So called Mayak complex, the most secret installation in Chelyabinsk region, maybe even in all Russia. The most contaminated place on whole planet. For compare, in Chernobyl there were 50 million curies* (*unit of radioactivity). In Mayak complex are more than billion curies. And thats a difference more than 200 times of the concentration of radioactivity.
Check out this 30min documentary.