United States Nuclear Regulatory Commission - Protecting People and the Environment

Containment Venting System

Improved Fukushima-Style Designs

Containment Venting System icon, consisting of a solid round, magenta cirle, with a white outline of a domed nuclear reactor building with a magenta square in the center representing a reactor and a connected vent stack with a magenta dotted line arrow going up the vent stackThe Fukushima accident disabled the plant's reactor core cooling systems, causing heat and pressure to build within the concrete and steel containment buildings that surround the reactors. This buildup eventually damaged the buildings and made it easier for radioactive material to spread to the environment. The NRC required all U.S. nuclear power plants similar in design to the Fukushima plants to improve or install a reliable, hardened vent to remove heat and pressure before potential reactor core damage. This helps preserve the integrity of the containment building, while delaying reactor core damage or melting.

Subsequently, the NRC updated the order to ensure those vents would function in the conditions following reactor core damage. Upgrades have been completed at all affected plants and verified by NRC inspectors. These upgrades were not necessary for other designs of nuclear power plants, so the order did not apply to them.

Image of Containment Venting Phase 1 system that highlights: vent, vent pipe, venting valve, suppression pool, concrete basemat, relief valve, isolation valves, reactor vessel, reactor core and steel containment ant this is not to scale image.

Page Last Reviewed/Updated Friday, January 04, 2019