Mary and Joseph! what next?
Kyodo News - the fastest update on developments.
Japanese have been struggling to cool the reactors down. Basically, the sequence of events has been as follows: quake made the reactors to shut down - graphite rods were downed and the chain reaction slowed. It means that reactors were kept at the heat production level of 5-6%.
Tsunami flooded the basement and the secondary power supply (diesel generators) was lost along with the cooling system.
Reactors began to heat up and release hydrogen. The first detonation occurred at the reactor no. 1 when a sufficient amount of hydrogen accumulated under the roof and self-detonated when mixing with air.
At this stage Japanese began to pump sea-water into the cooling system of reactors - it was an utter emergency measure, and it means that all three reactors will have to be decommissioned in any outcome. As the sea water heats up, the steam needs to be gradually released to the atmosphere.
The second explosion occurred when the rector no. 3 was left for several hours without cooling and began to emit hydrogen.
The third and foruth explosions occurred when the cooling systems of reactor no. 2 and no. 4 failed. However, the latest detonations are worse as one of them seems to have ruptured either the cooling system or safety container around the reactor leading radiation to leak.
The worst case scenario #1 is when the cooling is lost at any of the reactors, and it begins to collect hydrogen and other gasses inside - then the explosion could rupture the reactor and cause Chernobyl. Scenario #2 is when the cooling is lost, the nuclear fuel begins to burn and melts through the reactor (nothing could contain burning uranium).
Apparently, Japanese are literally fighting for survival now. Sea water was an improvisation and emergency measure, but it seems they would have to keep improvising and charting the unknown.