Study on the relation between Doppler reactivity coefficient and resonance integrals of Thorium and Uranium in PWR fuels

• We used sensitivity coefficient to decompose Doppler reactivity coefficient.
• Relative change of capture cross-section of Th-232 is larger than that of U-238.
• Narrower resonance is more sensitive to Doppler Effect than wider one.
• Resonance width has a large impact on Doppler reactivity coefficient.

Doppler reactivity coefficient of Thorium fuel is negatively larger than that of Uranium fuel, although resonance integral of Th-232 is smaller than that of U-238.The purpose of this study is to reveal the mechanism of the opposite tendency of Doppler reactivity coefficient and resonance integral between Thorium fuel and Uranium fuel.Larger Doppler reactivity coefficient is caused by larger relative change of capture cross-section of Th-232, and the larger change results from narrower resonance width. In addition, narrower resonance width causes smaller resonance integral.It was found that resonance width is the key parameter to understand the opposite tendency of Doppler reactivity coefficient and resonance integral between Thorium fuels and Uranium fuels.