During the earthquake, reactors stopped automatically, blocking thechain reaction. Backup systems allowing their cooling started. But the tsunami which followed destroyed these systems. Since, the engineers and the technicians who pilot reactors fightfor cooling them and mastering the pressure in the surrounding walls of seclusion and the tanks, two imperative to be followed during such an accident.
Actually, the external powersupplies were connected in four reactors, but the supply was not started up yet. The heart of reactors is partially damaged. The injection of sea water in tanks would be maintained toassure the cooling of hearts. The reactor 1 remains in overheating, and reactors 2 and 3 are still in a critical state. But the risk of a nuclear chain reaction would be very low.Control rooms are very radioactive, limiting the time of presence of the participants. Finally the radioactivity in the air is without danger, but it is now very controlled by severalcountries.
In my opinion, I think that further to the events of Japan. Nuclear power plants should be closed when there would not be dangerous anymore. Japan should relocate hispower plants on a continent, because natural disasters are too important in this country. And finally, nuclear power plants should be situated in places isolated far from the population.