Re: Wasn't Fukushima a "fail-safe" design?
Fission ceased at the Fukushima reactors pretty much as soon as the earthquake was detected onshore. The problem was residual heat from the decay of short-lived radioactive fission products in the fuel rods -- when running at full power reactors 2 and 3 generated about 2500MW of heat (reactor 1 was a bit smaller and produced less heat and electricity). After fission ceased the heat output from radioactive decay was about 50MW. When the cooling systems shut down due to loss of external power the cores overheated from that decay energy, not from fission.
A good rule of thumb in the metal foundry business is that 1MW will melt 1 tonne of steel if it is well-insulated so 50MW is a considerable amount of heat energy.
Biting the hand that feeds IT
