Development of a Diffusion Core Calculation Scheme for the GCMR

As a promising solution to the challenges of future clean and reliable energy supply, the Gas-Cooled Micro-Reactor (GCMR) has attracted increasing attention due to its potential for decentralized power generation, carbon-free operation, and flexible deployment in remote or extreme environments. As a novel reactor concept, the GCMR offers advantages such as compact size, inherent safety, and high thermal efficiency. However, conventional core calculation methods face significant challenges due to the complex geometric configurations, heterogeneous material distribution, and pronounced neutron leakage characteristics of the GCMR. This study proposes a diffusion-based homogenization method for GCMR analysis. First, the Monte Carlo code RMC is employed to perform assembly-level homogenization and tally the few-group cross sections of representative assemblies. These cross sections are then corrected using the Super Homogenization (SPH) method to preserve reaction rate consistency. Subsequently, the Iterative Albedo (IA) procedure is applied to obtain accurate albedo values, thereby ensuring conservation of neutron leakage. Finally, the diffusion code, incorporating the SPH-IA method, is utilized to perform full-core GCMR analysis. Numerical results demonstrate that employing a 25-group energy structure with the SPH-IA method produces results in good agreement with reference Monte Carlo values, while maintaining high computational efficiency across a range of conditions—including varying energy group structures, temperatures, irradiation time, and control rod insertion ratios. Furthermore, a quadratic fitting function for albedo as a function of operational parameters is developed, providing a feasible and accurate approach for the core design and neutronic analysis of GCMR.