Uncertainty quantification of light-water-moderated and light-water-reflected cores with highly-enriched uranium fuel at Kyoto University Critical Assembly

A series of uncertainty quantifications are successfully conducted by the eigenvalue calculations, the uncertainty of criticality and reactivity, and the reduction of uncertainty using the KENO-VI code, the TSUNAMI-3D, the TSAR and the TSURFER modules of the SCALE code system, respectively. The eigenvalue calculations with KENO-VI provide noteworthy the discrepancy between experimental and numerical results of effective multiplication factor (k_eff), and the neutron spectrum dependence of k_eff in the light-water-moderated and light-water-reflected cores (C-cores) at the Kyoto University Critical Assembly (KUCA). In terms of TSUNAMI-3D, the discrepancy of k_eff is determined mainly by the uncertainty of uranium-235 (²³⁵U) fission spectrum (χ value) induced by the cross-section data, due to the use of highly-enriched uranium fuel in the KUCA C-cores. Also, the neutron spectrum dependence of k_eff is adequately understood from the effects of the uncertainty of hydrogen-1 capture, oxygen-16 elastic scattering, and aluminum-27 elastic and inelastic scattering reactions, in addition to the uncertainty of ²³⁵U fission spectrum. The reduction in the uncertainty of criticality and reactivity is interestingly achieved by the cross-section adjustment method provided in the TSURFER module, demonstrating the contribution of relevant nuclides and reactions of core components in the KUCA C-cores.