Development and verification of neutron-photon coupling calculation based on VINUS

Traditional reactor physics analysis methods often neglect the impact of photon heating when solving advanced reactor problems. Building upon neutron and photon cross-section processing, a coupled calculation methodology integrating neutron critical calculation, photon source generation, and photon fixed-source computation is more conducive to accurately analyzing the overall power distribution in advanced reactors. This study develops a neutron-photon coupled calculation module and implements it by improving the VINUS code. Validation was performed against the typical structured-mesh fast reactor benchmark RBEC-M and the experimental benchmark ZPPR-15D for power distribution from neutron-photon coupled calculations. Furthermore, validation of the unstructured mesh neutron-photon coupled calculation capability was conducted using the TOPAZ-II space reactor benchmark, which features a mixed spectrum and complex geometry. Results demonstrate that VINUS achieves good agreement with reference solutions or experimental values. The smallest errors in neutron-photon coupled power calculations occur in the fuel region, while error magnitudes in breeding/moderator zones depend on strong anisotropic scattering and significant flux gradients. The study confirms the importance of photon heating (approximately 10% of total power) and the established code system's capability for high-fidelity core physics analysis of advanced reactors with complex geometries and energy spectra.