This animation explains the process by which a pressurized water reactor, such as those at the Oi nuclear power plant, are moderated and shutdown.

The Kansai Electric Power Co. began the shutdown process on its No. 3 reactor at the Oi nucelar power plant, in Japan's Fukui prefecture, on Monday. The shutdown will be complete by Tuesday morning, Japan time, and is required by government regulators in order to conduct scheduled safety inspections once every 13 months.