Z. Medvedev is a Soviet dissident and exile that naively mentioned the Kyshtym disaster in an interview not understanding that he would be roundly panned by Western authorities in the nuclear industry and fellow travelers in Western media. Being a legitimate and accomplished academic he valued his credibility so he wrote a book to convince the world, using research papers published by Soviet scientists and available in the open press, that the disaster actually happened. He showed that the work in the papers could only have been conducted given massive radioactive contamination over a wide area, despite deliberate effort to obscure these circumstances. The cited papers would have been blocked from publication had the Soviet censors understood what they were reading, but they didn't, so the evidence accumulated. If anyone in the West noticed prior to Medvedev sticking their noses in it they didn't bother to say anything.
Years later the Soviets fessed up and vindicated Medvedev.
Experts in Britain, the United States, France, and many
other countries responded by denying my story and stating
that such a thing was technically impossible. The earliest
and most sharply worded rebuttal to my story came from the
chairman of the United Kingdom Atomic Energy Authority, Sir
John Hill. His interview with the Press Association
published in the London Times on November 8, 1976, was
reprinted in many European and American papers. He declared
in the most high-handed fashion that my story was "rubbish".
-- Zhores Medvedev, Nuclear Disaster in the Urals, p5