Ukraine is commemorating the 40th anniversary of the Chernobyl nuclear disaster on Sunday amid lingering fears that Russia's 4-year-old war could spark a repeat of the world's worst nuclear disaster. "The Chernobyl disaster was the result of a reactor experiment ordered by Moscow, in violation of safety protocols, and followed by lies and cover-ups," Ukraine's foreign ministry said in a statement. "To this day, the world has to face consequences brought by a totalitarian system that subordinated truth and science to ideology and political power." Millions were exposed to radiation, hundreds of thousands forced to flee, and wide swaths of...