Since transmutation of LLFPs is a particle consuming process, high particle flux or intensity is, in principle, needed. Nuclear transmutation relies mainly on either neutron capture reactions or photonuclear reactions 7, 8, 9, 10. To address this problem, transmutation of LLFPs into stable or short-lived isotopes has been suggested, which should follow the principle of “as low as reasonably achievable (ALARA)” 5, 6. While the TRUs inventory can be reduced significantly by recycling and incinerating them in advanced reactors, these LLFPs will likely dominate the long-term dose associated with radionuclide release from the geologic repository, owing to their high solubility in underground water and high activeness to move to the geosphere. After recovering U and Pu from SNF by PUREX process, most of the radioactive hazards leaving in high-level nuclear wastes are radiotoxic transuranics (TRUs) or long-lived fission products (LLFPs 79Se, 93Zr, 99Tc, 107Pd, 129I, 135Cs, and 137Cs) 2, 3, 4. However, management of spent nuclear fuel (SNF) is becoming a major concern. Due to the low carbon release, nuclear energy plays an important role in facing the climate change. Nuclear energy provides almost 10% of electricity production in the world 1. It is suggested that this successful implementation of the ANES paves the avenue towards practical transmutation of LLFPs without isotopic separation. Their effective half-lives thus decrease drastically from ~ 10 6 to less than 10 2 years. 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%. 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. We investigate the effect of the ANES system layout on transmutation efficiency by Monte Carlo simulations. The PNS is produced by bombarding radioactive cesium and iodine target with a laser-Compton scattering (LCS) γ-ray beam. 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. In this study, we propose a novel concept of advanced nuclear energy system (ANES) for transmuting LLFPs efficiently without isotopic separation. 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. Disposal of long-lived fission products (LLFPs) produced in reactors has been paid a lot attention for sustainable and clean nuclear energy.
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