Applicability analysis of the ESSM and Tone's method in the resonance calculation of molten salt reactors

Abstract

BackgroundWith the improvement of the computer computing power, it has become a feasible scheme to generate few-group constants by two-dimensional full-core transport calculations for molten salt reactors (MSRs).PurposeThis study aims to implement resonance calculation approaches which are suitable for MSRs with complex fuel assignments or temperature distributions due to the fuel fluidity.MethodsThe general slowing-down equations of a single resonant nuclide for the subgroup, the embedded self-shielding method (ESSM), Tone's and Tone-N methods were summarized, and an integrated calculation process was designed and implemented in the ThorLAT code. The Tone-N method without uniform cross-section assumption in the Tone's method was specially proposed, and it took the influence of other fuel regions into consideration by introducing two additional fixed source equations. With the use of the SHEM361 energy group structure, the virtual environment for reactor applications (VERA) benchmark problems were used for verification and the fuel lattice of a channel-type MSR was calculated and analyzed.ResultsThe keff and pin power distributions for VERA benchmark problems are in good agreement with the reference solutions, and the maximum keff error of 2.23×10-3 is from the VERA-4B-2D case, which shows the correctness of the implementation. The results obtained with the ESSM and Tone's method, which are based on the interpolation of resonance integral tables for uniform materials, are acceptable for the MSR fuel lattice with uniform temperature or radial temperature distributions. The keff errors calculated by the ESSM and Tone's method for the MSR fuel lattice are less than 1.50×10-3, and the maximum errors of U-238 homogenized absorption cross sections in the fuel region are less than 3.1%.ConclusionsThe ESSM and Tone's method are more accurate and has a significant efficiency advantage than the subgroup method with uncorrelated model or full correlation model for the case with radial temperature distribution. The results of the Tone-N method are basically the same as those of the Tone's method, which shows that the uniform cross-section assumption in the Tone's method is reasonable. Compared with the results calculated with the XMAS172 group structure, the results obtained with the SHEM361 group structure can provide more fine spectrum structure for resolved resonances at low energy region, which can effectively improve accuracy.

Keywords

• molten salt reactors
• resonance calculation
• essm
• tone
• subgroup