UK Nuclear Power Station Fallout map

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I think it would be different than Chernobyl

Chernobyl was due to some idiot pushing safety checks to the limit and and bad design than resulted in the back up generators not starting quick enough if I remember rightly. Since then reactor safety has improved massively and if the lights went out a lot of the reactor in the world would instantly go to back up power and instantly start pulling the fuel rods out of the reactor.

the big concern to me would be decades down the line when the fuel rods corrode and material is released coupled with the decay of the reactor core and buildings. If a reactor did go bang then prevailing winds would have a massive impact as note by LS the range of the fall out from Chernobly is very large globally and the fallout from the Windscale fire in the 50's is thought to have made it to Scandinavia