I have been wondering why they have 4 reactors in the same place.
It would be better to build them farther apart. Also, it sure looks like they built these reactors too close to the ocean. That puts them in the path of a Tsunami caused by an earthquake, and it was the Tsunami wave that knocked out the backup diesel generators and turned this into a major problem. We’ve done the same thing here in the US. Some of out nuclear plants are too close to the ocean and could get hit by a Tsunami wave some day. The company that built these reactors in Japan probably thought the Tsunami threat was too unlikely to fully consider in their design.