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ImPACT under RIKEN Nishina Center

The ImPACT Program Since 2007, the Radioactive Isotope Beam Factory (RIBF) [1] has been one of the world-leading heavyion accelerator facilities for lowenergy nuclear physics. RIBF has contributed to the expansion of the nuclear chart by producing more than 140 new isotopes that have given multitudes of opportunities to discover new phenomena originating from high isospin asymmetry. In parallel to pure nuclear physics activities, a new and national program was launched for social benefits in 2014. The program, entitled “Reduction and Resource Recycling of High-Level Radioactive Wastes through Nuclear Transmutation” [2], was carried out as one of the “ImPACT” research and development (R&D) programs conducted by the Cabinet in Japan. The incident of the Fukushima Dai-ichi Unit in 2011 gave a trigger to Japanese nuclear physicists to consider possible contributions to nuclear engineering. In 2014, a demonstration experiment was performed with RIBF, where the inverse kinematics with energetic radioactive-isotope (RI) beams of 137Cs and 90Sr was employed to study spallation reaction in considering an efficient reaction pathway for reduction of the radioactivity [3]. The experiment showed future potentials of RI beams that are helpful to obtain fundamental reaction data for designing an accelerator-based transmutation system. High-level radioactive waste has two main components: long-lived fission product (LLFP) and minor actinide (MA). The transmutation of MA has been studied in detail for the purpose of reprocessing spent nuclear fuel in a concept of using fast-breeder reactors or accelerator-driven systems. On the other hand, the transmutation of LLPF has not been studied extensively. However, the LLFP nuclides are supposed to create risks in the geological disposal strategy because half-lives of LLFPs are much longer than those of MAs. By considering the present situation of R&D activities for radioactive waste, the ImPACT program was proposed by nuclear physicists and engineers together, to focus on accelerator-based transmutation for LLFPs. The ImPACT program put an emphasis on “resource recycle” of the radioactive waste. Thus, 107Pd and 93Zr were highly prioritized as objectives. The program was formed by five projects: (1) development of separation and recovery technologies, (2) obtained nuclear reaction data and new nuclear reaction control method, (3) reaction theory modeling and simulation, (4) evaluation of nuclear transmutation system and development of elemental technologies, and (5) process concept for design. All the projects were managed coherently and projects (2) and (4) were conducted by the RIKEN Nishina Center.