In recent years, interest in (very) small and medium size reactor– (v)SMR – concepts for specific purposes has grown. They are characterized by irregular geometries. Though Monte Carlo methods for safety assessment are becoming more and more standard for steady state simulations, they are not yet mature enough for transient applications. To perform future coupled transient safety assessments of (v)SMRs, the Finite ElemeNt NEutroniCS (FENNECS) code is being developed at GRS. It solves the time-dependent and steady-state 3-d few-group diffusion equation in Galerkin finite element representation using upright triangular prisms with linear basis functions as spatial elements. FENNECS is also coupled with the GRS thermal-hydraulic system code ATHLET. For spatial meshing, FENNECS includes an internal meshing module for regular Cartesian and hexagonal lattices. It also allows to read node lists and element connectivities from external ASCII files. For the meshing of the irregular geometries of (v)SMRs, an external meshing tool is being developed as a Python software module which generates the data required by FENNECS. This paper considers the Heat Pipe Micro Reactor core proposed in the publicly available document “Multi-Physics Simulations of Heat Pipe Micro Reactor” (ANL/NSE-19/25). The specification provides a detailed description of all geometries. The core layout is composed of a hexagonal fuel pin lattice surrounded by six control rod drums. However, no mass density of any material is given and must be gathered from opened literature. Two Monte Carlo Serpent models are developed for comparing with the results presented in the benchmark and for the generation of homogenized few-groups cross-sections to be used in FENNECS. Two configurations are considered, one where the absorber face of all control drums are turned out of the core (named All Rods Out – ARO – configuration) and the other one where all absorber faces are turned in (All Rods In – ARI – configuration). The multiplication factors obtained in these two configurations are in good agreement with the benchmark. The challenge of modelling this reactor in FENNECS is to properly mesh the circular shape of control drums into a hexagonal lattice. They are approximated by a polygon, either with 12 or 24 edges, which conserves the area of the circle. The preliminary FENNECS results on the multiplication factor are in good agreements with Serpent reference results for both ARO and ARI configurations. This demonstrates the applicability of FENNECS, the features of which will be presented in this paper, to (v)SMRs.
|Affiliation/Organization||Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH|
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