Pursuant to Canada’s small modular reactor (SMR) action plan to achieve net-zero emissions, a SMR based on gas-cooled reactors (GCRs) is one of the potential concepts among the non-water-cooled reactor technologies to be considered for deployment in the near future in Canada. A coupled modeling approach to account for feedback effects using higher-fidelity solutions is becoming increasingly viable due to improvements in phenomenological models and advanced computing. This study aims to improve simulation accuracy for the prismatic block GCR scenarios of interest using an integrated coupled modeling toolset that loosely couples computational fluid dynamics (CFD), system thermalhydraulics (TH), and neutronics codes.

The differentiating aspect of this study is the execution of three-way coupled analyses for the GCRs that can account for both the component- and system-level scales. Within this study, a part of the reactor core was simulated using CFD, coupled with a one-dimensional system TH code for the solution of the rest of the reactor circuit. The power feedback effects inside the reactor core simulated with CFD were obtained from a neutronics solver. An explicit representation of the core components was undertaken in the CFD model to facilitate the detailed modeling of the coolant flow within the channels and its interaction with the reflectors, fuel, and control rods.

Two industrially relevant test operating scenarios, fully withdrawn and incremental increase of insertion level of control rods, were simulated to showcase the suitability of the coupled analyses. The reactivity coefficients and control rod worth using the coupled multiphysics analyses are presented. The results demonstrate the capability of the developed algorithm for coupling three modeling disciplines for its application in GCR core simulations.