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
MIT Nuclear Research Reactor boron-stainless steel blade-type control rods and one aluminum with cadmium control rod which can be placed on automatic control. Light water flows upwards through the core and a tank of heavy water surrounds the core. A wall of dense concrete that serves as shielding surrounds the tank of heavy water. The maximum coolant temperature is 55 degrees Celsius. The light water and heavy water are cooled using forced circulation through heat exchangers to a secondary coolant system. The heat from the reactor is ultimately dissipated to the atmosphere via the secondary cooling system using two modular Tower Tech cooling towers