Improvement of LLFPs transmutation efficiency by moderator loading in lead-based fast neutron reactor.

• The long-lived fission products are one of the major impediments to the development of nuclear energy; • Long-lived fission products transmute more efficiently in thermal neutron fields compared to fast neutrons; • Metal hydrides are effective neutron moderators in reactor systems; • Transmutation efficiency of LLFPs can be effectively enhanced by appropriate moderator loading strategy in Pb-based fast reactors. The long-lived fission products (LLFPs) are one of the major impediments to the development of nuclear energy due to their longevity and toxicity. The fast neutron reactor, with its high neutron flux and excessed neutron, is a strong candidate for transmuting LLFPs. In this investigation, 79Se, 99Tc and 129I were selected as the representative nuclide of LLFPs, and then neutron moderators were loaded into the LLFPs assembly with LLFPs to evaluate the effect of different loading approaches on transmutation efficiency by the transmutation performance of LLFPs. The results show that the optimal loading strategy of moderator could increase the TR and SR with 2.35 (1.01) and 284.80 (151.11), 0.36 (0.28) and 8.06 (7.88), 1.69 (0.69) and 11.45 (7.80), respectively. It is suggested that it can transmute an additional 4500 g, 1000 g and 6600 g of these three LLFPs per year. [ABSTRACT FROM AUTHOR]