Spallation Reaction Study for Fission Products in Nuclear
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Physics Letters B 754 (2016) 104–108 Contents lists available at ScienceDirect Physics Letters B www.elsevier.com/locate/physletb Spallation reaction study for fission products in nuclear waste: 137 90 Cross section measurements for Cs and Sr on proton and deuteron ∗ H. Wang a, , H. Otsu a, H. Sakurai a, D.S. Ahn a, M. Aikawa b, P. Doornenbal a, N. Fukuda a, T. Isobe a, S. Kawakami c, S. Koyama d, T. Kubo a, S. Kubono a, G. Lorusso a, Y. Maeda c, A. Makinaga e, S. Momiyama d, K. Nakano f, M. Niikura d, Y. Shiga g,a, P.-A. Söderström a, H. Suzuki a, H. Takeda a, S. Takeuchi a, R. Taniuchi d,a, Ya. Watanabe a, Yu. Watanabe f, H. Yamasaki d, K. Yoshida a a RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan b Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan c Department of Applied Physics, University of Miyazaki, Miyazaki 889-2192, Japan d Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan e Graduate School of Medicine, Hokkaido University, North-14, West-5, Kita-ku, Sapporo 060-8648, Japan f Department of Advanced Energy Engineering Science, Kyushu University, Kasuga, Fukuoka 816-8580, Japan g Department of Physics, Rikkyo University, 3-34-1 Nishi-Ikebukuro, Toshima, Tokyo 171-8501, Japan a r t i c l e i n f o a b s t r a c t 137 90 Article history: We have studied spallation reactions for the fission products Cs and Sr for the purpose of nuclear Received 27 August 2015 waste transmutation. The spallation cross sections on the proton and deuteron were obtained in inverse Received in revised form 14 December 2015 137 90 kinematics for the first time using secondary beams of Cs and Sr at 185 MeV/nucleon at the RIKEN Accepted 29 December 2015 Radioactive Isotope Beam Factory. The target dependence has been investigated systematically, and the Available online 11 January 2016 cross-section differences between the proton and deuteron are found to be larger for lighter spallation Editor: D.F. Geesaman products. The experimental data are compared with the PHITS calculation, which includes cascade and Keywords: evaporation processes. Our results suggest that both proton- and deuteron-induced spallation reactions Spallation reaction on proton and deuteron are promising mechanisms for the transmutation of radioactive fission products. Transmutation of long-lived fission products © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license 137 3 Cs (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP . 90Sr 1. Introduction minor actinide (MA). The transmutation of MA has been studied in detail for the purpose of reprocessing spent nuclear fuel in a con- Nuclear power has provided a modern source of energy since cept of using the accelerator-driven system (ADS) [2]. For instance, the middle of the twentieth century. Because the nuclear power proton/deuteron-induced spallation reactions of heavy stable nu- stations do not produce greenhouse gases, nuclear power is con- clei have been investigated at GSI for ADS targets [3,4]. On the sidered as a potential candidate to mitigate climate change while other hand, the transmutation of LLFP has not been studied as ex- delivering a large amount of energy. However, nuclear safety and tensively because they are not considered to be useful materials for security are matters of concern to the entire world. Reduction in power production. In addition, LLFP can be produced continuously the quantity of high-level radioactive waste is one of the major is- in ADS systems and next-generation nuclear reactors, for instance sues for the use of a nuclear power plant. fast breeder reactors. Research and development into the reduction of radioactive However, the transmutation on 137Cs and 90Sr, which have large waste using partitioning and transmutation technology has been weight fractions (40%) in LLFP, has received much attention. These performed over recent decades [1]. High-level radioactive waste two isotopes have large radiotoxicities due to their relatively short has two main components: long-lived fission product (LLFP) and half lives of 30 years [5]. Indeed, their radiotoxicities are predomi- nant (more than 90%) in the first 100 years after the reprocessing * Corresponding author. of spent fuel. In addition, these two LLFP nuclei are the major 137 90 E-mail address: [email protected] (H. Wang). source of heat in high-level nuclear waste [1]. Cs and Sr have http://dx.doi.org/10.1016/j.physletb.2015.12.078 0370-2693/© 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3. H. Wang et al. / Physics Letters B 754 (2016) 104–108 105 small thermal neutron-capture cross sections [6,7] and, therefore, isotopes 137Cs and 90Sr were well separated from others in the it is essential to find other effective reactions for their transmuta- secondary beams and were clearly selected for the data analysis. tion. The possibility of proton-induced spallation reaction has been The typical intensities of the 137Cs and 90Sr beams were 1.2 × 103 discussed in Refs. [8,9]; however, experimental reaction data are and 7.1 × 103 particles per second, with purities of 14% and 28%, currently lacking. respectively. 2 2 Nuclear physics plays an essential role in addressing the treat- Three targets, 179.2-mg/cm CH2, 217.8-mg/cm CD2 [15], and ment on LLFP, because the reliable reaction data and models are 226.0-mg/cm212C, were used to induce the secondary reactions; necessary for LLFP reactions. Thanks to the radioactive isotope the thicknesses were chosen so that the energy losses of both sec- beams, the mechanisms of spallation reactions of LLFP nuclei on ondary beams were similar in each target. Therefore, data could be proton and deuteron can be investigated. Because the proton– obtained for all targets using a common setting for the ZeroDegree proton and proton–neutron interaction cross sections are known spectrometer [11]. Uncertainties of the thicknesses, determined by to be different, it is therefore important to study the cross-section weight measurement, were less than 2%. In order to obtain the differences in long-lived fission products to clarify the reaction background contribution, data were accumulated using the target mechanisms. To this end, the reaction energy around 200 MeV/nu- holder with no target inserted. cleon was chosen in the present study to observe differences in The reaction residues were measured by the ZeroDegree spec- the cross sections measured with the proton and deuteron tar- trometer with a full momentum acceptance (6%) and full an- gets, because the proton–proton interaction cross section (σpp) is gular acceptances in both the horizontal (90 mrad) and vertical significantly smaller than the proton–neutron (σpn) one at this re- (60 mrad) directions. In order to cover a broad range of spallation action energy. The high quality data of production cross sections products, several different magnetic rigidity (Bρ) settings were ap- for the interaction of LLFP with possible transmutation targets are plied: −9%, −6%, −3%, 0%, and +3% relative to the Bρ value of critical to converge towards a solution for transmutation of long- the secondary beam. Thus, a sufficient overlap was obtained for lived waste, as well as to verify the fragmentation and/or spallation neighboring settings. The momentum distributions of the products models. were obtained by the Bρ measurement at the dispersive focus of In this Letter, we report results from the first attempt to study the ZeroDegree spectrometer. After the secondary reactions, the the spallation reaction of the fission products 137Cs and 90Sr in width of the momentum distribution was less than 1%, which was the aspect of nuclear waste transmutation for LLFP. The inverse smaller than the momentum acceptance. The angular spreads of reaction technique was adopted in the present work: fast radioac- the products were estimated to be less than 6mrad (9 mrad) for tive beams of 137Cs and 90Sr, produced at the in-flight separa- the 137Cs (90Sr) case based on the Goldhaber model [16] including tor BigRIPS [10,11] of the RIKEN Radioactive Isotope Beam Fac- the deflection effect [17]. This model might give an overestima- tory (RIBF) [12], were used and proton/deuteron-induced reactions tion for the width of momentum distributions of products in both were conducted using proton and deuteron targets. The technique the proton- and deuteron-induced spallation reactions, as shown allows us to study systematically the target dependence of reac- in Refs. [4,18]. Thus, such angular spreads were much smaller than tions at an energy of ∼185 MeV/nucleon — the typical energy of the angular acceptance of the ZeroDegree spectrometer. For safety, beams delivered by the in-flight separator — and to identify unam- the momentum acceptance was limited to be p/p ≤±2.5% in biguously spallation products for isotopic production cross section the analysis to ensure the full acceptances in both angle and mo- measurements. In addition, the technique avoids the difficulties as- mentum [19] in each Bρ setting. sociated with using a highly radioactive target. The particle identification in the ZeroDegree spectrometer was achieved by measuring the time of flight (TOF), Bρ, energy loss 2. Experiment (E), and total kinetic energy (TKE). The TOF information was ob- tained between two plastic scintillators, one placed at the entrance The experiment was performed at RIBF, operated by RIKEN and the other at final focus of ZeroDegree. A trajectory reconstruc- Nishina Center and the Center for Nuclear Study, University of tion was applied to determine the B value using position and Tokyo.