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Francisco, P. C. M.; 松村 大樹; 菊池 亮佑*; 石寺 孝充; 舘 幸男
Environmental Science & Technology, 56(5), p.3011 - 3020, 2022/03
被引用回数：2 パーセンタイル：27.6(Engineering, Environmental)The radionuclide selenium-79 (Se-79) is predicted to be a key contributor to the long-term radiologic hazards associated with geological high-level waste (HLW) repositories, hence its release is of pertinent concern in the safety assessment of repositories. In this study, we examined the immobilization mechanisms of Se(-II)-prevalent under anoxic and reducing repository conditions-during interaction with aqueous Fe(II) and freshly precipitated Fe(OH)
at circumneutral and alkaline conditions, respectively, its response to changes in pH, and its behavior during aging at 90
C. Using microscopic and spectroscopic techniques, we observed that Se(-II) was readily immobilized via iron selenide precipitation regardless of whether Se(-II) reacts with aqueous species or solid phases and that modifying the pH following initial immobilization did not immediately remobilize Se(-II). These observations indicate that Se(-II) migration beyond the overpack can be effectively and rapidly retarded via interaction with Fe(II) species arising from overpack corrosion. Thermodynamic calculations, however, showed that at alkaline conditions, iron selenides immediately became metastable and will likely dissolve in the long term. Aging experiments at 90C showed that Se(-II) can be completely retained via the crystallization of ferroselite at circumneutral conditions, while it will be largely remobilized at alkaline conditions. Our results show that Se(-II) mobility can be significantly influenced by its interactions with the corrosion products of the steel overpack and that these behaviors will have to be considered in repository safety assessments.
本多 充; 菊池 満; 安積 正史*
Nuclear Fusion, 52(2), p.023021_1 - 023021_12, 2012/02
被引用回数：23 パーセンタイル：69.27(Physics, Fluids & Plasmas)The collisionality dependence on a shielding factor of a neutral beam driven current, which is generally neglected for most models currently used, is shown to be important especially for plasma parameters comparable to those of present-day tokamak experiments. Here, the shielding factor is defined as the ratio of the beam driven current to the fast-ion circulating current. An addition of friction coefficients involving beam ions to the matrix inversion method based on the moment approach readily makes it possible to estimate the collisionality-dependent shielding factor. The collisionality-dependent models proposed coincide with the collisionless model in the collisionless limit. They clearly elucidate the strong dependence of the shielding factor on collisionality: Increasing collisionality certainly decreases the shielding factor. This finding indicates that using a collisionless model always overestimates a beam driven current, more or less.
石寺 孝充; Xia, X.*; 出光 一哉*; 菊池 芳郎*
Journal of Nuclear Science and Technology, 45(8), p.763 - 772, 2008/08
被引用回数：6 パーセンタイル：39.98(Nuclear Science & Technology)オーバーパック腐食生成物が圧縮ベントナイト中の放射性核種の収着挙動,拡散挙動へ及ぼす影響を調べるため、あらかじめ電解腐食させた炭素鋼を圧縮ベントナイトに接触させて鉄腐食生成物をベントナイト中へ移行させ、圧縮ベントナイト間隙中の鉄腐食生成物の存在形態を調べた。圧縮ベントナイトをスライスし、スライス片の選択溶解抽出を行い鉄腐食生成物の結晶化の程度を調べ、鉄腐食生成物の価数を調べた結果、室温で数年の範囲内では、鉄腐食生成物は非晶質のFe(OH)及びFe(OH)
として存在していることが推測された。XRD分析の結果より、鉄腐食生成物によってNa型スメクタイトのFe型化はほとんど起こっておらず、鉄腐食生成物はスメクタイト粒子間に存在していることが示唆された。また、あらかじめ大気下で生成した3価の鉄腐食生成物は、圧縮ベントナイト間隙中では容易に2価に還元されないものと考えられた。
伊藤 谷生*; 津村 紀子*; 竹内 章*; 石丸 恒存; 高見 明*; 井川 秀雅*; 駒田 希充*; 山本 修治*; 菊池 伸輔*; 宮内 崇裕*; et al.
Geodynamics of Atotsugawa Fault System, p.17 - 24, 2007/00
1995年の兵庫県南部地震以降、地震発生域における活断層の構造解明に関心が拡がる中で、地下構造解明の有力な手段である反射法地震探査を高角な断層に適用する方法の開発が急務となっていた。こうして、詳細な地下構造情報が得られている神岡鉱山を通過する茂住祐延断層をターゲットに1995年11月、準3次元的な反射法探査の実験が行われたのである。実験は、同断層が走向N65E,傾斜84SEであることを明らかにしたが、同時により詳細な構造解明のためには、オフライン型レコーダの新規開発が必要であることも示した。これを受けて2002年までに同レコーダの開発が行われ、その後の地震探査における強力な武器となっている。この意味で同実験はパイオニアの役割を果たしたのである。
中山 武*; 山本 正弘; 阿部 充志*; 柴田 孝俊; 大塚 道夫*; 秋山 隆*; 佐藤 勝利*; 菊池 一夫; 和田 豊*; 小池 常之; et al.
Proceedings of the 18th IEEE/NPSS Symposium on Fusion Engineering (SOFE '99), p.227 - 230, 1999/10
高性能トカマク開発試験装置(JFT-2M)では、将来の炉構造材料の候補である強磁性体の低放射化フェライト鋼F82H(以下フェライト鋼と記す)を用いた先進材料プラズマ試験計画を段階的に進めている。第1段階のリップル低減試験では、フェライト鋼板を真空容器の外部に設置して、トロイダル磁場リップルの低減を図る。本発表は、このフェライト鋼板の機械設計に関するものである。フェライト鋼板の形状は、各トロイダルセクション毎に決定し、ポート、計測器、ベーキングヒータ等を避けた中で最もリップルを低減できる構造とした。フェライト鋼板は、トロイダル磁場コイルケースから支持し、支持構造は可能な通電パターンすべてに対する電磁力を考慮して決定した。また、板厚はトロイダル磁場強度に応じて可変とした。設置後に電磁力試験を実施し、支持具の健全性を確認できた。フェライト鋼板の設置により、トロイダル磁場リップルの基本モードを2.1%から0.8%に低減できた。
山本 洋一; 向山 武彦; 菊池 充*; 若原 道夫*; 大熊 輝夫*
第14回核物質管理学会 (INMM)日本支部年次大会論文集, p.131 - 137, 1993/11
コブラ封印は、現場検認用封印システムとして米国サンディア国立研究所が開発してきたものである。その検認方法は、封印取付時と査察時に記録した封印の光学パターンを目視比較するものであるが、この方法では査察官への負担が大きくなり、また主観的な判断となり得る場合もある。そこで、原研では簡単にしかも数値として客観的に検認結果の得られる電子式封印検認器の開発を行ってきた。これまで開発したモデルでは処理速度の制約から検認アルゴリズムは単純なものを用いているため、照射光量レベルの変化や検認器封印嵌合部のガタの影響を受けて検認精度が低下する弱点があった。今回開発した手法は、近年の演算プロセッサの処理速度の向上を考慮し画像処理技術を採用して上記弱点を克服し、検認精度を高めることができた。2台の試作機による検認試験の結果、本手法がコブラ封印の現場検認のために十分有効であることが確認できた。
石寺 孝充; 夏 暁彬; 出光 一哉*; 菊池 芳郎*
no journal, ,
腐食させた炭素鋼を圧縮ベントナイトに接触させ、ベントナイト中へ移行した鉄腐食生成物の存在形態を調べた。その結果、炭素鋼付近では非晶質の2価の水酸化物として、炭素鋼から離れるに従って3価の水酸化物として鉄腐食生成物は存在しているものと考えられた。
本多 充; 菊池 満; 安積 正史*
no journal, ,
The collisionality dependence of a shielding factor of a neutral beam driven current, which is generally neglected for most models currently used, is shown to be important especially for present-day tokamak experiments. An addition of friction coefficients involving beam ions to the Matrix Inversion method based on the moment approach readily makes it possible to estimate the collisionality-dependent shielding factor. The models proposed coincide with the collisionless model in the collisionless limit. They clearly elucidate the strong dependence of the shielding factor on collisionality, indicating that using a collisionless model always overestimates a beam driven current.
本多 充; 菊池 満; 安積 正史*
no journal, ,
The collisionality dependence of a shielding factor of a neutral beam driven current, which is generally neglected in most models currently used, is shown to be important especially for present-day tokamak experiments. An addition of friction coefficients involving beam ions to the Matrix Inversion method based on the moment approach readily makes it possible to estimate the collisionality-dependent shielding factor. The models proposed coincide with the collisionless model in the collisionless limit. They clearly elucidate the strong dependence of the shielding factor on collisionality, indicating that using a collisionless model always overestimates a beam driven current.
菊池 満; Fasoli, A.*; 滝塚 知典*; Diamond, P.*; Medvedev, S.*; Duan, X.*; 図子 秀樹*; 古川 勝*; 岸本 泰明*; Wu, Y.*; et al.
no journal, ,
トカマクにおける標準的なD型Hモードプラズマシナリオは熱粒子制御の観点からは課題を含んでいる。革新的なトカマク配位として負三角度の可能性が菊池等によって議論されている。CRPP-EPFLによる負三角度プラズマの実験と理論研究で閉じ込め改善が報告されており、負三角度配位はSOL流速の低減が示唆される。近年のタイプII ELMやグラッシーELMの理論研究によると第2安定化領域へのアクセスを閉じることと運動論的効果が小ELMの達成に重要であることがわかってきた。Medvedevによると負三角度では第2安定化領域への窓が閉じることが分かっている。講演では、これらを含む最近の理解進展をまとめる。
Francisco, P. C. M.; 松村 大樹; 菊池 亮佑*; 石寺 孝充; 舘 幸男
no journal, ,
The radionuclide Selenium-79 (Se-79) is predicted to be a key contributor to the long-term radiologic hazards associated with geological high-level waste (HLW) repositories. Se exists predominantly as selenide Se(-II) under anoxic conditions in the deep subsurface, and is likely immobilized via precipitation with, or adsorption on, Fe(II) minerals. However, the initial immobilization mechanisms with metastable Fe(II) minerals, and Se(-II)s subsequent response to iron phase transformation in the long term remain poorly understood. In this work, we investigated the retention and mobilization behavior of Se(-II) as a function of pH and the mode of its initial interaction with aqueous or solid Fe(II) phases. We carried out batch precipitation and transformation experiments under N atmosphere and reducing conditions. We examined two cases: in the first, Se(-II) was reacted with aqueous Fe(II), while in the second, Fe(OH) was first precipitated before reaction with Se(-II); both experiments were carried out at pH 8 and 12. In both cases, Se(-II) introduction resulted in the immediate precipitation of black particles. EXAFS and TEM characterization showed that Se(-II) precipitated as iron selenide nanoparticles in both cases regardless of pH. Aging of these initial precipitates at 
C resulted in magnetite crystallization. Regardless of whether Se(-II) was reacted with aqueous Fe(II) or solid phases, it was completely retained as discrete, crystalline FeSe at pH8. At pH12, Se(-II) was mostly remobilized; however, we observed evidence of partial retention via the precipitation of nanocrystalline iron selenide (FeSe
or Fe
Se
) on the surface of magnetite, as well as by incorporation in defects on the edges of magnetite crystals. These results show that pH controls long-term Se(-II) behavior and that magnetite crystallization may play a role in the retention of Se(-II), particularly at high pH.
Francisco, P. C. M.; 菊池 亮佑*; 松村 大樹; 塩飽 秀啓; 石寺 孝充; 舘 幸男
no journal, ,
Selenium-79 (Se-79) will be a significant contributor to the long-term radiologic hazards in geological repositories for high-level wastes due to its long half-life. Thus, understanding its behavior in anoxic and reducing subsurface environments prevalent in geological repositories is a key concern in repository safety assessments. There is limited information on primary reaction products arising from the interaction of aqueous Se species with either aqueous or solid Fe(II) phases, which are present in either as geological repositories as products of steel overpack corrosion or as accessory phases in buffer materials or host rocks. In this work, we investigated the interaction of aqueous Se(-II) and Se(IV), potentially the most mobile Se species in repositories, with aqueous Fe(II) and solid Fe(OH) at circumneutral and alkaline conditions, respectively. Using electron microscopy and XAFS spectroscopy, we identified beta-FeSe as the primary reaction product at circumneutral and alkaline conditions between Se(-II) and either aqueous Fe(II) and Fe(OH). For Se(IV), elemental Se(0) was the main reaction product at circumneutral conditions while iron selenides only became dominant at alkaline conditions; these results show rapid and efficient reduction of Se(IV). Aging the solids at 90C for 1 week induced the transformation of beta-FeSe and elemental Se(0) to FeSe at circumneutral conditions, while a proportion of Se was released back into solution at alkaline conditions. These results provide constraints on the initial behavior of Se upon release from the waste, and may be useful in validating long-term thermodynamic predictions. *This work was part of "The project for validating near-field assessment methodology in geological disposal (FY2021, Grant Number: JPJ007597)" supported by the Ministry of Economy, Trade and Industry of Japan.
Francisco, P. C. M.; 石寺 孝充; 塩飽 秀啓; 菊池 亮佑*; 舘 幸男
no journal, ,
As a long-lived fission product, Se-79 is predicted to account for a significant proportion of radioactivity long after the closure of a geological repository for high-level wastes. Predicting its behavior for long-term safety assessment of repositories thus requires a detailed understanding of its reactions with various geological repository components. Interaction with ferrous and sulfide aqueous species and solid phases could help attenuate Se concentrations under anoxic and reducing conditions in repositories. We performed four sets of coprecipitation experiments where Se(-II) was reacted with aqueous Fe(II) and with either monosulfides or polysulfides, at Fe/Stot ratios of 1 and 0.5. The precipitates were aged under anoxic conditions at ~25C for up to 5 months. The monosulfide coprecipitation experiments produced mackinawite and efficiently sequestered Se(-II) from solutions. XANES analyses showed that Se retained its -II oxidation state and EXAFS fitting results were consistent with Se being incorporated in the mackinawite lattice. Uptake was similarly efficient in the polysulfide experiments, though lesser Se was sequestered than in the monosulfide experiments. Unlike in the monosulfide experiments, Se was initially oxidized and precipitated as elemental Se(0). In the experiment at Fe/S 1, Se became incorporated in pyrite. Despite the very low abundance of pyrite, it was clear that it hosted most of the Se. In summary, monosulfide coprecipitation sequesters and retains Se in mackinawite, while reaction with polysulfides sequesters Se first as Se(0), then incorporates it in pyrite. Because sulfide speciation is tied to redox conditions, the results provide fundamental insights into the processes governing Se retention across a broad range of redox environments, which may aid in predicting Se migration behavior in geological repositories.
