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Doppler Broadening Effect Question


I'm just learning about the Doppler feedback effect in U-238 as a result of fuel temperature (first year nuke student). I understand that as fuel temperature increases, the probability of capture in the non-fissile U-238 increases, therefor creating a negativite reactivity feedback effect. However, why doesn't this same effect happen in the resonance regions of fissile U-235, increasing the likelihood of capture and therefor fission? Or does this effect happen in U-235 but just to a lesser extent than U-238?

It doesnt have doppler broadening to any real extent. Nor is it in the core in sufficient quantity.
U235 is not a resonant absorber


Thermal Neutrons have about 0.025 electron volts worth of kinetic energy.


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