Speaker
Description
Reduction in the quantity of high-level radioactive waste in the spent fuel is one of the major issues for the use of a nuclear power plant. In recent years, substantial research and development activity has been devoted to the partitioning and transmutation technology for the reduction and recycling of radioactive waste. The transmutation on the long-lived fission products (LLFPs) in the spent fuel has attracted much attention because the LLFP nuclei have large radiotoxicities and long lifetimes, and they can be produced continuously even in the accelerator driven systems and next-generation nuclear reactors. It is essential to find effective reactions for the LLFP transmutation. However, experimental reaction data are currently lacking.
Aiming at bringing an invention to the nuclear transmutation on LLFP, we have performed systematics studies on the proton- and deuteron-induced spallation reactions for the long-lived fission products ($^{137}$Cs, $^{90}$Sr, $^{107}$Pd, $^{93}$Zr, $^{126}$Sn and $^{79}$Se) at the RIKEN RI beam factory. To overcome the difficulty in handling LLFP targets, we introduce the inverse kinematics technique. Namely, the LLFP nuclides are made as beams by in-flight fission of a $^{238}$U primary beam at 345 MeV/nucleon in the BigRIPS separator. The beams of LLFP nuclei impinge on hydrogen and deuteron targets. The reaction residues are analyzed by the ZeroDegree spectrometer. Both the LLFP beams and reaction residues are unambiguously identified event-by-event.
The present work focuses on $^{107}$Pd, which is a typical LLFP nuclide with a half-life of 6.5 $\times$ 10$^6$ years. Cross sections on both proton and deuteron were successfully obtained. To find out the optimal energy for nuclear transmutation, cross sections were obtained at different incident energies ranging from 50 to 200 MeV/nucleon. The new data were compared with theoretical calculations with intra-nuclear cascade and evaporation processes by using the PHITS framework as well as the DEURACS including the breakup process of deuteron. In the presentation, the detailed results on the LLFP nuclide $^{107}$Pd as well as the potential of spallation reaction on the LLFP transmutation will be discussed.
This work was supported and funded by ImPACT Program of Council for Science, Technology and Innovation (Cabinet Office, Government of Japan).