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The Reactor Monte Carlo (RMC) code, developed by the Reactor Engineering Analysis Laboratory (REAL) at Tsinghua University, is a continuous-energy Monte Carlo transport code that has been widely applied in reactor physics analyses. In recent years, its capabilities have been further extended to fusion neutronics applications. This work summarizes recent progress in the development and validation of RMC for fusion neutronics analysis, with emphasis on model conversion, transport calculation, variance reduction, tritium breeding analysis, CAD-based modeling, and shutdown dose rate assessment.
An MCNP-to-RMC conversion tool, M2R, has been developed to support the transfer of existing fusion neutronics models into the RMC framework. Representative models, including the ITER C-model and the CFETR neutronics model, have been successfully converted and used in validation studies. Based on these models, neutron transport calculations have been performed to assess the applicability of RMC to fusion neutronics problems. For the CFETR model, global neutron flux distributions, variance reduction techniques, and Tritium Breeding Ratio calculations were investigated, with results showing good agreement with OpenMC. To further extend the application range of RMC in fusion analysis, its CAD-based transport capability has also been investigated using simple tokamak CAD models. Comparative studies with OpenMC showed consistent neutronics results, demonstrating that RMC can handle both conventional converted models and more flexible CAD-based geometries for fusion reactor analysis.
A further recent development is the establishment of a fully integrated Rigorous Two-Step (R2S) framework within RMC for shutdown dose rate calculations. By extending the existing criticality transport–depletion capability to a fixed-source transport–activation coupling framework and developing a decay-photon source generation module, RMC is able to perform neutron transport, activation calculation, decay-photon generation, and photon transport within a single code system. Verification against simplified OpenMC-based reference cases showed close agreement in nuclide inventories, decay-photon spectra, and dose rates. The framework was further applied to the ITER port plug benchmark for validation, where reliable shutdown dose rate results were obtained.
These developments show that RMC has made substantial progress as an integrated tool for fusion neutronics analysis, expanding from basic transport capability toward more comprehensive support for advanced fusion applications.
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