Deterministic Model of PWR Fast Fluence for Uncertainty Propagations with the Code APOLLO3^®

The fast neutron fluence and the corresponding uncertainty are important parameters for reactor pressure vessel lifetime. This article presents one model, under development at CEA (Commissariat à l’Energie Atomique et aux Energies Alternatives), that uses the deterministic code APOLLO3^® for uncertainty calculations of the fast fluence for pressurized water reactor irradiation surveillance. All calculations are made by MINARET, a 3D-SN solver of the APOLLO3^® code that uses the discontinuous Galerkin finite elements approximation. The spatial mesh is unstructured, and the transport calculations are parallelized with respect to the angular directions. In this numerical scheme, the multigroup cross sections are sub-group self-shielded and collapsed over a dedicated energy mesh optimized by the adaptive energy mesh constructor. Results from this model are encouraging with respect to the Monte Carlo reference TRIPOLI-4^®. The integral of the flux over 1 MeV in the locations of interest (surveillance capsule and vessel) is calculated in less than 20 min with an error lower than 1 %. Some examples of uncertainty calculations associated with design parameters in which the MINARET solver is coupled to the CEA uncertainty and sensitivity platform URANIE are also provided.