Research and Preliminary Verification of the Resonance Self-Shielding Calculation Method for the High-Fidelity Neutronics Code VITAS

Abstract VITAS is a high-fidelity neutronics code developed by Shanghai Jiao Tong University based on the heterogenous variational nodal method (HVNM). In previous publications, VITAS has been successfully verified for transport calculations against macroscopic benchmarks. However, advancing the research on the resonance self-shielding calculation method within VITAS remains crucial for efficient one-step neutronics calculations. This paper presents the implementation of the subgroup method in VITAS. Subgroup parameters are obtained through least squares fitting based on the resonance cross-sections table. The narrow resonance approximation elastic scattering model is employed for the scattering source term, and a subgroup transport equation is established. The subgroup transport equation is solved using the HVNM, yielding subgroup fluxes. Effective resonance self-shielding cross-sections are obtained using the subgroup fluxes to weight the subgroup cross-sections. Additionally, the Bondarenko method is applied to address multiple resonance nuclide interference effects. This paper conducts preliminary verification of resonance self-shielding calculation method through a series of benchmark problems. The numerical results suggest that the effective resonance self-shielding cross-sections and eigenvalue obtained from VITAS show good agreements with the reference solutions provided by Monte Carlo code OpenMC. This consistency demonstrates the capability of VITAS in addressing heterogeneous resonance self-shielding problems.