HCSMR fuel assembly optimization with APOLLO2 and Uranie codes

The sustainability of Light Water Reactors could be improved by increasing their ability to convert ²³⁸U into ²³⁹Pu. This can be achieved by tightening the fuel assembly lattice, what reduces the moderation ratio and hence hardens the neutronic spectrum. Considering MOX fuel in such technology would even more increase the ²³⁸U conversion due to the further neutron spectrum hardening. This might however challenge the reactivity coefficient in case of loss of coolant and voided situation. To ensure a negative void coefficient, innovative fuel assembly designs were studied. The introduction of low enriched fuel rod or fertile material was assessed. A small core configuration was considered since it increases the neutron leakages in comparison to large reactor. This was also motivated by the global growing interest for small modular reactors (SMR) and led to the investigation of the high conversion small modular reactor (HCSMR) concept. This paper focuses on the optimization methods used to improve the neutron-physic performance of the HCSMR fuel assembly. The URANIE platform developed at CEA was used to set-up design of experiment, surrogate model and genetic algorithms. Those methods enable multi-criteria and multi-objective optimizations. For neutron-physic computations the deterministic code AP0LL02 compared to the Monte-Carlo code TRIP0L1-4® was used. The results obtained demonstrate the adequacy of such optimization methods for HCSMR fuel assembly design.