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NaK was used as the coolant in the first breeder reactor prototype, the Experimental Breeder Reactor-1, in 1951. Sodium and NaK do, however, ignite spontaneously on contact with air and react violently with water, producing hydrogen gas. This was the case at the Monju Nuclear Power Plant in a 1995 accident and fire. Sodium is also the coolant ...
NaK containing 40% to 90% potassium by mass is liquid at room temperature.The eutectic mixture consists of 77% potassium and 23% sodium by mass (NaK-77), and it is a liquid from −12.6 to 785 °C (9.3 to 1,445.0 °F), and has a density of 0.866 g/cm 3 at 21 °C (70 °F) and 0.855 g/cm 3 at 100 °C (212 °F), making it less dense than water. [3]
A nuclear reactor coolant is a coolant in a nuclear reactor used to remove heat from the nuclear reactor core and transfer it to electrical generators and the environment. Frequently, a chain of two coolant loops are used because the primary coolant loop takes on short-term radioactivity from the reactor.
The effects of a nuclear meltdown depend on the safety features designed into a reactor. A modern reactor is designed both to make a meltdown unlikely, and to contain one should it occur. In a modern reactor, a nuclear meltdown, whether partial or total, should be contained inside the reactor's containment structure.
In most reactor plant designs, however, this would not limit flowrate through the core and therefore would behave like a loss-of-pressure-control-accident rather than a loss-of-coolant accident. Failure of either the spray nozzles (failing open would inhibit raising pressure as the relatively cool spray collapses the pressurizer vessel bubble ...
On the other hand, if a reactor is designed to operate with no voids at all, a large negative void coefficient may serve as a safety system. A loss of coolant in such a reactor decreases the thermal output, but of course heat that is generated is no longer removed, so the temperature could rise (if all other safety systems simultaneously failed).
The Fukushima Daiichi nuclear disaster in 2011 occurred due to a loss-of-coolant accident. The circuits that provided electrical power to the coolant pumps failed causing a loss-of-core-cooling that was critical for the removal of residual decay heat which is produced even after active reactors are shut down and nuclear fission has ceased.
Most nuclear power plants feature a containment building whose role is to be the ultimate barrier, as per the defense-in-depth principle, against the release of radionuclides in the environment during accidents involving partial or total reactor core damage, that is, in which the integrity of the nuclear fuel (first barrier) is lost.