A Demonstration test to separate minor actinides in high-level liquid waste by -hexaoctyl nitrilotriacetamide (HONTA) using mixer-settler extractors in a hot cell

Ban, Yasutoshi; Suzuki, Hideya*; Hotoku, Shinobu; Tsubata, Yasuhiro

Solvent Extraction Research and Development, Japan, 31(1), p.1 - 11, 2024/00

https://doi.org/10.15261/serdj.31.1

A demonstration test was performed to separate minor actinides (MA; Am and Cm) by -hexaoctyl nitrilotriacetamide (HONTA) as an extractant using mixer-settler extractors installed in a hot cell. A high-level liquid waste containing MA, and rare earths (RE; Y, La, Nd, and Eu) was used as the feed. HONTA diluted to 0.05 mol/dm in -dodecane was fed as the organic phase, and a part of the organic phase was reused without solvent regeneration. HONTA effectively extracted MA, whereas RE were less extractable. Consequently, the Y, La, Nd, and Eu ratios distributed to a RE fraction were 99.9%, 99.2%, 61.8%, and 81.4%, respectively. The Am and Cm ratios distributed to an MA fraction were 86.8% and 74.7%, respectively, and a substantial amount of MA (0.12 g) was recovered in the MA fraction by the end of the cumulative duration of 40 h.

Efficient separation of americium by a mixed solvent of two extractants, a diamideamine and a nitrilotriacetamide

Suzuki, Hideya*; Ban, Yasutoshi

Analytical Sciences, 39(8), p.1341 - 1348, 2023/08

https://doi.org/10.1007/s44211-023-00344-2

The Japan Atomic Energy Agency (JAEA) has proposed the Solvent Extraction from Liquid waste using Extractants of CHON-type for Transmutation (SELECT) process by solvent extraction as a new separation technology to recover minor actinides (MA) from high-level liquid waste (HLLW) produced by spent fuel reprocessing. The MA separation in the SELECT process comprises the batch recovery of MA and rare earths (RE) from HLLW, MA/RE separation, and Am/Cm separation. Three highly practical extractants are used in the MA separation. Furthermore, this flow configuration facilitates the preparation of nitric acid concentrations in the aqueous phase. However, the separation factor between Cm and Nd in the MA/RE separation is small ( = 2.5), requiring many extraction stages for continuous extraction in a mixer-settler. Therefore, this study investigated the separation of only Am from an aqueous nitric acid solution containing MA (Am and Cm) and RE using an organic phase mixed with two extractants alkyl diamideamine with 2-ethylhexyl alkyl chains (ADAAM(EH)) and hexa-n-octylnitrilotriacetamide (HONTA) used in the SELECT process. Under high-concentration nitric acid conditions, Am and La, Ce, Pr, Nd (light lanthanides) were extracted in the ADAAM(EH) + HONTA mixed solvent, whereas Cm, medium, and heavy lanthanides, and Y were partitioned in the aqueous phase. Subsequently, only light lanthanides could be back extracted from the ADAAM(EH) + HONTA mixture solvent containing Am and light lanthanides in low nitric acid concentrations. Furthermore, Am could be easily stripped with 0.2 M or 5 M nitric acid. This method does not require the mutual separation of Cm and Nd, which have low separation factors. Am can be efficiently separated by one extraction and two back-extractions, reducing the number of steps in the SELECT process.

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.

Lanthanide and actinide ion complexes containing organic ligands investigated by surface-enhanced infrared absorption spectroscopy

Hirata, Sakiko*; Kusaka, Ryoji; Meiji, Shogo*; Tamekuni, Seita*; Okudera, Kosuke*; Hamada, Shoken*; Sakamoto, Chihiro*; Honda, Takumi*; Matsushita, Kosuke*; Muramatsu, Satoru*; et al.

Inorganic Chemistry, 62(1), p.474 - 486, 2023/01

https://doi.org/10.1021/acs.inorgchem.2c03618

Chemistry of the elements at the end of the actinide series using their low-energy ion-beams

Sato, Tetsuya; Nagame, Yuichiro*

Radiochimica Acta, 110(6-9), p.441 - 451, 2022/07

https://doi.org/10.1515/ract-2022-0001

We describe our recent achievements in the effective production of low-energy ion-beams of the elements at the end of the actinide series, fermium (Fm, atomic number Z = 100), mendelevium (Md, Z = 101), nobelium (No, Z = 102), and lawrencium (Lr, Z = 103), using a surface ionization ion-source installed in the ISOL (Isotope Separator On-Line) at the Tandem accelerator facility of JAEA (Japan Atomic Energy Agency). Then the successful measurements of the first ionization potentials (IP) of these elements with the ISOL setup are reviewed. The measured IP values increased up to No via Fm and Md, while that of Lr was the lowest among the actinides. Based on the variation of the IP1 values of the heavy actinides with the atomic number in comparison with those of the heavy lanthanides, the results clearly demonstrated that the 5f orbitals are fully filled at No, and the actinide series ends with Lr. Furthermore, the IP value of Lr provoked controversy over its position in the Periodic Table, so a short introduction to this issue is presented. The feasibility of the extension of chemical studies to still heavier elements with their ion-beams generated by ISOL is briefly discussed.

The Chemistry of thorium, plutonium and MA

Sato, Nobuaki*; Kirishima, Akira*; Watanabe, Masayuki; Sasaki, Takayuki*; Uehara, Akihiro*; Takeda, Shino*; Kitatsuji, Yoshihiro; Otobe, Haruyoshi; Kobayashi, Taishi*

The Chemistry of Thorium, Plutonium and MA, 254 Pages, 2022/03

The chemistry of nuclear materials such as Thorium (Part 1) and Plutonium (Part 2) was described in relation from the fundamentals on solid chemistry and solution chemistry to the practicals on the experiment and evaluation method in detail. Minor actinides such as Neptunium, Americium, Curium and Protoactinium, was introduced the basics on the solid and solution chemistry.

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.

Density functional study aiming to elucidate separation mechanisms of minor actinides and rare earths

Kaneko, Masashi

Nihon Genshiryoku Gakkai-Shi ATOMO, 64(1), p.30 - 34, 2022/01

https://doi.org/10.3327/jaesjb.64.1_30

Partitioning of minor actinides from rare earths is one of the most important techniques to develop group separation of high-level radioactive liquid waste. In this issue, the results of prediction of separation performance between minor actinides and rare earths observed in solvent extraction and the separation mechanism by means of using density functional theory are explained.

Safety assessment of adsorbent for extraction chromatography and effect on radiation of separation operation

Miyazaki, Yasunori; Sano, Yuichi

Hoshasen Kagaku (Internet), (112), p.27 - 32, 2021/11

no abstracts in English