The Nuclear Regulatory Commission has ordered the owners of the 104 nuclear power reactors in the U.S. to take three actions to improve their ability to withstand earthquakes or tsunamis. The recommendations grew from an NRC staff investigation of U.S. power plants, which was triggered by last year’s disaster at Japan’s Fukushima Daiichi nuclear power plant. An earthquake and tsunami led to a core meltdown at several Japanese reactors and a reexamination of nuclear power’s role in that country. NRC is directing U.S. plants to install better safety equipment, particularly at multireactor facilities, and improved devices to monitor water levels in spent-fuel pools. It is also ordering 23 older facilities with reactor designs identical to those at Fukushima to install systems to vent hydrogen from containment structures. The plant owners have until Dec. 31, 2016, to complete modifications. NRC also announced it intends to gather detailed new information from power plant owners. These data will include an analysis of earthquake and flooding risks as well as each plant’s ability to avoid such hazards and to operate with on-site and off-site damage without using alternating current.