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…

Commentary Decades ago, a single energy disaster left three million acres of land uninhabitable to humans and killed between 85,600 and 240,000 people. A casual student of history might assume these shocking statistics refer to the Chernobyl nuclear accident, but that would be incorrect. No, this catastrophic specter was the fault of the Banqiao Dam collapse in…