hello,everybody .Doppler coefficient will be positive?
Is this what you are asking about:
Whether the Doppler coefficient (for resonance absorption) is positive or negative depends on the composition of the fuel/core.
If resonance absorption leads to more (n,γ) and less fission then it has a negative effect on reactivity in a critical system.
If the absorption leads to more fission and less (n,γ), then it has a positive effect.
In an LWR (water moderated reactor) the Doppler coefficient is negative. The U-238 resonances absorb neutrons more readily, and to some extent, the resonance absorption of U-235 and Pu-239 resulting in (n,γ) compete with those resulting in fission.
Some fast and intermediate spectrum reactors may have a positive Doppler coefficient with certain configurations. Such configurations are to be avoided.
thank you very much
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