Transmutation of long-lived fission products (LLFPs) utilizing electron Bremsstrahlung and compact subcritical assembly

A novel approach is proposed for neutron transmutation utilizing an electron accelerator coupled with a compact subcritical system. The transmutation converter features a spherical target surrounded by a subcritical assembly composed of a moderator and low-enriched uranium in shell plates. The transmutation of six fission products, Tc-99, I-129, Cs-135, Zr-93, Se-79, and Pd-107, was investigated using electron beams with energies of 300 MeV, 30 mA and 500 MeV, 20 mA. The MCNP6.2 analyses indicate that with an electron beam of 500 MeV, 20 mA, the transmutation half-lives are all under 10 years, with 4.19 years and 5.45 years for Tc-99 and I-129, respectively, except for Zr-93, which has the longest half-life of 35 years. These transmutation half-lives represent systems with multiplication factors of approximately 0.95, and the transmutation half-life can be further reduced by raising the multiplication factor above 0.95 provided that the system’s safety at this multiplication factor is ensured.