Session: 13-01: Computer Code V&V - I

Paper Number: 133419

133419 - Research and Preliminary Verification of the Resonance Self-Shielding Calculation Method for the High-Fidelity Neutronics Code VITAS 

Abstract: 

In recent years, with the advancements in computational resources, the one-step neutron transport method with homogenization eliminated has garnered increasing attention as a prominent research focus. The heterogenous variational nodal method has been proven to be another viable option for achieving one-step whole-core neutronics calculations, besides the method of characteristics. The heterogenous variational nodal method treats each pin cell as a single node and utilizes iso-parametric finite element to accurately represent the pin-resolved geometry. Angular expansion is achieved using spherical harmonics, while radial and axial leakage expansion employ polynomials and piece-wise constants, respectively. VITAS is a high-fidelity neutronics code developed by Shanghai Jiao Tong University based on the variational nodal method. To enhance computational efficiency, VITAS incorporates acceleration methods including the flat source acceleration method, the partitioned matrix method, and the quasi-reflective boundary condition acceleration method. It also features parallel computing capabilities based on Message Passing Interface standard and a non-overlapping domain decomposition strategy. In previous publications, VITAS has been successfully verified for transport calculations against macroscopic benchmarks, including C5G7, KAIST, and JRR-3. However, advancing the research on the resonance self-shielding calculation method within VITAS remains crucial for efficient one-step neutronics calculations. Resonance self-shielding calculation is pivotal for accurately estimating the effective resonance self-shielding cross-section of resonant nuclides in resonance energy groups, a factor that considerably influences the accuracy of transport calculations. Resonance self-shielding calculation methods are generally categorized into equivalence theory method, ultrafine group method, and subgroup method. The subgroup method, benefiting from its geometric adaptability and favorable balance between accuracy and efficiency, is widely used in high-fidelity one-step calculation codes. This paper presents the implementation of the subgroup method in VITAS based on a 69-group multi-group cross-section library to characterize the complex resonance self-shielding effects. 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 heterogenous variational nodal method, yielding subgroup fluxes. Effective resonance self-shielding cross-sections are obtained using the subgroup fluxes to weight the subgroup cross-sections. Additionally, the Bondarenko iterative 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 typical benchmarks. The numerical results suggest that the effective resonance self-shielding cross-sections and k_eff 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 resonance self-shielding problems.

Presenting Author: Han Yin Shanghai Jiao Tong University

Presenting Author Biography: Han Yin graduated with a B.S. degree in Radiation Protection and Nuclear Safety from Lanzhou University, China, in 2018, followed by an M.S. degree in Nuclear Energy and Nuclear Engineering from Shanghai Jiao Tong University, China, in 2021. He is presently pursuing his Ph.D. in Nuclear Science and Technology at the School of Nuclear Science and Engineering, Shanghai Jiao Tong University. His research primarily delves into deterministic reactor physics calculation methods. Through his work, he aspires to make a substantial contribution to the field of nuclear engineering, particularly in enhancing the accuracy and efficiency of reactor physics calculation method. He has been actively involved in several research projects and has contributed to publications in the domain of nuclear engineering.

Authors:

Han Yin Shanghai Jiao Tong University
Tengfei Zhang Shanghai Jiao Tong University
Xiaojing Liu Shanghai Jiao Tong University