Fuel temperature coefficient of reactivity is the change in reactivity of the nuclear fuel per degree change in the fuel temperature. The coefficient quantifies the amount of neutrons that the nuclear fuel (such as
uranium-238
Uranium-238 (238U or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However ...
) absorbs from the
fission
Fission, a splitting of something into two or more parts, may refer to:
* Fission (biology), the division of a single entity into two or more parts and the regeneration of those parts into separate entities resembling the original
* Nuclear fissio ...
process as the fuel temperature increases. It is a measure of the stability of the
reactor operations. This coefficient is also known as the Doppler coefficient due to the contribution of
Doppler broadening
In atomic physics, Doppler broadening is broadening of spectral lines due to the Doppler effect caused by a distribution of velocities of atoms or molecules. Different velocities of the emitting (or absorbing) particles result in different Dopp ...
, which is the dominant effect in thermal systems.
Contributing effects
Doppler broadening
Thermal Doppler motion of atoms within the fuel results in a broader neutron spectrum and, consequently, in a decreased neutron capture rate.
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
*
Nuclear fission
Nuclear fission is a nuclear reaction, reaction in which the atomic nucleus, nucleus of an atom splits into two or more smaller atomic nucleus, nuclei. The fission process often produces gamma ray, gamma photons, and releases a very large ...
*
Nuclear reactor physics
*
Void coefficient
In nuclear engineering, the void coefficient (more properly called void coefficient of reactivity) is a number that can be used to estimate how much the reactivity of a nuclear reactor changes as voids (typically steam bubbles) form in the reactor ...
References
USNRC Glossary
Nuclear technology
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