Impact of Cross-Section Uncertainties on the Nuclear Design of Hybrid Reactors

Cross-section uncertainty covariance matrices are generated and used with sensitivity coefficients to obtain estimates for the uncertainties in design parameters of a particular class of fission-fusion hybrid reactors, the SOLASE-H design. The analysis shows that the uncertainty in the ²³³U production ratio is ∼4% and is due mostly to errors associated with the lead cross sections. Reducing the uncertainty in the Pb(n,2n'), Pb(n,3n'), and the Pb(n,nonelastic) cross sections, particularly in the energy range of 9 to 20 MeV, will significantly reduce this uncertainty. Improving the Th( n, γ) cross section in the energy range of 0.35 to 3.35 keV can lead to a 40% reduction in the uncertainty in the ²³³U-breeding ratio. It is found that more accurate evaluation of the Pb(n,nonelastic) cross section in the energy range of 0.73 to 14 MeV can reduce the uncertainty in tritium breeding from ⁶Li by ∼25%. The uncertainty of only 1% found in the tritium-breeding ratio from ⁷Li indicates that present nuclear data uncertainties are adequately small. Uncertainty in displacements per atom in Zircaloy-2 cladding due to uncertainties in the Pb(n,inelastic) cross section is small. The analysis reveals the importance of reducing uncertainties in the Th(n,fission) cross sections to minimize the uncertainty in the heating rate from nuclear reactions. It is found that uncertainties in the ⁶Li(n,α.) cross section are acceptable in calculating the various nuclear parameters of the SOLASE-H design.