Nuclear Data–Induced Uncertainty of Criticality in Solid-Moderated and Solid-Reflected Cores with Highly Enriched Uranium Fuel at Kyoto University Critical Assembly

Nuclear data–induced uncertainty of criticality is successfully analyzed by combining the eigenvalue calculations, the uncertainty, and the reduction of uncertainty with the use of the KENO-VI code, the TSUNAMI-3D and the TSURFER modules of the SCAL6.2.4 code system, respectively. The comparative study of conventional and revised S(α, β) applications is also conducted by KENO-VI. Notably, the KENO-VI analyses reveal the difference between the experimental and numerical results of criticality and the neutron spectrum dependence of criticality on the H/U ratio in the solid-moderated and solid-reflected cores at the Kyoto University Critical Assembly (KUCA). The difference is identified as the leading cause of uncertainty in the ²³⁵U fission spectrum (χ value) through the combined use of the uncertainty and the cross-section adjustment by TSUNAMI-3D and TSURFER, respectively, especially that the highly enriched uranium (HEU) fuel is loaded into the KUCA cores. Also, the neutron spectrum dependence of criticality is attributable to the uncertainty induced by the cross-section data of ²³⁵U capture, ²⁷Al elastic scattering, and inelastic scattering reactions in the HEU fuel plate and to the ¹H capture reactions in the polyethylene moderator through the TSUNAMI-3D analyses.