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論文

Structural and compositional characteristics of Fukushima release particulate material from Units 1 and 3 elucidates release mechanisms, accident chronology and future decommissioning strategy

Martin, P. G.*; Jones, C. P.*; Bartlett, S.*; Ignatyev, K.*; Megson-Smith, D.*; 佐藤 志彦; Cipiccia, S.*; Batey, D. J.*; Rau, C.*; 末木 啓介*; et al.

Scientific Reports (Internet), 10, p.22056_1 - 22056_17, 2020/12

 被引用回数:0 パーセンタイル:0.01(Multidisciplinary Sciences)

The structural form and elemental distribution of material originating from different Fukushima Daiichi Nuclear Power Plant reactors (Units 1 and 3) is hereby examined to elucidate their contrasting release dynamics and the current in-reactor conditions to influence future decommissioning challenges. Complimentary computed X-ray absorption tomography and X-ray fluorescence data show that the two suites of Si-based material sourced from the different reactor Units have contrasting internal structure and compositional distribution. The known event and condition chronology correlate with the observed internal and external structures of the particulates examined, which suggest that Unit 1 ejecta material sustained a greater degree of melting than that likely derived from reactor Unit 3. In particular, we attribute the near-spherical shape of Unit 1 ejecta and their internal voids to there being sufficient time for surface tension to round these objects before the hot (and so relatively low viscosity) silicate melt cooled to form glass. In contrast, a more complex internal form associated with the sub-mm particulates invoked to originate from Unit 3 suggest a lower peak temperature, over a longer duration. Using volcanic analogues, we consider the structural form of this material and how it relates to its environmental particulate stability and the bulk removal of residual materials from the damaged reactors. We conclude that the brittle and angular Unit 3 particulate are more susceptible to further fragmentation and particulate generation hazard than the round, higher-strength, more homogenous Unit 1 material.

論文

Project IPAD; A Database to catalogue the analysis of Fukushima Daiichi accident fragmental release material

Martin, P.*; Alhaddad, O.*; Verbelen, Y.*; 佐藤 志彦; 五十嵐 康人*; Scott, T. B.*

Scientific Data (Internet), 7, p.282_1 - 282_8, 2020/08

 被引用回数:0 パーセンタイル:0.91(Multidisciplinary Sciences)

The 2011 accident at Japan's Fukushima Daiichi Nuclear Power Plant released a considerable inventory of radioactive material into the local and global environments. While the vast majority of this contamination was in the form of gaseous and aerosol species, of which a large component was distributed out over the neighbouring Pacific Ocean (where is was subsequently deposited), a substantial portion of the radioactive release was in particulate form and was deposited across Fukushima Prefecture. To provide an underpinning understanding of the dynamics of this catastrophic accident, alongside assisting in the off-site remediation and eventual reactor decommissioning activities, the "International Particle Analysis Database", or "IPAD", was established to serve as an interactive repository for the continually expanding analysis dataset of the sub-mm ejecta particulate. In addition to a fully interrogatable database of analysis results for registered users (exploiting multiple search methods), the database also comprises an open-access front-end for members of the public to engage with the multi-national analysis activities by exploring a streamlined version of the data.

論文

Assessment of the mode of occurrence and radiological impact of radionuclides in Nigerian coal and resultant post-combustion coal ash using scanning electron microscopy and gamma-ray spectroscopy

Okeme, I. C.*; Scott, T. B.*; Martin, P. G.*; 佐藤 志彦; Ojonimi, T. I.*; Olaluwoye, M. O.*

Minerals (Internet), 10(3), p.241_1 - 241_15, 2020/03

 被引用回数:2 パーセンタイル:58.39(Geochemistry & Geophysics)

Natural radionuclide concentrations in coal and associated fly ash can occur at levels well in excess of those observed in other materials; enough to raise potential human and environmental health concerns when (re)suspended or incorporated into construction materials. To evaluate such concerns, this study characterised coal and fly ash samples obtained from two Nigerian coal mines (Okaba and Omelewu) using high resolution gamma spectroscopy combined with scanning electron microscopy and energy dispersive spectroscopy. Discrete uraninite particles were observed dispersed within the fly ash samples, alongside U and Th containing mineral grains (monazite, xenotime and zircon) with monazite the most abundant radioactive mineral particles. The pitted and cracked surface morphologies of these radioactive particles (with sizes between 10$$mu$$m and 80$$mu$$m) indicates their susceptibility for disintegration into more dangerous and readily inhalable PM2.5 aerosol particles, with the potential to deliver localised dose and cause chronic respiratory diseases. While the results of activity concentrations and radiological hazard indices (radium equivalent, annual effective dose equivalent, total radium, and excess lifetime cancer risk) from Okaba and Omelewu coal samples were of no concern, results for the corresponding fly ash samples from both mines were between 3 and 5 times higher than internationally recommended safe limits. These results therefore imply that such coal-derived fly ash is not safe for incorporation in the construction of residential houses and should be properly disposed of or contained to prevent hazard due to increased risk of prolonged indoor exposure to gamma radiation, radon gas and inhalation of liberated radioactive particles.

論文

Compositional and structural analysis of Fukushima-derived particulates using high-resolution X-ray imaging and synchrotron characterisation techniques

Martin, P. G.*; Jones, C. P.*; Cipiccia, S.*; Batey, D. J.*; Hallam, K. R.*; 佐藤 志彦; Griffiths, I.*; Rau, C.*; Richards, D. A.*; 末木 啓介*; et al.

Scientific Reports (Internet), 10(1), p.1636_1 - 1636_11, 2020/01

 被引用回数:4 パーセンタイル:62.5(Multidisciplinary Sciences)

Both the three-dimensional internal structure and elemental distribution of near-field radioactive fallout particulate material released during the March 2011 accident at the Fukushima Daiichi Nuclear Power Plant is analysed using combined high-resolution laboratory and synchrotron radiation X-ray techniques. Results from this study allow for the proposition of the likely formation mechanism of the particles, as well as the potential risks associated with their existence in the environment, and the likely implications for future planned reactor decommissioning. A suite of particles is analyzed from a locality 2 km from the north-western perimeter of the site north of the primary contaminant plume in an area formerly attributed to being contaminated by fallout from reactor Unit 1. The particles are shown to exhibit significant structural similarities; being amorphous with a textured exterior, and containing inclusions of contrasting compositions, as well as an extensive internal void volume bimodal in its size distribution. A heterogeneous distribution of the various elemental constituents is observed inside a representative particle, which also exhibited a Fukushima-derived radiocesium ($$^{134}$$Cs, $$^{135}$$Cs and $$^{137}$$Cs) signature with negligible natural Cs. We consider the structure and composition of the particle to suggest it formed from materials associated with the reactor Unit 1 building explosion, with debris fragments embedded into the particles surface. Such a high void ratio, comparable to geological pumice, suggests such material formed during a rapid depressurisation and is potentially susceptible to fragmentation through attrition.

論文

Impact of stellar superflares on planetary habitability

山敷 庸亮*; 前原 裕之*; Airapetian, V.*; 野津 湧太*; 佐藤 達彦; 野津 翔太*; 黒木 龍介*; 村嶋 慶哉*; 佐藤 啓明*; 行方 宏介*; et al.

Astrophysical Journal, 881(2), p.114_1 - 114_24, 2019/08

 被引用回数:14 パーセンタイル:80.03(Astronomy & Astrophysics)

系外惑星における生命存在の可能性を検討する際、恒星が引き起こすスーパーフレアによる影響を評価することは重要となる。そこで本研究では、いくつか実在する恒星と仮想的な惑星を想定し、その大気・海洋内における被ばく線量を様々なタイプの太陽フレアに対して推定する方法を提案する。具体的には、粒子・重イオン輸送計算コードPHITSと系外惑星データベースシステムExoKyotoを組み合わせ、実際に観測された太陽フレアと恒星フレアの比較から影響を推定する。その結果、ある程度の大気圧があれば、惑星地表面における被ばく線量は複雑系生物の致死量には至らない可能性が高いことが分かった。

論文

Provenance of uranium particulate contained within Fukushima Daiichi Nuclear Power Plant Unit 1 ejecta material

Martin, P. G.*; Louvel, M.*; Cipiccia, S.*; Jones, C. P.*; Batey, D. J.*; Hallam, K. R.*; Yang, I. A. X.*; 佐藤 志彦; Rau, C.*; Mosselmans, J. F. W.*; et al.

Nature Communications (Internet), 10(1), p.2801_1 - 2801_7, 2019/06

 被引用回数:15 パーセンタイル:84.77(Multidisciplinary Sciences)

二次イオン質量分析(SIMS)測定とシンクロトロン放射(SR)分析技術を福島第一原子力発電所(FDNPP)の1号機原子炉由来のサブミリメートル粒状物質に対して分析を行った。これらの方法によりより大きなSiベースの放出物に含まれるミクロンスケールのU微粒子の分布、状態および同位体組成を調査することが可能であった。SRマイクロフォーカスX線蛍光(SR-micro-XRF)と吸収コントラストSRマイクロフォーカスX線トモグラフィー(SR-micro-XRT)を組み合わせることにより、U微粒子は粒子の外周の周りに位置することがわかった。高多孔質粒子これらの捕捉された粒子のいくつかのシンクロトロン放射マイクロフォーカスX線吸収端近傍構造(SR-micro-XANES)分析により、U(IV)酸化状態で存在することを明らかにした。このUが原発由来であることの確認は、FDNPPの1号機からの出所に特徴的な同位体濃縮比を有する二次イオン質量分析(SIMS)分析によって検証された。これらの結果は、使用済み燃料放出物が存在するという事象シナリオ(炉心1号機からある程度の炉心細分化および放出が起こったこと)の明確な証拠である。このUが環境や健康への危害を表す可能性は低いと予想されるが、将来的に母材であるSi含有バルク粒子の分解が生じると推定される。

論文

Gyrokinetic studies of turbulence, equilibrium, and flows in the tokamak edge

Scott, B. D.*; Da Silva, F.*; Kendl, A.*; 宮戸 直亮; Ribeiro, T.*

Proceedings of 23rd IAEA Fusion Energy Conference (FEC 2010) (CD-ROM), 8 Pages, 2011/03

ジャイロ運動論に基づくトカマク端乱流の理論及びシミュレーションの進展について報告する。強いE$$times$$B流の存在する場合のジャイロ運動論的ラグランジアンの新しい定式化を構築した。それは従来から用いられてきた形式及び簡約化MHDモデルと対応づけが可能である。粒子,運動量,エネルギー及びエントロピーの保存が理論的に示され、シミュレーションにおいても確認された。新古典輸送及びMHD平衡が分布関数全体(total-f)を電磁的に解くシミュレーションモデルFEFIを用いて再現された。摂動分布関数(delta-f)によるジャイロ運動論的周辺乱流シミュレーションを局所的な磁束チューブモデルdelta-FEFIを用いて各磁気面で行い、プラズマ端-炉心の境界領域における結果を示す。また、現在進行中のELM崩壊シナリオのジャイロ流体における研究も報告する。ペデスタル部におけるブートストラップ電流が不安定モード・乱流にどのような影響を与えるかを考察する。

論文

Global nonlinear electromagnetic simulations of tokamak turbulence

Bottino, A.*; Scott, B. D.*; Brunner, S.*; McMillan, B. F.*; Tran, T. M.*; Vernay, T.*; Villard, L.*; Jolliet, S.; Hatzky, R.*; Peeters, A. G.*

IEEE Transactions on Plasma Science, 38(9), p.2129 - 2135, 2010/09

 被引用回数:24 パーセンタイル:71.36(Physics, Fluids & Plasmas)

The particle-in-cell code ORB5 is a global gyrokinetic turbulence simulation code in tokamak geometry. It solves the gyrokinetic equation in the whole plasma core, including the magnetic axis. A field-aligned filtering procedure and sophisticated noise/control and heating operators allow for accurate simulations. Recently, the code ORB5 has been extended to include self-consistent perpendicular magnetic field perturbations. The inclusion of magnetic perturbations allows for a comprehensive study of finite $$beta$$ effects on microinstability. In this paper, we present the first linear and nonlinear code results concerning electromagnetic effects on tokamak microinstabilities.

論文

Spectroscopy of $$^{257}$$Rf

Qian, J.*; Heinz, A.*; Khoo, T. L.*; Janssens, R. V. F.*; Peterson, D.*; Seweryniak, D.*; Ahmad, I.*; 浅井 雅人; Back, B. B.*; Carpenter, M. P.*; et al.

Physical Review C, 79(6), p.064319_1 - 064319_13, 2009/06

 被引用回数:28 パーセンタイル:83.93(Physics, Nuclear)

アルゴンヌ国立研究所の反跳核分離装置を用いて、$$^{257}$$Rfの$$alpha$$線,$$gamma$$線,内部転換電子測定実験を行った。$$^{257}$$Rfの励起状態に、高いK量子数を持った3準粒子状態と解釈される半減期160$$mu$$秒の新核異性体を発見した。また、$$alpha$$崩壊の抑止係数より、$$^{257}$$Rfの娘核である$$^{253}$$Noの1準粒子状態の中性子軌道配位を同定した。中性子数151核の1/2$$^{+}$$[620]準位の励起エネルギーの系統性より、中性子数152の変形閉殻の大きさが、原子番号が増えるにつれて大きくなることを明らかにした。

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