Sensitivity of the neutron multiplication factor to gadolinium isotopes' nuclear data for light water reactor fuel assemblies in the peak reactivity burnup range

Highlights: • Sensitivities of peak reactivity of LWR fuel assemblies are quantified. • Usefulness of the depletion perturbation theory-based capability is demonstrated. • Peak reactivity uncertainty induced by Gd (n,g) cross section is generally small. • Gd-155 nuclear data uncertainty is rather important than Gd-157 nuclear data uncertainty. The reactivity of a fuel assembly including burnable absorbers can become the largest at low fuel burnup, so the accuracy of reactivity calculations for such systems is important. To investigate this issue, the impact of gadolinium isotopes' nuclear data on neutron multiplication factor k is quantified. Sensitivities of k to nuclear data are calculated from 0 to 20 GWD/t for a BWR 3 × 3 multicell model. Sensitivity to gadolinium-157 (n,$\gamma$) cross section becomes the largest at the zero burnup. Sensitivity to gadolinium-155 (n,$\gamma$) cross sections takes the two largest values and the second one is observed around fuel burnup where the reactivity reaches its peak. Sensitivities are also calculated for BWR and PWR assemblies, and similar trends are observed. Finally, nuclear data-induced uncertainties of k are quantified. Gadolinium-157 contribution is the largest at zero burnup, and gadolinium-155 contribution is relatively important around fuel burnup corresponding to the reactivity peak.