A Science-based mixed oxide property model for developing advanced oxide nuclear fuels

加藤 正人; 沖 拓海; 渡部 雅; 廣岡 瞬; Vauchy, R.; 小澤 隆之; 上羽 智之; 生澤 佳久; 中村 博樹; 町田 昌彦

Journal of the American Ceramic Society, 107(5), p.2998 - 3011, 2024/05

https://doi.org/10.1111/jace.19609

Herein, a science-based uranium and plutonium mixed oxide (MOX) property model (Sci-M Pro) is derived for determining properties of MOX fuel and analyzing their performance as functions of Pu content, minor-actinide content, oxygen-to-metal ratio, and temperature. The property model is constructed by evaluating the effect of phonons and electronic defects on heat capacity and thermal conductivity of MOX fuels. The effect of phonons was evaluated based on experimental datasets related to lattice parameter, thermal expansion, and sound speeds. Moreover, the effect of electronic defects was determined by analyzing oxygen-potential data based on defect chemistry. Furthermore, the model evaluated the effect of the Bredig transition on the thermal properties of MOX fuel by analyzing the irradiation test results. The derived property model is applied to the performance code to analyze fast reactor fuel pins.

Citizen science observation of a gamma-ray glow associated with the initiation of a lightning flash

鶴見 美和*; 榎戸 輝掲*; 一方井 祐子*; Wu, T.*; Wang, D.*; 篠田 太郎*; 中澤 知洋*; 辻 直樹*; Diniz, G.*; 片岡 淳*; et al.

Geophysical Research Letters, 50(13), p.e2023GL103612_1 - e2023GL103612_9, 2023/07

https://doi.org/10.1029/2023GL103612

Gamma-ray glows are observational evidence of relativistic electron acceleration due to the electric field in thunderclouds. However, it is yet to be understood whether such relativistic electrons contribute to the initiation of lightning discharges. To tackle this question, we started the citizen science "Thundercloud Project," where we map radiation measurements of glows from winter thunderclouds along Japan's sea coast area. We developed and deployed 58 compact gamma-ray monitors at the end of 2021. On 30 December 2021, five monitors simultaneously detected a glow with its radiation distribution horizontally extending for 2 km. The glow terminated coinciding with a lightning flash at 04:08:34 JST, which was recorded by the two radio-band lightning mapping systems, FALMA and DALMA. The initial discharges during the preliminary breakdown started above the glow, that is, in vicinity of the electron acceleration site. This result provides one example of possible connections between electron acceleration and lightning initiation.

Materials science and fuel technologies of uranium and plutonium mixed oxide

加藤 正人; 町田 昌彦; 廣岡 瞬; 中道 晋哉; 生澤 佳久; 中村 博樹; 小林 恵太; 小澤 隆之; 前田 宏治; 佐々木 新治; et al.

Materials Science and Fuel Technologies of Uranium and Plutonium mixed Oxide, 171 Pages, 2022/10

https://doi.org/10.1201/9781003298205

プルトニウム燃料を使用した革新的で先進的な原子炉が各国で開発されている。新しい核燃料を開発するためには、照射試験が不可欠であり、核燃料の性能と安全性を実証する必要がある。照射試験を補完する技術として、照射挙動を正確にシミュレートする技術を開発できれば、核燃料の研究開発にかかるコスト,時間,労力を大幅に削減でき、核燃料の照射挙動をシミュレーションすることで、安全性と信頼性を大幅に向上させることができる。核燃料の性能を評価するためには、高温での燃料の物理的および化学的性質を知る必要がある。そして、照射中に発生するさまざまな現象を記述した行動モデルの開発が不可欠である。以前の研究開発では、モデル開発の多くの部分で、フィッティングパラメータを使用した経験的手法が使用されてきた。経験的手法では、データがない領域では非常に異なる結果が得られる可能性がある。したがって、この研究では、燃料の基本的な特性を組成と温度に外挿できる科学的記述モデルを構築し、モデルが適用される照射挙動分析コードの開発を行った。

Critical slowing-down and field-dependent paramagnetic fluctuations in the skyrmion host EuPtSi; SR and NMR studies

比嘉 野乃花*; 伊藤 孝; 與儀 護*; 服部 泰佑; 酒井 宏典; 神戸 振作; Guguchia, Z.*; 髭本 亘; 中島 美帆*; 本間 佳哉*; et al.

Physical Review B, 104(4), p.045145_1 - 045145_7, 2021/07

https://doi.org/10.1103/PhysRevB.104.045145

We report the results of SR and Si NMR measurements carried out on the cubic chiral magnet EuPtSi. Our zero-field SR experiments revealed the development of critical slowing down of Eu spin fluctuations over a relatively wide critical region above . We also found from Si NMR that the spin fluctuations are strongly suppressed by magnetic field in the paramagnetic state above 20K. These characteristic spin dynamics observed over a wide region of temperature and magnetic field suggest the presence of magnetic frustration in the spin system. Such frustration would underlie the mechanism stabilizing the short-period skyrmion lattice observed in this compound.

Emergent spin-1 Haldane gap and ferroelectricity in a frustrated spin- ladder

上田 宏*; 小野田 繁樹*; 山口 泰弘*; 木村 剛*; 吉澤 大智*; 森岡 俊晶*; 萩原 政幸*; 萩原 雅人*; 左右田 稔*; 益田 隆嗣*; et al.

Physical Review B, 101(14), p.140408_1 - 140408_6, 2020/04

https://doi.org/10.1103/PhysRevB.101.140408

We report experimental and theoretical evidence that RbCuMoO has a nonmagnetic tetramer ground state of a two-leg ladder comprising antiferromagnetically coupled frustrated spin- chains and exhibits a Haldane spin gap of emergent spin-1 pairs. Three spin excitations split from the spin-1 triplet by a Dzyaloshinskii-Moriya interaction are identified in inelastic neutron-scattering and electron spin resonance spectra. A tiny magnetic field generates ferroelectricity without closing the spin gap, indicating a unique class of ferroelectricity induced by a vector spin chirality order.

High peak-current lightning discharges associated with downward terrestrial gamma-ray flashes

和田 有希*; 榎戸 輝揚*; 中村 佳敬*; 森本 健志*; 佐藤 光輝*; 牛尾 知雄*; 中澤 知洋*; 湯浅 孝行*; 米徳 大輔*; 澤野 達也*; et al.

Journal of Geophysical Research; Atmospheres, 125(4), p.e2019JD031730_1 - e2019JD031730_11, 2020/02

https://doi.org/10.1029/2019JD031730

During 2017-2018 winter operation of the Gamma-Ray Observation of Winter Thunderclouds experiment in Japan, two downward terrestrial gamma-ray flashes (TGFs) that triggered atmospheric photonuclear reactions were detected. They took place during winter thunderstorms on 5 December 2017 and 9 January 2018 at Kanazawa, Ishikawa Prefecture, Japan. Each event coincided with an intracloud/intercloud discharge, which had a negative-polarity peak current higher than 150 kA. Their radio waveforms in the low-frequency band are categorized as a distinct lightning type called energetic in-cloud pulse (EIP). Negative-polarity EIPs have been previously suggested to be highly associated with downward TGFs, and the present observations provide evidence of the correlation between them for the first time. Furthermore, both of the downward TGFs followed gamma-ray glows, minute-lasting high-energy emissions from thunderclouds. It is suggested that the negative EIPs took place with downward propagating negative leaders or upward positive ones developed in highly electrified regions responsible for the gamma-ray glows.

Gamma-ray glow preceding downward terrestrial gamma-ray flash

和田 有希*; 榎戸 輝揚*; 中村 佳敬*; 古田 禄大; 湯浅 孝行*; 中澤 知洋*; 森本 健志*; 佐藤 光輝*; 松元 崇弘*; 米徳 大輔*; et al.

Communications Physics (Internet), 2(1), p.67_1 - 67_9, 2019/06

https://doi.org/10.1038/s42005-019-0168-y

Two types of high-energy events have been detected from thunderstorms. One is "terrestrial gamma-ray flashes" (TGFs), sub-millisecond emissions coinciding with lightning discharges. The other is minute-lasting "gamma-ray glows". Although both phenomena are thought to originate from relativistic runaway electron avalanches in strong electric fields, the connection between them is not well understood. Here we report unequivocal simultaneous detection of a gamma-ray glow termination and a downward TGF, observed from the ground. During a winter thunderstorm in Japan on 9 January 2018, our detectors caught a gamma-ray glow, which moved for 100 s with ambient wind, and then abruptly ceased with a lightning discharge. Simultaneously, the detectors observed photonuclear reactions triggered by a downward TGF, whose radio pulse was located within 1 km from where the glow ceased. It is suggested that the highly-electrified region producing the glow was related to the initiation of the downward TGF.

Termination of electron acceleration in thundercloud by intracloud/intercloud discharge

和田 有希*; Bowers, G. S.*; 榎戸 輝揚*; 鴨川 仁*; 中村 佳敬*; 森本 健志*; Smith, D.*; 古田 禄大*; 中澤 知洋*; 湯浅 孝行*; et al.

Geophysical Research Letters, 45(11), p.5700 - 5707, 2018/06

https://doi.org/10.1029/2018GL077784

An on-ground observation program for high energy atmospheric phenomena in winter thunderstorms along Japan Sea has been performed via lightning measurements of -ray radiation, atmospheric electric field and low-frequency radio band. On February 11, 2017, the radiation detectors recorded -ray emission lasting for 75 sec. The -ray spectrum extended up to 20 MeV and was reproduced by a cutoff power-law model with a photon index of 1.36, being consistent with a Bremsstrahlung radiation from a thundercloud (as known as a -ray glow). Then the -ray glow was abruptly terminated with a nearby lightning discharge. The low-frequency radio monitors, installed 50 km away from Noto School, recorded intra/inter-cloud discharges spreading over 60km area with a 300 ms duration. The timing of the -ray termination coincided with the moment when a sequence of intra/inter-cloud discharges passed 0.7 km horizontally away from the radiation monitors. The atmospheric electric-field measurement presented that negative charge was located in the cloud base and not neutralized by the lightning discharge. This indicates that the -ray source was located at an higher region than the cloud base.

Defect chemistry and basic properties of non-stoichiometric PuO

加藤 正人; 中村 博樹; 渡部 雅; 松本 卓; 町田 昌彦

Defect and Diffusion Forum, 375, p.57 - 70, 2017/05

http://doi.org/10.4028/www.scientific.net/DDF.375.57

PuOの実験データをレビューし、酸素ポテンシャル、電気伝導率及び第一原理計算結果を用いて欠陥濃度を評価した。欠陥濃度を評価する式を導出し、様々な基礎特性の間の整合性を確認するとともに、熱物性を評価するための機構論的モデルを導出した。

東京電力福島第一原子力発電所の炉内構造物解体を想定したプラズマ切断技術による適用性試験

手塚 将志; 中村 保之; 岩井 紘基; 佐野 一哉

JAEA-Technology 2015-047, 114 Pages, 2016/03

JAEA-Technology-2015-047.pdf:46.17MB

東京電力福島第一原子力発電所は、炉心溶融に伴い炉内構造物は原形を留めておらず、溶融燃料と混在し複雑狭隘な状態にあると想定される。このため「ふげん」では溶融再凝固した炉内構造物の取出しに向けて、2012年度から3カ年で、プラズマアーク切断技術を用いた切断試験を進めてきており、炉内構造物等の取出しに有効な工法であることを確認した。具体的には、原子炉構造材を模擬した試験体を用いた要素試験を実施し、対象物に応じて切断条件の最適化を図ることにより、溶断ドロス発生の抑制が可能であることを確認した。また、格納容器下部等に堆積していると想定される厚みが不明な燃料デブリに対し、対象を事前に加熱することで切断能力の向上を図る手法を構築した。さらに、プラズマアークで切断不可能なセラミック等の非導電材も切断可能なプラズマジェットと組み合わせた連携切断手法により、燃料デブリと溶融金属の混合材(模擬試験体)でも切断が可能であることを確認した。これらの成果から、プラズマ切断技術は、種々の条件に応じた最適な切断条件を設定することにより、燃料デブリ及び炉内溶融金属の取出し作業へ適用できる見通しを得た。