Preliminary verification of multi-group cross-sections generation and locally heterogeneous transport calculation using OpenMC with CEFR start-up tests benchmark

Abstract

The multi-group (MG) Monte-Carlo (MC) scheme is a hybrid method based on MC solvers and deterministic strategies. This paper focuses on the study of MG schemes for the analysis of fast reactors. The MG scheme in this paper is composed of two steps. In the cross-section generation step, the OpenMC continuous-energy (CE) mode is used with 2D or 3D high-fidelity cluster geometry. In the core calculation step, both homogeneous and locally heterogeneous core models are computed using OpenMC in multi-group mode. The MG schemes are applied and validated in the China Experimental Fast Reactor (CEFR) start-up tests and compared to the CE scheme. The results show an overprediction of core criticality. The locally heterogeneous scheme improves significantly the accuracy in predicting control rod worth. Moreover, synthesizing the results from deterministic code, the locally heterogeneous scheme exhibits a stable performance across different codes, core sizes, and control rod designs. The locally heterogeneous core model with cross-sections generated from the 3D cluster has a good ability in the prediction of feedback coefficients including the sodium void reactivity, temperature reactivity, and subassembly swap reactivity. The computation speed of the locally heterogeneous MG scheme is almost the same as the homogenous MG scheme and its core calculation uses only 7.2% computation time of the reference CE scheme.