Ī nuclear and radiation accident is defined by the International Atomic Energy Agency (IAEA) as 'an event that has led to significant consequences to people, the environment or the facility. Safety-critical systems were found to be undamaged by the earthquake. The Kashiwazaki-Kariwa Nuclear Power Plant, a Japanese nuclear plant with seven units, the largest single nuclear power station in the world, was completely shut down for 21 months following an earthquake in 2007.