The spectre of an incident at the Zaporizhzhia nuclear power plant has once again reared its head, as Russia stands accused of placing "explosive devices" on the roof. So why are tensions over the nuclear facility escalating again? And if an explosion occurred at one or more of the reactors, how dangerous would it be? Sky News spoke to a nuclear expert to investigate what is happening at Europe's biggest nuclear power plant and what the level of risk is. Kremlin denies China warned Putin – Ukraine war latest updates What is the Zaporizhzhia plant and what has happened to…