There is a difference between a nuclear reactor blowing up in a country with low overall population density (e.g. the US; in Chernobyl also it wasn't that taxing to designate an exclusion zone for a few centuries), it happening in a very densely populate country (where it would be a desaster), or it happening in a military sub where the owning state doesn't care about collateral damage [1]

[1] https://www.theguardian.com/world/2014/jun/19/us-depleted-ur...