Doppler Effect
Negative reactivity feedback from fuel temperature rise broadening resonance absorption peaks.
Resonance peaks in U-238 shift with thermal Doppler broadening, increasing parasitic capture at higher T. Provides prompt feedback of -1 to -3 pcm/K in LWR fuel. Essential for inherent safety, acting within ms of power surge.
Why it matters now
Doppler effect underpins passive safety in Gen III+ and SMRs, critical for 2025 NRC approvals amid HALEU-fueled microreactor pilots.