I thought this article was reasonably interesting:
You'll see where the UK hots spots are and that the average backgound is a few milliSieverts (mSv) per year. For comparison that xkcd chart at:
tells us that 4Sv (i.e., about 1000 times backgraound), received not in a year but all at once, is usually fatal.
Then there's the Winky article at:
which includes a section on nuclear accidents' contribution to background. It's pertinent enough tp include it all here:
Nuclear accidents
Under normal circumstances, nuclear reactors release small amounts of radioactive gases, which cause small radiation exposures to the public. Events classified on the International Nuclear Event Scale as incidents typically do not release any additional radioactive substances into the environment. Large releases of radioactivity from nuclear reactors are extremely rare. To the present day, there were two major civilian accidents ? the Chernobyl accident and the Fukushima I nuclear accidents ? which caused substantial contamination. The Chernobyl accident was the only one to cause immediate deaths.
Total doses from the Chernobyl accident ranged from 10 to 50 mSv over 20 years for the inhabitants of the affected areas, with most of the dose received in the first years after the disaster, and over 100 mSv for liquidators. There were 28 deaths from acute radiation syndrome.
Total doses from the Fukushima I accidents were between 1 and 15 mSv for the inhabitants of the affected areas. Thyroid doses for children were below 50 mSv. 167 cleanup workers received doses above 100 mSv, with 6 of them receiving more than 250 mSv (the Japanese exposure limit for emergency response workers).
The average dose from the Three Mile Island accident was 0.01 mSv.
End
I wish the likes of T r o l l would learn to do their own research, look at and understand the numbers, and so be in a position to answer their own "What if" questions.