On March 11, 2011 at 2:46 PM, an earthquake shook Japan. With a magnitude of 9.0, it did considerable damage on the region. It also caused a tsunami which disabled the power supply and cooling of the 3 nuclear reactors. This caused the 3 reactors to melt. The only way to prevent it from melting was flooding it with seawater but by the time the government ordered to flood the reactors, it was already too late to prevent meltdown.

Reactor 1:

A hydrogen explosion on the Saturday blew off the roof of the reactor as workers worked to cool down the reactor. The primary containment vessel is said to be intact.

Reactor 2:

A hydrogen explosion on Tuesday ruptured and have breached the primary containment.

Reactor 3:

Water injection failed. Reduced RPV pressure by venting steam into the wetwell, allowing the injection of seawater. Venting the suppression chamber and containment was successfully undertaken. On Monday 14th, PCV venting was repeated. It backflowed and a hydrogen explosion took place. Explosion of the containment blew off the roof and walls and demolished the top part of the building. Created a lot of debris and the areas around unit 3 were very radioactive.

Reactor 4:

This reactor was shut down for maintenance before the earthquake. An explosion happened that destroyed the top of the building and damage unit 3’s superstructure further.

Comments:

The information I got these from was kind of confusing to me so if you want a better understanding go down and look at the links.

Sources:

http://www.world-nuclear.org/info/fukushima_accident_inf129.html

http://www.globalpost.com/dispatch/news/regions/asia-pacific/japan/120705/fukushima-daiichi-nuclear-disaster-man-made

http://www.nytimes.com/interactive/2011/03/15/world/asia/daiichi-graphic.html