Simulation of JHR reactor core based on Monte-Carlo cross-section and unstructured grid method

Background The Jules Horowitz irradiation reactor (JHR) core is a 100 MW high-flux material testing reactor under construction in southern France to support existing reactor operations, life extension, and future reactor designs. However, the complex geometry of advanced reactor cores poses significant challenges for traditional deterministic methods based on structured grids.

Purpose In this paper, we explore and develop an unstructured grid method for simulating advanced cores, using simplified two-dimensional JHR cores without control rods as the model.

Methods Unstructured triangular meshes were generated using the Gmsh program with varying mesh densities. The Serpent Monte Carlo code was employed to generate six-group homogenized cross sections. Steady-state neutron diffusion calculations were performed using VITAS, a general-purpose neutron diffusion solver developed by Shanghai Jiao Tong University.

Results The effective multiplication factor (k_eff) calculated by VITAS converged with increasing mesh refinement, achieving agreement within 4×10⁻³ of the Monte Carlo reference value of 1.35958. The maximum relative deviation in assembly power distribution was within 3%, occurring at the peripheral fuel positions. The multi-group flux distributions showed good consistency between the two codes, with a maximum relative deviation of 8.6%.

Conclusions The proposed unstructured grid method demonstrates satisfactory accuracy for steady-state analysis of complex reactor cores. This approach offers valuable reference for modeling other advanced reactors with intricate geometries where structured grids are inadequate.