Fuel temperature coefficient of reactivity
Measure of nuclear reactor fuel stability
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Fuel temperature coefficient of reactivity is the change in reactivity of the nuclear fuel per degree change in the fuel temperature. It is a measure of the stability of the reactor operations (that is, its value is normally negative). This coefficient is also known as the Doppler coefficient due to the contribution of Doppler broadening, which is the dominant contribution to the effect.[1]
Contributing effects
Doppler broadening
The thermal motion of atoms within the fuel causes a broadening of the resonance peaks of the neutron capture cross-section of the non-fissile portions of the fuel (notably, uranium-238). Since the resonances are self-shielding, their broadening results in an overall reduction of neutron flux as the temperature increases.[2]
Thermal expansion
Thermal expansion of the fuel at higher temperatures results in a lower density which reduces the likelihood of a neutron interacting with the fuel.
