An attack on the nuclear material at a power plant could release cancer causing radioactivity at least within Ukraine, experts said Friday. Some of the scenarios that might occur during an attack on a nuclear plant include a direct hit, such as a missile strike, that damages the reactor; a strike on a pool where spent nuclear fuel is cooling; or an attack that disrupts the electrical supply to the plant and affects the systems that keep the nuclear core of a reactor cool. “There’s a number of ways this can go very bad,” Allison Macfarlane, a former chairman of the US Nuclear Regulatory Commission, said.