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

Satoshi Chiba; Toshio Wakabayashi; Yoshiaki Tachi; Naoyuki Takaki; Atsunori Terashima; Shin Okumura; Tadashi Yoshida

doi:10.1038/s41598-017-14319-7

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

Sci Rep. 2017 Oct 24;7(1):13961. doi: 10.1038/s41598-017-14319-7.

Authors

Satoshi Chiba¹, Toshio Wakabayashi², Yoshiaki Tachi³, Naoyuki Takaki⁴, Atsunori Terashima⁵, Shin Okumura⁵, Tadashi Yoshida⁵

Affiliations

¹ Laboratory for Advanced Nuclear Energy, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8550, Japan. chiba.satoshi@nr.titech.ac.jp.
² Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi, 980-8577, Miyagi, Japan.
³ Oarai Research and Development Center, Japan Atomic Energy Agency, 4002, Narita-cho, Oaraimachi, Ibaraki, 311-1393, Japan.
⁴ Department of Nuclear Safety Engineering, Tokyo City University, 1-28-1 Tamazutsumi, Setagaya-ku, Tokyo, 158-8557, Japan.
⁵ Laboratory for Advanced Nuclear Energy, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8550, Japan.

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 10(6) to 10(2) 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.