There is also a human element. Unit 1 had been retrofitted with an Isolation Condenser, which is capable of cooling the core and preventing a meltdown without needing the pumps that couldn't run due to lack of power. This is exactly the type of upgrade people often suggest.
Unfortunately, for reasons that are still murky, this system wasn't activated, and Unit 1 melted down. The problems at Unit 1 also contributed to the problems at other units, causing radiation hazards, diverting personnel and attention, etc.
In fact, a larger version of this system is touted as one of the major safety features of the newer AP1000 plants, because all it requires is that you open a couple of valves, and the reactor can be safely shutdown as long as you add water every couple of days. Unfortunately at Fukushima, they didn't open the valves.
All of that said, the absolute damage from the accidents at Fukushima was tiny in comparison to the other damage from the tsunami, and much less than the damage of operating coal plants with no accidents whatsoever in Japan.
Unfortunately, for reasons that are still murky, this system wasn't activated, and Unit 1 melted down. The problems at Unit 1 also contributed to the problems at other units, causing radiation hazards, diverting personnel and attention, etc.
In fact, a larger version of this system is touted as one of the major safety features of the newer AP1000 plants, because all it requires is that you open a couple of valves, and the reactor can be safely shutdown as long as you add water every couple of days. Unfortunately at Fukushima, they didn't open the valves.
All of that said, the absolute damage from the accidents at Fukushima was tiny in comparison to the other damage from the tsunami, and much less than the damage of operating coal plants with no accidents whatsoever in Japan.