People light candles placed in the form radioactive symbol in Kiev, Ukraine on Thursday. Ukraine marked the 21st anniversary of the deadly explosion at the Chernobyl nuclear power plant, the world's worst nuclear disaster. The April 26, 1986 explosion at the Chernobyl nuclear power plant affected about 3.3 million Ukrainians, including 1.5 million children, according to Ukraine's Chernobyl Union report. (AP Photo/Efrem Lukatsky) Efrem Lukatsky