Sensitivity of Cross Sections to Isotopic Densities for Subgroup Resonance Self-Shielding Calculations

The sensitivity coefficients of self-shielded cross sections to isotopic densities are computed for a subgroup resonance self-shielding model. The method we propose is based on the derivatives of the collision probabilities used in the slowing-down equation. In this work, we look at how the sensitivities vary as a function of the position inside a fuel pin or of the position of a fuel pin within an assembly. Moreover, we evaluate the importance of the superhomogenization factors, used to correct self-shielded cross sections for the subgroup method, on the cross-section sensitivities. We also present a comparison with the Monte Carlo code Serpent where the sensitivity coefficients are approximated using a finite difference method.