No, that isn't correct. Fukushima (along with every reactor on the eastern half of Honshu) failed into quench, within seconds, exactly as designed, as a consequence of the earthquake rattling a system around the control rods which is intentionally designed to only keep them out of the reactor by continued effort.
All the problems were caused by waste heat, rather than ongoing criticality (which would have produced 20 times the heat and been a much, much scarier proposition for the teams on site).
Let's be more precise here: some of the pebble bed designs offer passive decay heat removal. The PB-AHTR, for example, gets this handy property from its choice of coolant and geometry.
I might be using the term "passive safety" incorrectly, but I wouldn't call a design "safe" if, even after criticality ended, there was still enough heat/pressure to cause explosions that subject nearby people to high levels of radiation.
There's no doubt in my mind that Fukushima is far better designed and in much better operating order than Chernobyl (a terrible comparison for a number of reasons) was.
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No, that isn't correct. Fukushima (along with every reactor on the eastern half of Honshu) failed into quench, within seconds, exactly as designed, as a consequence of the earthquake rattling a system around the control rods which is intentionally designed to only keep them out of the reactor by continued effort.
All the problems were caused by waste heat, rather than ongoing criticality (which would have produced 20 times the heat and been a much, much scarier proposition for the teams on site).
Pebble bed in particular, if I recall, is passively safe precisely because it resists waste heat.
Let's be more precise here: some of the pebble bed designs offer passive decay heat removal. The PB-AHTR, for example, gets this handy property from its choice of coolant and geometry.
I might be using the term "passive safety" incorrectly, but I wouldn't call a design "safe" if, even after criticality ended, there was still enough heat/pressure to cause explosions that subject nearby people to high levels of radiation.
There's no doubt in my mind that Fukushima is far better designed and in much better operating order than Chernobyl (a terrible comparison for a number of reasons) was.