Impact of residual nuclides on the transmutation of Np and Am in a lead-cooled fast reactor

Partitioning and Transmutation (P&T) is recognized as an effective strategy for mitigating the burden associated with the geological disposal of minor actinide (MA) nuclides. This study investigates the impact of three types of residual nuclides, namely, rare earth elements (REs), uranium, and plutonium, that remain in MA fuels during the partitioning process. Based on a 500 MW th lead-cooled fast reactor (LFR) developed using OpenMC, the effects of these residuals on the transmutation performance of 237 Np, 241 Am and 243 Am are systematically analyzed. The results reveal that the effective delayed neutron fraction varies non-monotonically within the 0-50 wt.% residual nuclide content range, and no significant decrease is observed. Spectral analysis demonstrates that RE 2 O 3 (rare earth oxide) and UO 2 induce spectrum softening, whereas PuO 2 hardens the spectrum. Transmutation calculations further show that for all three MAs, both the transmutation rates and capture-to-fission ratios increase approximately linearly with an increasing RE 2 O 3 and UO 2 content, whereas they decrease with an increase in PuO 2 content. This research elucidates the distinct mechanisms of these residuals in LFRs, providing a foundational basis for developing transmutation strategies for impure MA fuels.