Research on calculation method for control rod effects in GCMR

As a novel reactor concept, the Gas-Cooled Micro-Reactor (GCMR) offers the advantages of compactness, safety, and high efficiency. However, once control rods are inserted, its complex geometry, heterogeneous material distribution, strong absorption, and significant neutron leakage result in considerable deviations when using traditional core calculation methods. To address this issue, this study investigates the control rod effects in GCMR and proposes a spline interpolation method based on neutron diffusion theory and equivalent homogenization theory. Specifically, the Monte Carlo code is performed for several representative control rod insertion ratios of the full-core calculation, from which homogenized few-group cross section of assemblies are obtained. Subsequently, a core diffusion code is employed to conduct SPH and boundary constant iterations, thereby correcting the few-group cross section and boundary constant. Finally, a spline interpolation method is applied to the few-group cross section and boundary constant corresponding to the representative control rod insertion ratios, enabling the determination of these parameters for arbitrary insertion conditions. The corrected data are then used in the diffusion code for full-core calculations. Numerical results demonstrate that the proposed spline interpolation method shows good agreement with one-step Monte Carlo results while achieving higher computational efficiency, thus providing a practical tool for fast simulation, analysis, and online monitoring of GCMR.