![]() This action results in fewer neutrons available to cause fission and reduces the reactor's power output. When a control rod is inserted deeper into the reactor, it absorbs more neutrons than the material it displaces – often the moderator. Control rods are made of neutron poisons and therefore absorb neutrons. The fastest method for adjusting levels of fission-inducing neutrons in a reactor is via movement of the control rods. Some of these methods arise naturally from the physics of radioactive decay and are simply accounted for during the reactor's operation, while others are mechanisms engineered into the reactor design for a distinct purpose. Nuclear reactors typically employ several methods of neutron control to adjust the reactor's power output. The rate of fission reactions within a reactor core can be adjusted by controlling the quantity of neutrons that are able to induce further fission events. Main articles: Nuclear reactor physics, Passive nuclear safety, Delayed neutron, Iodine pit, SCRAM, and Decay heat However, in some reactors the water for the steam turbines is boiled directly by the reactor core for example the boiling water reactor. ![]() Most reactor systems employ a cooling system that is physically separated from the water that will be boiled to produce pressurized steam for the turbines, like the pressurized water reactor. The heat is carried away from the reactor and is then used to generate steam. ![]() The fission of one kilogram of uranium-235 releases about 19 billion kilocalories, so the energy released by 1 kg of uranium-235 corresponds to that released by burning 2.7 million kg of coal.Ī nuclear reactor coolant – usually water but sometimes a gas or a liquid metal (like liquid sodium or lead) or molten salt – is circulated past the reactor core to absorb the heat that it generates. This decay heat source will remain for some time even after the reactor is shut down.Ī kilogram of uranium-235 (U-235) converted via nuclear processes releases approximately three million times more energy than a kilogram of coal burned conventionally (7.2 × 10 13 joules per kilogram of uranium-235 versus 2.4 × 10 7 joules per kilogram of coal).
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