Fuel temperature coefficient of reactivity

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.

See also

References

  1. ↑ Friant, David; Bernard, David; Blaise, Patrick (2023-08-03). "State of the Art on Doppler Broadening: Modern Developments on the Fuel Temperature Coefficient". Nuclear Science and Engineering. 197 (8): 1991–2006. doi:10.1080/00295639.2022.2158679. ISSN 0029-5639. Retrieved 2026-08-25.
  2. ↑ "Self-shielding". Nuclear Power. Retrieved 25 August 2026.
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