More than a dozen explosions rattled Europe's largest nuclear power plant over the weekend, as renewed shelling around the Ukrainian facility rekindled fears of a possible accident — or even a deliberate strike — that could cause a catastrophic release of radiation. The shelling around Ukraine's sprawling, Russian-occupied Zaporizhzhia Nuclear Power Plant came as the head of the United Nations' nuclear watchdog, the International Atomic Energy Agency (IAEA), warned in a "60 Minutes" interview that "urgent action" was needed to ease the "unprecedented" security threat posed by fighting around the facility. In an exclusive interview, one of the workers held...