Nuclear accidents can involve X-ray equipment, radioactive isotopes, particle accelerators, nuclear fuel production plants, nuclear power plants and atomic and hydrogen bombs. Some accidents threaten public health, contaminate crops and animals and could destroy the country side for hundreds of square kilometres. There have been more accidents involving nuclear weapons or reactors than the authorities have officially admitted.
It is extremely difficult to predict exactly what kinds of accidents will occur and thus build in safeguards. All major nuclear accidents in the USA have involved events completely unforeseen in any detailed government study of reactor safety. Furthermore, operator error is likely to play a major role in future accidents.
The 1986 Chernobyl explosion played a critical role in opening up admissions of previous disasters in the former Soviet Union: the secret dumping of millions of tonnes of highly radioactive waste in the River Techa since the early 1950's by a plutonium plant -- 2.75 million curies of waste, equivalent to half the fallout from the bomb that fell on Hiroshima, some tens of kilometres upstream of drinking and bathing water supplies of unknowing villagers; a series of accidents at a plutonium-producing plant near the southern Urals city of Chelyabinsk between 1948 and 1967; a waste storage tank which exploded at the Mayak plutonium plant in 1957, releasing 20 million curies of radiation; a decade later a drought dried up nearby Lake Karachai which had been used as a reservoir for 120 million curies of waste products. Winds scattered radioactive dust over a wide area.