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.