KYIV—The Soviet Union knew the Chernobyl nuclear plant was dangerous and covered up emergencies there before the 1986 disaster, the Ukrainian authorities said as they released documents to mark the 35th anniversary of the accident on Monday.
After a botched safety test in the fourth reactor of the plant, located in what was then Soviet Ukraine, clouds of radioactive material from Chernobyl spread across much of Europe in what remains the world’s worst nuclear disaster.
