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Control rods are used in nuclear reactors to control the rate of fission of the nuclear fuel – uranium or plutonium. Their compositions include chemical elements such as boron , cadmium , silver , hafnium , or indium , that are capable of absorbing many neutrons without themselves decaying.
In light-water reactors, this is achieved by inserting neutron-absorbing control rods into the core, although the mechanism by which rods are inserted depends on the type of reactor. In pressurized water reactors the control rods are held above a reactor's core by electric motors against both their own weight and a powerful spring. A scram is ...
Control rods are a series of rods that can be quickly inserted into the reactor core to absorb neutrons and rapidly terminate the nuclear reaction. [2] They are typically composed of actinides, lanthanides, transition metals, and boron, [3] in various alloys with structural backing such as steel. In addition to being neutron absorbent, the ...
A control rod is removed from or inserted into the central core of a nuclear reactor in order to control the number of neutrons which will split further uranium atoms. This in turn affects the thermal power of the reactor, the amount of steam generated, and hence the electricity produced. The control rods are partially removed from the core to ...
When the control rods are lowered into the core, they absorb neutrons, which thus cannot take part in the chain reaction. Conversely, when the control rods are lifted out of the way, more neutrons strike the fissile uranium-235 (U-235) or plutonium-239 (Pu-239) nuclei in nearby fuel rods, and the chain reaction intensifies.
Assuming that at the moment that the accident occurs the reactor will be SCRAMed (immediate and full insertion of all control rods), so reducing the thermal power input and further delaying the boiling. The time required for the fuel to melt. After the water has boiled, then the time required for the fuel to reach its melting point will be ...
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Hydrogen embrittlement may also occur in the reactor materials and volatile fission products can be released from damaged fuel rods. Between 1,300 and 1,500 °C (2,370 and 2,730 °F), the silver-indium-cadmium alloy of control rods melts, together with the evaporation of control rod cladding. At 1,800 °C (3,270 °F), the cladding oxides melt ...