Both Fukushima & Chernobyl would have been essentially non-issues if built further away from population centers. I know this is Sim City logic: but my answer to that would be: quite a lot!
The Chernobyl Exclusion Zone covers 2,600km². It's irregularly shaped so it's unlikely you can predict which area will actually be irradiated, so a nuclear power plant in fact endangers an even larger area. Good luck finding a place in Europe, let alone Japan, that is far enough from population centers.
Also consider that NPPs need cooling water so they are often located near rivers. As are population centers.
