Adjoint Flux Spectral Fine Structure Effects on the SPT- Sensitivity Coefficients Calculation

MOX pin-cell benchmark calculations devoted to sensitivity profiles of integral parameters to cross sections by means of Standard Perturbation Theory have been carried out, using advanced CEA cell codes and libraries. As awaited, both spatial homogenization and energy collapsing procedures induce important discrepancies on the results, the most penalizing one being the spatial homogenisation. In particular, the highest discrepancies are observed in the low resolved resonance region, where the cell presents high sensitivities to nuclear data. The most important discrepancies are obtained around the absorption resonances of the fertile isotopes since these resonances induce the strongest adjoint dips (both in terms of gradient across the zones and in terms of energy fine structure). It leads to several tens of percents discrepancy for capture cross section of heavy isotopes, and up to a factor 100 or more for elastic scattering of intermediate and light nuclei. (author)