A Soviet-era top secret object Duga, an over-the-horizon radar system once used as part of the Soviet missile defense early-warning radar network, seen behind a radioactivity sign in Chernobyl, Ukraine, on Nov. 22, 2018. Among the most worrying developments on an already shocking day, as Russia invaded Ukraine on Thursday, was warfare at the Chernobyl nuclear plant, where radioactivity is still leaking from history's worst nuclear disaster 36 years ago. (AP Photo/Efrem Lukatsky, File)