Question:Why are those 4 reactors in Japan
- two which have had explosions, and an additional one threatening to meltdown - so close to each other?
One one reactor fails, because of the proximity to the others, it presents a significant obstacle to workers trying to keep the remaining ones from failing.
Economies of scale? Having them close together also facilitates emergency work, for example they are pumping in seawater to one site instead of four.
I am not giving an authoritative response, just conjecturing.