Sensitivity calculations for UACSA benchmark phase III by IRSN - 5-15

The sensitivities of k_eff eigenvalue to neutron cross sections are commonly used in similarity study and as part of the validation algorithm for criticality safety assessment. To test calculation of the sensitivity coefficients, a benchmark (Phase III) has been established by OECD-NEA/WPNCS/ EG UACSA (Expert Group on Uncertainty Analysis for Criticality Safety Assessment). This paper presents some sensitivity results generated with the computational tools available or developed at IRSN. The adjoint-based first-order-linear perturbation theory sensitivity coefficients are calculated using the well know SCALE/TSUNAMI-3D Monte Carlo code, SCALE/TSUNAMI-1D deterministic code and a new module of DRAGON4 called SENS. The coupling between the APOLLO2 deterministic code and the MORET 5 multigroup Monte Carlo code generates sensitivities through direct perturbation technique. This study demonstrates the performance of the mentioned tools. The results obtained allow concluding on how model simplifications impact the sensitivity results. It also demonstrates the importance of implicit (self-shielding) sensitivities. This work also has been a useful step towards verification of the new DRAGON4/SENS and APOLLO2-MORET 5 sensitivity analysis sequences. (authors)