"On March 11, 2011, a 9.0-magnitude earthquake, followed by a 45-foot tsunami, heavily damaged the nuclear power reactors at Japan's Fukushima Dai-ichi facility. Following this accident, the NRC [Nuclear Regulatory Commission] required significant enhancements to U.S. commercial nuclear power plants. The enhancements included: adding capabilities to maintain key plant safety functions following a large-scale natural disaster; updating evaluations on the potential impact from seismic and flooding events; new equipment to better handle potential reactor core damage events; and strengthening emergency preparedness capabilities. Combined, these actions ensure that the nuclear industry and the NRC are prepared for the unexpected."
U.S. Nuclear Regulatory Commission: https://www.nrc.gov/