Estimation of resonance self-shielding effect in PWR pin cell for different fuel types

The most important factors in any code used for nuclear reactor modeling are the time and precision of the results. In principle, deterministic codes are used in calculations due to the long computational time required by stochastic codes to achieve reliable results. The accuracy of deterministic codes is related to the method used in treating the resonance self-shielding behavior of the cross-sections; hence it is essential to select the best self-shielding method. Both the equivalence in dilution, and the subgroup approaches are used to represent the self-shielding effect in PWR pin cell. The calculations are performed using three classes of subgroup approaches based on physical and mathematical (Ribon extended model and subgroup projection method) probability tables. In the present paper, various cross-section library formats are considered to assess the performance of three PWR fuel types: UO2, PuO2-UO2, and ThO2-UO2, using DRAGON4 and WIMS-D5 codes. The accuracy of the calculations is determined by comparison with the stochastic MCNP6 code. The results obtained indicate that the radial sub-divisions and proper resonance treatment are required to treat the rim effect. This is demonstrated in DRAGON code that can accurately calculate the radial distributions for all reaction rates.