunami slams into Japan.

Saturday, March 12, a hydrogen is explosion at reactor No. 1 building.

Monday, March 14, a hydrogen explosion at reactor No. 3 building.

Tuesday, March 15, a hydrogen explosion at reactor No. 4 building.

Tuesday, March 15, a hydrogen explosion at reactor No. 2 did not destroy the building.

 Reactors No. 5 and No. 6 were in cold shutdown for planned maintenance

[Yale Environment 360, 3/21/2011, Wiki)