The Kyshtym disaster was a chemical explosion at a nuclear facility that made weapons grade materials for the Soviets. It blew open a storage tank and heavily contaminated about 800 sq. kilometers. Because of secrecy concerns, people in the path of the radiation were not warned for weeks or months, but eventually some of the worst affected areas were evacuated and remain so now.
Additionally, the reactors at the site did not have a recirculation system, they used lake water in an open cooling system, running the water through the reactor and back into the lake. This resulted in a similar situation to the ongoing Fukushima crisis, where water that had been directly in contact with the reactor core was released, except that it was deliberate and ongoing.
Then they dumped the high level waste in Lake Karachay as a storage solution. It is now so radioactive that being at the shore of the lake would expose you to a fatal dose of radiation in about an hour. Here’s a report with details and doses.
Everybody is exposed to radiation. A little bit more or a little bit less is of no consequence.
–Dixy Lee Ray