The cooling pumps only failed roughly an hour after the quake when the diesel generators were flooded. This hour probably save the plant from a more serious outcome.
The shutdown would have been almost immediate with the start of the quake. After an hour's cooldown the decay heat would only be producing 0.5-1% of the full power level ie. a few hundred kW not MW. Now a day later the decay heat will have reduced even further.
It is extremely unlikely that after this time there would be enough heat to cause any melting of the fuel, only some of the cladding of any rods exposed at the top of the reactor would be in danger of melting. Although this of course is a serious failing.
The pressure would have been released intentionally from the rector vessel circuit to the containment building. Once the pressure in the containment building got too high it could have exploded just from the steam pressure. There is no evidence yet of significant hydrogen buildup. Although the radiation levels of over 1000microseiverts per hour reported a little distance from the plant do suggest some fuel rods have been compromised.
It is also worth mentioning that these old BWR designs are completely different to what would be allowed as new build today. The PWR designs proposed for most new-builds have passive cooling systems, and so do not rely on having cooling pumps powered after a shutdown.
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The cooling pumps only failed roughly an hour after the quake when the diesel generators were flooded. This hour probably save the plant from a more serious outcome.
The shutdown would have been almost immediate with the start of the quake. After an hour's cooldown the decay heat would only be producing 0.5-1% of the full power level ie. a few hundred kW not MW. Now a day later the decay heat will have reduced even further.
It is extremely unlikely that after this time there would be enough heat to cause any melting of the fuel, only some of the cladding of any rods exposed at the top of the reactor would be in danger of melting. Although this of course is a serious failing.
The pressure would have been released intentionally from the rector vessel circuit to the containment building. Once the pressure in the containment building got too high it could have exploded just from the steam pressure. There is no evidence yet of significant hydrogen buildup. Although the radiation levels of over 1000microseiverts per hour reported a little distance from the plant do suggest some fuel rods have been compromised.
It is also worth mentioning that these old BWR designs are completely different to what would be allowed as new build today. The PWR designs proposed for most new-builds have passive cooling systems, and so do not rely on having cooling pumps powered after a shutdown.