Japan's habitable area according to [1] is about 125k sq Km. Fukushima official Exclusion Zone is about 370 sq km [2] - so that's 0.3% which is quite a significant loss in itself.

However given the events, there's a lot of migration out of the surrounding towns and villages outside the exclusion zone due to fear of radiation amd a very marked population decline in the region. Young families don't want to risk raising children in such an area - so the population effects are significantly amplified and towns will go desolate as the older folks who stay pass away.

[1] https://www.gdrc.org/uem/footprints/tokyo-fprint.html

[2] https://blog.japanwondertravel.com/report-of-fukushima-exclu...

[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4199020/

It's planned to reopen in 2030, although parts are open now I believe. Personally I think a better solution would be a nature reserve.

If I were choosing somewhere to live, I'd be more worried about the risk of another tsunami which killed 20,000 people than low level background radiation, same with Earthquakes in California, or Tornados in the middle of the US, or Hurricaines in the South East of the US.

Many places in the exclusion zone are about as radioactive as Cornwall, and people pay a premium to live there. There are far more radioactive cities in the world.