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Battulga, B.; 中西 貴宏; 安藤 麻里子; 小嵐 淳
no journal, ,
水環境におけるプラスチックは科学的に大きく注目されているが、プラスチックに含まれる放射性物質やプラスチック上の有機付着物の動態はほとんど知られていない。本研究では、日本の対照的な2つの沿岸域で採取したプラスチック上の有機付着物と堆積物に対して、その特性や環境中の放射性物質、特に放射性セシウム(
Cs)との相互作用を明らかにすることを目的としている。また、有機付着物と堆積物試料の安定同位体(
Cと
N)の季節変動を解析した。研究の結果、放射能濃度が292
19.4 Bq kg
有機付着物(dw)の微量のCsが有機付着物内で検出され、これは1.150.08 Bq kgプラスチック(dw)に相当する。
松枝 誠; 青木 譲; 小荒井 一真; 寺島 元基; 高貝 慶隆*
no journal, ,
長半減期の
Iは、原子力施設から放出される放射性同位元素の環境動態を推定するためのトレーサーとして重要な情報を我々に提供してきた。誘導結合プラズマ質量分析法(ICP-MS)は、迅速なデータ取得が可能だが、m/z129の主要な干渉物質(
IH
とXe)により、適用範囲が制限されている。今まで、XeはOガスをICP-MS内の反応セルに導入することで除去可能であることが報告されている。また、タンデム質量分析(ICP-MS/MS)により、IHの生成を抑制できるようになった。しかし、様々な環境試料への適用には、より精密な干渉物の除去が必要となる。本研究では、ICP-MS/MS内の反応セルにおける干渉物質とIの気相反応について検討した。その結果、O-CO混合ガスを反応セルに導入することで、m/z129のバックグラウンドカウントを最小レベルまで低減した。
山口 瑛子; 奥村 雅彦; 高橋 嘉夫*
no journal, ,
粘土鉱物は地球表層に広く存在し多くの陽イオンを吸着することから、様々な元素の環境挙動を支配している。粘土鉱物に吸着したイオンの吸脱着挙動は分子レベルの吸着構造によって異なるため、分子レベルの情報に基づいた包括的な理解が必要である。そこで本研究では、特に重要な元素であるラジウムを含む多くのイオンについて、系統的な広域X線吸収微細構造(EXAFS)測定と第一原理計算を実施し、元素間の比較を行った。これらの結果から、粘土鉱物への吸着構造は、水和のエネルギーと粘土鉱物への親和性のバランスで決定しており、水和エンタルピーとイオン半径が指標として有用であることが分かった。
Wang, Q. M.*; Hu, Q.*; Zhao, C.*; Zhang, T.*; 深津 勇太; 舘 幸男
no journal, ,
Fluid flow and chemical transport in porous media are the macroscopic consequences of pore structure, which integrates geometry (e.g., pore size and surface area, pore-size distribution) and topology (e.g., pore connectivity). Low-permeability geological media whose pores are poorly interconnected will exhibit the characteristics of anomalous diffusion and sample size-dependent effective porosity, which will strongly impact long-term net diffusion and retention of radionuclides in geological repository settings. A suite of experimental approaches is utilized to study the microscopic pore structure and macroscopic fluid flow and chemical transport for a range of natural rocks (such as clay/shale, crystalline rock, salt), in addition to clay minerals. With a particular focus on quantifying the presence and magnitude of isolated pores for a reduced effective porosity in low-permeability geomedia, the integrated methodologies for basic properties and pore structure characterization include X-ray diffraction, thin section petrography, grain size distribution, water immersion porosimetry, mercury intrusion porosimetry, nitrogen physisorption, scanning electron microscopy, X-ray computed tomography, and (ultra-)small angle neutron (or X-ray) scattering. In addition, custom-designed gas diffusion, tracer recipe involving a range of anionic and cationic chemicals with subsequent analyses by laser ablation and inductively coupled plasma-mass spectrometry, along with batch sorption, column transport, and imbibition tests were conducted for coupled effects of pore structure and chemical retention/transport.
寺島 元基; 田籠 久也*; 渡辺 勇輔; 佐々木 祥人
no journal, ,
Elution of radiocesium (Cs) from litter and its humus in Cs-contaminated forest can be a key process determining a discharge of Cs from forests into rivers around the Fukushima Dai-ichi Nuclear Power Station (FDNPS). Quantitative understanding of this process is then necessary for predicting the contamination situation in the future. However, chemical equilibrium modelling of Cs in the elution has not been addressed. The influence of solution conditions such as pH, coexisting cations, and dissolved organic matter (DOM) on the elution is still unclear. In this study, degree of the elution of Cs from litter (i.e., fallen leaves) or its humus in the contaminated forest near the FDNPS was evaluated by a batch method and was then compared with those from the calculation with NICA-Donnan model, assuming a ternary system of Cs, DOM, and solid organic matter (SOM).
奥村 雅彦; 小林 恵太; 山口 瑛子
no journal, ,
粘土鉱物の研究において、数値シミュレーション、特に分子動力学(MD)は重要な研究手法である。古典分子動力学法(CMD)と第一原理分子動力学法(AIMD)がよく使われており、CMDは精度が劣るが計算効率が良いため大規模なシミュレーションに適している一方、AIMDは精度が高いが計算コストが高いが精密な評価が可能である。機械学習分子動力学法(MLMD)は、第一原理計算の結果を学習させた人工ニューラルネットワークを利用することで、低い計算コストと高い精度を両立している。超水和カオリナイトは、層間に薄い水層を示す粘土鉱物であり、高圧下における極限の鉱物-流体界面の物理/化学を知るために魅力的な粘土鉱物である。本発表では、超水和カオリナイトの水酸基の振動、層間での水の拡散などの静的・動的特性について、我々のMLMDシミュレーションの結果を紹介する。
, SeO
, and SeO
-coprecipitated barite after treatment with phosphate ions徳永 紘平; 田中 万也; 高橋 嘉夫*; 香西 直文
no journal, ,
This study systematically investigated the stability of iodate (IO), selenite (SeO), and selenate (SeO) coprecipitation with barite. Iodine-129 and selenium-79 are long half-life fission products of uranium-235 and mainly exist as oxyanions in liquid nuclear wastes, and these oxyanions are highly soluble in water and thus mobile in the geological environment. Our results showed that these oxyanions were gradually released into ultrapure water with time. Leaching of the oxyanions significantly increased in leaching solutions containing NaCl, NaNO, and NaSO. Conversely, leaching of the oxyanions was suppressed in KHPO solution, indicating that phosphate stabilized the oxyanion-bearing barite. The effect of phosphate treatment on oxyanion-bearing barite was further investigated. The results showed that the barite surface was modified with phosphate, and a thin surface layer of a barium phosphate-like structure was formed. Hence, a considerable improvement in the stability of iodate, selenite, and selenate coprecipitated with barite can be achieved using phosphate as a stabilizing reagent. Therefore, the barite coprecipitation combined with subsequent phosphate treatment may be a promising method to efficiently remove radioactive iodate, selenite, and selenate from wastewater and stabilize them as barite coprecipitates. To the best of our knowledge, this is the first study to demonstrate the effect of phosphate on the stabilization of the barite surface structure and its application for the development of geological repositories.
渡辺 勇輔; 寺島 元基; 松枝 誠; 小荒井 一真; 青木 譲; 井上 準也
no journal, ,
In the safety assessment of radioactive waste disposal, understanding the migration behaviour of radionuclides near the surface environment is important for assessing exposure in the biosphere. After radionuclides migrate from the subsurface to the biosphere via groundwater to aquatic environments such as well water and river water, their concentrations are controlled by dilution by surface water and adsorption to soil and sediments. A more realistic assessment of the amount of radionuclides emerging to the surface and their subsequent mobility and bio-transferability requires an understanding of the processes that groundwater may be subjected to immediately after emerging to the surface. At Ningyo-toge Environmental Engineering Center, JAEA in Okayama Prefecture, heavy metals such as U and As are leached by groundwater from a sedimentation site where residues after U extraction from uranium ore are disposed, and JAEA manages the quality of these waters and discharges them into an off-site river. The groundwater immediately after passing through the sedimentation site is considered to contain high concentrations of divalent iron, but during a certain period of storage iron oxidation forms iron hydroxide minerals, which are deposited in the mill tailing pond. In this study, this anoxic groundwater and the water that subsequently migrated to the mill tailing pond and in situ sediments were sampled to investigate the trace element compositions and mineral compositions of the sediments. The results showed that trace elements such as REEs, As and U in the groundwater after the upwelling decreased with change of redox condition of water. Geochemical modeling based on these results showed that changes in the concentrations of these elements can be explained by adsorption reactions on iron hydroxide produced by the oxidation of divalent iron present in groundwater.