Effect of decay heat on pyrochemical reprocessing of minor actinide transmutation nitride fuels

Hayashi, Hirokazu; Tsubata, Yasuhiro; Sato, Takumi

Nihon Genshiryoku Gakkai Wabun Rombunshi (Internet), 22(3), p.97 - 107, 2023/08

https://doi.org/10.3327/taesj.J22.009

The Japan Atomic Energy Agency has chosen nitride fuel as the first candidate for the transmutation of long-lived minor actinides (MA) using accelerator-driven systems (ADS). The pyrochemical method has been considered for reprocessing spent MA nitride fuels, because their decay heat should be very large for aqueous reprocessing. This study was conducted to investigate the effect of decay heat on the pyrochemical reprocessing of MA nitride fuels. On the basis of the estimated decay heats and the temperature limits of the materials that are to be handled in pyrochemical reprocessing, quantities adequate for handling in argon gas atmosphere were evaluated. From these considerations, we proposed that an electrorefiner with a diameter of 26 cm comprising 12 cadmium (Cd) cathodes with a diameter of 4 cm is suitable. On the basis of the size of the electrorefiner, the number necessary to reprocess spent MA fuels from 1 ADS in 200 days was evaluated to be 25. Furthermore, the amount of Cd-actinides (An) alloy to produce An nitrides by the nitridation-distillation combined reaction process was proposed to be about one-quarter that of Cd-An cathode material. The evaluated sizes and required numbers of equipment support the feasibility of pyrochemical reprocessing for MA nitride fuels.

Formation of MPd (M = Gd, Np) by the reaction of MN with Pd and chlorination of MPd using cadmium chloride

Hayashi, Hirokazu; Shibata, Hiroki; Sato, Takumi; Otobe, Haruyoshi

Journal of Radioanalytical and Nuclear Chemistry, 332(2), p.503 - 510, 2023/02

https://doi.org/10.1007/s10967-023-08760-4

The formation of MPd (M = Gd, Np) by the reaction of MN with Pd at 1323 K in Ar gas flow was observed. Cubic AuCu-type GdPd ( = 0.4081 0.0001 nm) and NpPd ( = 0.4081 0.0001 nm) were identified, respectively. The product obtained from the reaction of NpN with Pd contained additional phases including the hexagonal TiNi-type NpPd. Chlorination of the MPd (M = Gd, Np) samples was accomplished by the solid-state reaction using cadmium chloride at 673 K in a dynamic vacuum. Pd-rich solid solution phase saturated with Cd and an intermetallic compound PdCd were obtained as by-products of MCl formation.

Electrochemical recovery of Zr and Cd from molten chloride salts for reprocessing of used nitride fuels

Murakami, Tsuyoshi*; Hayashi, Hirokazu

Journal of Nuclear Materials, 558, p.153330_1 - 153330_7, 2022/01

https://doi.org/10.1016/j.jnucmat.2021.153330

Excess amounts of dissolution agents, CdCl and ZrCl, are required to dissolve transuranium (TRU: Pu and minor actinides) nitrides into LiCl-KCl melts at the chemical dissolution step, which is the first step in the reprocessing of used nitride fuels. We propose an electrochemical process where the remaining Zr and Cd are recovered from the melts to be recycled as dissolution agents for the chemical dissolution step, leaving TRU in the melts. Since the initial concentration ratio of CdCl/ZrCl remaining in the melts would depend on the condition of the chemical dissolution step and would vary during the proposed electrochemical recovery process, electrochemical behaviors of Zr and Cd were investigated in LiCl-KCl melts with various concentration ratios of CdCl/ZrCl at 723 K to confirm the basic feasibility of the proposed process. Potentiostatic electrolysis was performed using a liquid Cd cathode at -1.05 V (vs. Ag/AgCl), which was a more positive potential than the redox potentials of TRU on the liquid Cd electrode. The obtained results showed that the current efficiency for recovering Zr and Cd from the melts was as high as 100% regardless of the CdCl/ZrCl concentration ratio in the melts.

Design and demonstration of the prototype nitrogen circulation refining system for nitride fuel fabrication (Contract research)

Iwasa, Toma; Takano, Masahide

JAEA-Technology 2020-024, 29 Pages, 2021/03

JAEA-Technology-2020-024.pdf:2.33MB

Partitioning and transmutation of minor actinides (MA) is an important issue to reduce volume and radio-toxicity of high-level radioactive wastes. In Nuclear Science Research Institute, we have been carrying out R&D on MA-bearing nitride fuel for accelerator driven system. In the actual nitride fuel fabrication process, a special nitrogen gas highly enriched with N is required to avoid C production from N by (n,p) reaction in the fuel. For the economical use of such expensive gas, we need a nitrogen circulation refining system that can remove carbon monoxide (CO) evolved by carbothermic nitridation of oxides and can use the nitrogen gas in the closed system without loss. To develop the system, at first we listed up the performance requirements, and then designed and assembled a prototype system for laboratory-scale demonstration. The system consists of CO removal unit and circulation unit that can automatically keep the system pressure and the gas flow rate constant. As a result of demonstration on the nitridation of oxide, both units completely satisfy the requirements. We confirmed that the concept can be applied to the actual fuel fabrication with further additional function such as automatic hydrogen feed for the control of decarburization.

Material balance evaluation of pyroprocessing for minor actinide transmutation nitride fuel

Tateno, Haruka; Sato, Takumi; Tsubata, Yasuhiro; Hayashi, Hirokazu

Journal of Nuclear Science and Technology, 57(3), p.224 - 235, 2020/03

https://doi.org/10.1080/00223131.2019.1666056

Fuel cycle technology for the transmutation of long-lived minor actinides (MAs) using an accelerator-driven system has been developed using the double-strata fuel cycle concept. A mononitride solid solution of MAs and Pu diluted with ZrN is a prime fuel candidate for the accelerator-driven transmutation of MAs. Pyro-reprocessing is suitable for recycling the residual MAs in irradiated nitride fuel with high radiation doses and decay heat. Spent nitride fuel is anodically dissolved, and the actinides are recovered simultaneously into a liquid cadmium cathode via molten salt electrorefining. The process should be designed to achieve the target recovery yield of MAs and the acceptable impurity level of rare earths in the recovered material. We evaluated the material balance during the pyro-reprocessing of spent nitride fuel to gain important insight on the design process. We examined the effects of changing processing conditions on material flow and quantity of waste.

Dissolution and chemical analysis of Zr-based lanthanide nitrides

Hayashi, Hirokazu; Chiba, Rikiya*

Progress in Nuclear Science and Technology (Internet), 5, p.196 - 199, 2018/11

https://doi.org/10.15669/pnst.5.196

Uranium-free nitride fuel has been chosen as the first candidate for transmutation of long-lived minor actinides (MA: Np, Am, Cm) using sub-critical accelerator-driven system (ADS) under the double strata fuel cycle concept by Japan Atomic Energy Agency (JAEA). Dissolution behavior of ZrN-based nitrides in nitric acid is examined using lanthanides as surrogate materials of TRU elements. Chemical analysis of the ZrN-based lanthanide nitrides dissolved in nitric acid is also carried out.

Present state of partitioning and transmutation of long-lived nuclides, 4; Transmutation system using accelerator driven system and technology maturity of partitioning and transmutation

Tsujimoto, Kazufumi; Arai, Yasuo; Minato, Kazuo

Nihon Genshiryoku Gakkai-Shi ATOMO, 59(11), p.644 - 648, 2017/11

no abstracts in English

Chapter 4, Technology on transmutation fuels and targets, 4.1 Fuel fabrication technology, 4.1.4 Nitride fuel (Double-strata concept with ADS), 4.1.5 The other fuels and targets, 4.2 Evaluation of fuel behavior, 4.2.4 Nitride fuel (Double-strata concept with ADS), 4.2.5 The other fuels and targets

Arai, Yasuo

Bunri Henkan Gijutsu Soron, p.134 - 146, 2016/08

no abstracts in English

Recent progress and future R&D plan of nitride fuel cycle technology for transmutation of minor actinides

Hayashi, Hirokazu; Nishi, Tsuyoshi; Takano, Masahide; Sato, Takumi; Shibata, Hiroki; Kurata, Masaki

NEA/NSC/R(2015)2 (Internet), p.360 - 367, 2015/06

https://www.oecd-nea.org/science/docs/2015/nsc-r2015-2.pdf#page=362

Uranium-free nitride fuel was chosen as the first candidate for transmutation of long-lived minor actinides (MA) using accelerator-driven system (ADS) under the double strata fuel cycle concept by Japan Atomic Energy Agency (JAEA). The advantages of nitride fuel are good thermal properties and large mutual solubility among actinide elements. A pyrochemical process is proposed as the first candidate for the reprocessing of the spent nitride fuel, because this technique has some advantages over aqueous process, such as the resistance to radiation damage, which is an important issue for the fuels containing large amounts of highly radioactive MA. This paper overviews the recent progress and future R&D plan of the study on the nitride fuel cycle technology in JAEA.

Status and future plan of research and development on partitioning and transmutation technology for long-lived nuclides in JAERI

Oigawa, Hiroyuki; Nishihara, Kenji; Minato, Kazuo; Kimura, Takaumi; Arai, Yasuo; Morita, Yasuji; Nakayama, Shinichi; Katakura, Junichi

JAERI-Review 2005-043, 193 Pages, 2005/09

JAERI-Review-2005-043.pdf:16.13MB

JAERI has been conducting research and development on partitioning and transmutation (P&T) technology for long-lived nuclides to develop the double-strata fuel cycle concept, in accordance with the Atomic Energy Commission's "Research and Development of Technologies for Partitioning and Transmutation of Long-lived Nuclides - Status and Evaluation Report" issued in 2000. The double-strata fuel cycle concept consists of four major processes: partitioning, fuel fabrication, transmutation, and fuel processing. The five-year achievement and future perspectives for the technology on these processes are presented in this report. It also provides an analytical study on impacts of introducing P&T technology on waste management, and on deployment of P&T for the future nuclear energy system.