Nuclear safety and security called a nuclear meltdown. After shutting down, for some time the reactor still needs external energy to power its cooling systems. Normally this energy is provided by the power grid to which that plant is connected, or by emergency diesel generators. Failure to provide power for the cooling systems, as happened in Fukushima I, can cause serious accidents. Nuclear safety rules in the United States "do not adequately weigh the risk of a single event that would knock out electricity from the grid and from emergency generators, as a quake and tsunami recently did in Japan", Nuclear Regulatory Commission officials
Nuclear reactor accidents in the United States damage costs include destruction of property, emergency response, environmental remediation, evacuation, lost product, fines, and court claims. Because nuclear reactors are large and complex, accidents onsite tend to be relatively expensive. In the U.S., at least 56 nuclear reactor accidents have occurred. The most serious of these U.S. accidents was the Three Mile Island accident in 1979. According to the Nuclear Regulatory Commission, the Davis–Besse Nuclear Power Station has been the source of two of the top five most dangerous nuclear incidents in the United States since 1979. The United States Government Accountability Office reported more than 150 incidents from