Ukraine’s Zaporizhzhia nuclear power plant was built during the Soviet era and is one of the 10 biggest in the world. Concerns of a possible nuclear catastrophe have grown after the plant became engulfed by fighting between Russian and Ukrainian troops in recent weeks. The shelling so far hasn’t damaged the plant’s reactors or spent nuclear fuel storage. But it has repeatedly struck some auxiliary equipment. Fighting near the plant has fueled fears of a disaster like the one at Chernobyl, where a reactor exploded and spewed deadly radiation, contaminating a vast area in the world’s worst nuclear accident.