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
Flooding (nuclear reactor core) (or other) flow regime. The significance of this phenomenon is that, if not properly designed for, it can present issues when trying to fill the core with liquid (the phenomenon works against gravity, forcing liquid out of the core). In a boiling water reactor (BWR), the emergency core cooling system (ECCS) injects liquid water into the reactor core from the top. Water vapor produced from boiling will flow in the opposite direction. Given a high enough flow rate of steam, reversal of the ECCS-injected liquid water occurs. In a pressurized water reactor (PWR), the ECCS injects liquid into the hot