Transmutation of long-lived fission products in an advanced nuclear energy system

Abstract

Disposal of long-lived fission products (LLFPs) produced in reactors has been paid a lot attention for sustainable and clean nuclear energy. Although a few transmutation means have been proposed to address this issue, there are still scientific and/or engineering challenges to achieve efficient transmutation of LLFPs. In this study, we propose a novel concept of advanced nuclear energy system (ANES) for transmuting LLFPs efficiently without isotopic separation. The ANES comprises intense photoneutron source (PNS) and subcritical reactor, which consist of lead–bismuth (Pb-Bi) layer, beryllium (Be) layer, and fuel, LLFPs and shield assemblies. The PNS is produced by bombarding radioactive cesium and iodine target with a laser-Compton scattering (LCS) γ-ray beam. We investigate the effect of the ANES system layout on transmutation efficiency by Monte Carlo simulations. It is found that a proper combination of the Pb-Bi layer and the Be layer can increase the utilization efficiency of the PNS by a factor of ~ 10, which helps to decrease by almost the same factor the LCS γ-beam intensity required for driving the ANES. Supposing that the ANES operates over 20 years at a normal thermal power of 500 MWt, five LLFPs including 99Tc, 129I, 107Pd, 137Cs and 79Se could be transmuted by more than 30%. Their effective half-lives thus decrease drastically from ~ 106 to less than 102 years. It is suggested that this successful implementation of the ANES paves the avenue towards practical transmutation of LLFPs without isotopic separation.

Transmutation of MAs and LLFPs with a lead-cooled fast reactor

“…The moderator could soften the neutron at the LLFPs assembly region while having little effect on the neutron energy spectrum of the entire core, as it is loaded in the radial blanket region with a small loading mass. The isotope abundances of these LLFPs nuclides are shown in Table 4 , and their chemical forms for assembly loading are explained in detail in our previous work 23 .…”

“…If an average of approximately 1 wt% MAs is loaded to the LFR core, a transmutation rate of 10% per year or more was foreseen without deterioration of the core characteristics 6 . For LLFPs, an advanced nuclear energy system driven by an intense photoneutron source has been proposed to transmute efficiently the LLFPs assembly composed of 79 Se, 93 Zr, 99 Tc, 107 Pd, 129 I, 135 Cs and 137 Cs 23 . It is shown that the 79 Se, 99 Tc, 107 Pd, 129 I and 137 Cs could be transmuted by more than 30% within 20 years and their effective half-lives can decrease drastically from ~ 10 6 to less than 10 2 years.…”