Before 1986 there have been twelve "public" core meltdowns, and at least six, likely more, incidents not public on nuclear subs, etc.

~ https://en.wikipedia.org/wiki/Nuclear_and_radiation_accident...

You should look up how many live armed nuclear bombs have been accidentally dropped on mainland US soil.

More significantly, there's been a lot of above ground and atmospheric tests that have draped residuals across the planet, and a bunch of dirty Russian / former USSR sites that drift trace across Europe.