Method to Reduce Long-lived Fission Products by Nuclear Transmutations with Fast Spectrum Reactors

Abstract

Transmutation of long-lived fission products (LLFPs: 79Se, 93Zr, 99Tc, 107Pd, 129I, and 135Cs) into short-lived or non-radioactive nuclides by fast neutron spectrum reactors without isotope separation has been proposed as a solution to the problem of radioactive wastes disposal. Despite investigation of many methods, such transmutation remains technologically difficult. To establish an effective and efficient transmutation system, we propose a novel neutron moderator material, yttrium deuteride (YD2), to soften the neutron spectrum leaking from the reactor core. Neutron energy spectra and effective half-lives of LLFPs, transmutation rates, and support ratios were evaluated with the continuous-energy Monte Carlo code MVP-II/MVP-BURN and the JENDL–4.0 cross section library. With the YD2 moderator in the radial blanket and shield regions, effective half-lives drastically decreased from 106 to 102 years and the support ratios reached 1.0 for all six LLFPs. This successful development and implementation of a transmutation system for LLFPs without isotope separation contributes to a the ability of fast spectrum reactors to reduce radioactive waste by consuming their own LLFPs.

The Soreq Applied Research Accelerator Facility (SARAF): Overview, research programs and future plans

“…There are also long-lived fission products (LLFPs: 79 Se, 93 Zr, 99 Tc, 107 Pd, 129 I, and 135 Cs), which pose an additional nuclear waste challenge. It has been recently proposed to explore transmutation via fast neutron capture to shorter lived isotopes [182]. Further, the interplay between neutron capture and (n,2n) reactions may affect the transmutation efficiency [183].…”

“…Symbols: (n,) direct measurements from Macklin et al, [185] and Nakamura et al, [186]. Blue line: Fast reactor relative neutron spectrum (arbitrary units) [182].…”

"Advanced" isn't Always Better: Assessing the Safety, Security, and Environmental Impacts of Non-Light-Water Nuclear Reactors

“…For decades, elaborate schemes have been devised to attempt to separate such fission products and transmute them to stable isotopes, but none has been implemented. Even if ultimately successful, the cost and difficulty would be formidable (Chiba et al 2017). These fission products would also need to be geologically isolated in a deep underground repository for as long as some TRU isotopes.…”

Concept of a Fast Breeder Reactor To Transmute MA and LLFP

“…Regarding LLFP, a transmutation study has recently been conducted on 6 important nuclides ( 79 Se, 93 Zr, 99 Tc, 107 Pd, 129 I, and 135 Cs) from the viewpoint of reducing environmental influence. As a result, it was shown that the fast reactor can be used to transmute each of these 6 nuclides with a support ratio exceeding 1 using the YD2 moderator 28 . The significant reduction in the effective half-life was obtained by analysis.…”

“…Here, the support ratio (SR) was defined as the ratio of the amount of each nuclide transmuted by the fast breeder reactor to the amount of each nuclide (MA and LLFP) produced by the fast breeder reactor 28,30,31 .…”