Determination of Sr in highly radioactive aqueous samples via conversion to a kinetically stable 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid complex followed by concentration-separation-fractionation based on capillary electrophoresis-liquid scintillation

大内 和希; 原賀 智子; 廣瀬 和生*; 黒澤 結香*; 佐藤 義行; 渋川 雅美*; 齋藤 伸吾*

Analytica Chimica Acta, 1298, p.342399_1 - 342399_7, 2024/04

https://doi.org/10.1016/j.aca.2024.342399

従来の高線量試料分析法では被ばくリスクが高く、大量の二次放射性廃棄物が発生することから、放射線放出量を低減できる迅速な分析法が強く望まれている。このニーズに取り組むため、我々は液体シンチレーションカウンティングと2点検出によるキャピラリー過渡的等速電気泳動(ctITP)を組み合わせたSr定量法を開発した。これは、1,4,7,10-テトラアザシクロドデカン-1,4,7,10-テトラ酢酸(DOTA)-Sr錯体を1回の操作で分離・分画する方法である。高線量の放射性試料をマイクロリットルレベルで取り扱うことができ、従来のイオン交換法よりも大幅に高速であるこの方法により、実高線量廃棄物中のSrを選択的に定量した。ctITPにおける濃縮・分離の成功は、Sr-DOTA錯体が解離不活性であることに起因する。

Field-induced insulator-metal transition in EuTe

竹内 徹也*; 本多 史憲*; 青木 大*; 芳賀 芳範; 木田 孝則*; 鳴海 康雄*; 萩原 政幸*; 金道 浩一*; 軽部 皓介*; 播磨 尚朝*; et al.

Journal of the Physical Society of Japan, 93(4), p.044708_1 - 044708_10, 2024/04

https://doi.org/10.7566/JPSJ.93.044708

Electrical and magnetic properties of divalent europium antiferromagnet EuTe are studied on single crystals grown from Te-flux method. Antiferromagnetism occurs at 11 K with an insulating ground state. Application of magnetic field induces a sudden resistance drop leading to a phase transition to metallic state. Energy band calculations reveal the appearance of a Fermi surface pocket with Te-5p character induced by the polarized Eu moments.

放射性微粒子の基礎物性解明による廃炉作業リスク低減への貢献(委託研究); 令和2年度英知を結集した原子力科学技術・人材育成推進事業

廃炉環境国際共同研究センター; 茨城大学*

JAEA-Review 2023-021, 112 Pages, 2024/02

JAEA-Review-2023-021.pdf:7.1MB

日本原子力研究開発機構(JAEA)廃炉環境国際共同研究センター(CLADS)では、令和2年度英知を結集した原子力科学技術・人材育成推進事業(以下、「本事業」という。)を実施している。本事業は、東京電力ホールディングス株式会社福島第一原子力発電所の廃炉等をはじめとした原子力分野の課題解決に貢献するため、国内外の英知を結集し、様々な分野の知見や経験を、従前の機関や分野の壁を越えて緊密に融合・連携させた基礎的・基盤的研究及び人材育成を推進することを目的としている。平成30年度の新規採択課題から実施主体を文部科学省からJAEAに移行することで、JAEAとアカデミアとの連携を強化し、廃炉に資する中長期的な研究開発・人材育成をより安定的かつ継続的に実施する体制を構築した。本研究は、平成30年度に採択された研究課題のうち、「放射性微粒子の基礎物性解明による廃炉作業リスク低減への貢献」の平成30年度から令和3年度分の研究成果について取りまとめたものである(令和3年度まで契約延長)。本研究は、東京電力株式会社福島第一原子力発電所事故で環境へ放出された放射性セシウム(Cs)を高濃度に含有する、不溶性の性状を持つシリカ(SiO)主材微粒子の基礎的な物性(粒径、組成、同位体組成、静電特性、光学特性)や放射体の濃度等について、一定の成果をもつ我が国の放射化学、分析化学、エアロゾルの科学者らが英知を集め英国側と協力して更に研究を進め、炉内事故事象の解明、生成要因の解明を行い、廃炉手順の確立、溶融燃料等の回収、作業員、現場・周辺環境の安全確保等の達成に寄与することをねらいとした。

Estimation method for residual sodium amount on unloaded dummy fuel assembly

河口 宗道; 平川 康; 杉田 裕亮; 山口 裕

Nuclear Technology, 210(1), p.55 - 71, 2024/01

https://doi.org/10.1080/00295450.2023.2214261

本研究はもんじゅ模擬燃料集合体における残留ナトリウム膜及び塊の評価手法を開発し、実験的にピンの間のギャップを通ってナトリウムが流れる様子を確認した。ピン表面の残留ナトリウムの量は3種類の試験体((a)単ピン,(b)7本ピン集合体,(c)169本ピン集合体)を使って測定した。実験では、ピンの引き抜き速度やナトリウム濡れ性の改善により、残留ナトリウム量が劇的に増加することを明らかにした。さらに、169本ピンの実験により、短尺であるが模擬燃料集合体の実効的な残留ナトリウム量を測定し、模擬燃料集合体を通って流れるナトリウムの振舞いを確認した。開発した予測手法は、4つのモデル(粘性流れモデル、Landau-Levich-Derjaguin(LLD)モデル、Brethertonモデルに関わる実験式、管内の毛細管力モデル)から構築されており、その計算結果は実験の残留ナトリウム量と同程度な結果を与えた。ただし、ナトリウム濡れ性の不確かさはLLDモデルの予測値の約1.8倍である。この予測手法を使って、もんじゅの模擬燃料集合体に残留するナトリウム量を評価することができる。

Understanding muon diffusion in perovskite oxides below room temperature based on harmonic transition state theory

伊藤 孝; 髭本 亘; 下村 浩一郎*

Physical Review B, 108(22), p.224301_1 - 224301_11, 2023/12

https://doi.org/10.1103/PhysRevB.108.224301

In positive muon spin rotation and relaxation (SR) spectroscopy, positive muons () implanted into solid oxides are conventionally treated as immobile spin-probes at interstitial sites below room temperature. This is because each is thought to be tightly bound to an oxygen atom in the host lattice to form a muonic analogue of the hydroxy group. On the basis of this concept, anomalies in SR spectra observed in oxides have been attributed in most cases to the intrinsic properties of host materials. On the other hand, global diffusion with an activation energy of 0.1~eV has been reported in some chemically-substituted perovskite oxides at cryogenic temperatures, although the reason for the small activation energy despite the formation of the strong O bond has not yet been quantitatively understood. In this study, we investigated interstitial diffusion in the perovskite oxide lattice using KTaO cubic perovskite as a model system. We used the SR method and density functional theory calculations along with the harmonic transition state theory to study this phenomenon both experimentally and theoretically. Experimental activation energies for global diffusion obtained below room temperature were less than a quarter of the calculated classical potential barrier height for a bottleneck transfer path. The reduction in the effective barrier height could be explained by the harmonic transition state theory with a zero-point energy correction; a significant difference in zero-point energies for at the positions in the O bonding equilibrium state and a bond-breaking transition state was the primary cause of the reduction. This suggests that the assumption of immobile in solid oxides is not always satisfied since such a significant decrease in diffusion barrier height can also occur in other oxides.

Predictive and inverse modeling of a radionuclide diffusion experiment in crystalline rock at ONKALO (Finland)

Soler, J. M.*; Keklinen, P.*; Pulkkanen, V.-M.*; Moreno, L.*; Iraola, A.*; Trinchero, P.*; Hokr, M.*; ha, J.*; Havlov, V.*; Trpkoov, D.*; et al.

Nuclear Technology, 209(11), p.1765 - 1784, 2023/11

https://doi.org/10.1080/00295450.2023.2209234

The REPRO-TDE test was performed at a depth of about 400 m in the ONKALO underground research facility in Finland. Synthetic groundwater containing radionuclide tracers (HTO, Cl-36, Na-22, Ba-133, Cs-134) was circulated for about four years in a packed-off interval of the injection borehole. Tracer activities were additionally monitored in two observation boreholes. The test was the subject of a modelling exercise by the SKB GWFTS Task Force. Eleven teams participated in the exercise, using different model concepts and approaches. Predictive model calculations were based on laboratory-based information concerning porosities, diffusion coefficients and sorption partition coefficients. After the experimental results were made available, the teams were able to revise their models to reproduce the observations. General conclusions from these back-analysis calculations include the need for reduced effective diffusion coefficients for Cl-36 compared to those applicable to HTO (anion exclusion), the need to implement weaker sorption for Na-22, compared to results from laboratory batch-sorption experiments, and the observation of large differences between the theoretical initial concentrations for the strongly-sorbing Ba-133 and Cs-134 and the first measured values a few hours after tracer injection. Different teams applied different concepts, concerning mainly the implementation of isotropic vs. anisotropic diffusion, or the possible existence of Borehole Disturbed Zones around the different boreholes. The role of microstructure was also addressed in two of the models.

Pd nanoparticles on the outer surface of microporous aluminosilicates for the direct alkylation of benzenes using alkanes

美崎 慧*; 三輪 寛子*; 伊藤 孝; 吉田 健文*; 長谷川 慎吾*; 中村 由紀奈*; 徳竹 駿太*; 高畠 萌*; 下村 浩一郎*; Chun, W.-J.*; et al.

ACS Catalysis, 13(18), p.12281 - 12287, 2023/09

https://doi.org/10.1021/acscatal.3c02309

The direct alkylation of benzenes with simple alkanes is one of the ideal processes for the production of alkylbenzenes. We demonstrated that Pd nanoparticles on the outer surface of H-ZSM-5 are efficient catalysts for direct alkylation. The reaction proceeds through the activation of an alkane on the acid sites present inside the zeolite pores. This process is followed by the nucleophilic addition of an arene to the activated alkane. The spillover of the abstracted hydrogen atoms from the acid sites to the Pd nanoparticles on the outer surface accelerates recombination to H. A maximum toluene conversion of 58.5% and selectivity of 95.6% for the alkylated products are achieved when toluene is reacted with -heptane. -selective alkylation is achieved, due to the effect of the pore size of H-ZSM-5. The SR study of muonium, a pseudo-isotope of hydrogen, in aluminosilicates suggested that the formation of atomic hydrogen is possible and its lifetime is in the sub-microsecond range or longer, which is long enough for chemical reactions.

Radiation imaging of a highly contaminated filter train inside Fukushima Daiichi Nuclear Power Station Unit 2 using an integrated Radiation Imaging System based on a Compton camera

佐藤 優樹; 寺阪 祐太

Journal of Nuclear Science and Technology, 60(8), p.1013 - 1026, 2023/08

https://doi.org/10.1080/00223131.2022.2159894

The Fukushima Daiichi Nuclear Power Station (FDNPS) suffered a meltdown in the aftermath of the large tsunami caused by the Great East Japan Earthquake that occurred on 11 March 2011. A massive amount of radioactive substance was spread over a wide area both inside and outside the FDNPS site. In this study, we present an approach for visualizing a radioactive hotspot on a standby gas-treatment system filter train, a highly contaminated piece of equipment in the air-conditioning room of the Unit 2 reactor building of FDNPS, using radiation imaging based on a Compton camera. In addition to fixed-point measurements using only the Compton camera, data acquisition while moving using an integrated Radiation Imaging System (iRIS), which combines a Compton camera with a simultaneous localization and mapping device and a survey meter, enabled the three-dimensional visualization of the hotspot location on the filter train. In addition, we visualized the hotspot and quantitatively evaluated its radioactivity. Notably, the visualized hotspot location and estimated radioactivity value are consistent with the accident investigation report of the FDNPS. Finally, the extent to which the radioactivity increased the ambient dose equivalent rate in the surrounding environment was explored.

Chiral symmetry restoration at high matter density observed in pionic atoms

西 隆博*; 橋本 直; 他46名*

Nature Physics, 19(6), p.788 - 793, 2023/06

https://doi.org/10.1038/s41567-023-02001-x

According to quantum chromodynamics, vacuum is not an empty space, because it is filled with quark-antiquark pairs. The pair has the same quantum numbers as the vacuum and forms a condensate because the strong interaction of the quantum chromodynamics is too strong to leave the vacuum empty. This quark-antiquark condensation, the chiral condensate, breaks the chiral symmetry of the vacuum. The expectation value of the chiral condensate is an order parameter of the chiral symmetry, which is expected to decrease at high temperatures or high matter densities where the chiral symmetry is partially restored. Head-on collisions of nuclei at ultra-relativistic energies have explored the high-temperature regime, but experiments at high densities are rare. Here we measure the spectrum of pionic Sn atoms and study the interaction between the pion and the nucleus. We find that the expectation value of the chiral condensate is reduced at finite density compared to the value in vacuum. The reduction is linearly extrapolated to the nuclear saturation density and indicates that the chiral symmetry is partially restored due to the extremely high density of the nucleus.

Research on improvement of HTGR core power-density, 4; Feasibility study for a reactor core

沖田 将一朗; 水田 直紀; 高松 邦吉; 後藤 実; 吉田 克己*; 西村 洋亮*; 岡本 孝司*

Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 10 Pages, 2023/05

Adoption of SiC-matrix fuel elements in future pin-in-block type HTGR designs will enhance oxidation resistance of the fuel element in the event of the air ingress accident, one of the most worrisome accidents in HTGRs. This would eliminate the need for the graphite sleeves used in the current pin-in-block type HTGR designs and enable high power density core designs with sleeveless and direct coolable fuel structure. Such a concept itself has been suggested by Japan Atomic Energy Agency (JAEA) in the past. However, JAEA has not yet demonstrated the feasibility for a core design with the SiC-matrix fuel elements. The present work is intended to demonstrate the feasibility for a new core design upgraded from an existing conceptual core design, called HTR50S, with 50 MW thermal power and reactor outlet temperature of 750C. The new core design uses SiC-matrix fuel elements and increases the reactor power density to 1.2 times higher than the original HTR50S design. The feasibility is determined by whether the core satisfies the target values in nuclear and thermal-hydraulic designs by performing burn-up calculation with the whole core model and fuel temperature calculations. The calculation results showed that the new core design satisfied these target values on the reactor shutdown margin, the temperature coefficient of reactivity, and the maximum fuel temperature during normal operation.