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杉浦 佑樹; 石寺 孝充; 青柳 登; Mei, H.; 斉藤 拓巳*; 舘 幸男
no journal, ,
The sorption behavior of trivalent lanthanides (Eu/Sm) onto illite in the presence of dissolved inorganic carbon (DIC) was investigated by batch sorption experiments. The results of the experiments were interpreted using a thermodynamic sorption model (TSM). The TSM predicted that Eu/Sm forms clay mineral-Eu/Sm-carbonate surface ternary complexes. Time-resolved laser fluorescence spectroscopy (TRLFS) measurements were performed to obtain information on the chemical forms of Eu sorbed on illite. Parallel factor (PARAFAC) analysis of the TRLFS data indicated the presence of multiple chemical species. The pH dependence of the relative intensity of the chemical species derived from PARAFAC analysis was consistent with that of the surface species predicted by the TSM. The dominant chemical species in the presence of DIC was inferred to be coordinating carbonate ions based on the fluorescence lifetime. These results confirm the existence of surface ternary complex and the validity of the TSM.
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 ~25
C 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.
深津 勇太; Hu, Q.*; 舘 幸男
no journal, ,
Matrix diffusion and sorption are key processes to predict the transport of radionuclides in crystalline rocks for geological repository. Based on the previous studies, cationic sorption onto biotite would play an important role to evaluate the sorption and diffusivity of radionuclides in crystalline rock. In order to investigate the impact of sorption of cations in biotite on the diffusivity, in this study, we conducted through-diffusion tests of Cs
, Co
and Sr for several types of crystalline rocks, and compared the results in different concentrations of K that is one of the major cations of groundwater and also strong competitor for Cs sorption onto biotite. Moreover, the elemental maps of multiple tracers sorbed onto biotite of these rocks were directly obtained by using a laser ablation (LA)-ICP-MS, which provides microscale distribution of tracer elements within the rocks.
出井 俊太郎; 舘 幸男; 天野 由記; 杉浦 佑樹; Francisco, P. C. M.; 高橋 嘉夫*
no journal, ,
Se is one of the key radionuclides for safety assessment of the high-level radioactive waste (HLW) due to its long half-life and complex speciation depending on the redox condition. Since selenium is considered to be easily migrates as an anion, it is important to understand the retention mechanism of Se in the subsurface environment. The aim of this study is to elucidate the retention mechanisms of Se in the deep subsurface by clarifying the speciation of Se.
斉藤 拓巳*; 西 柊作*; 佐藤 颯人*; 宮川 和也
no journal, ,
高レベル放射性廃棄物処分において、地下水中の溶存有機物(DOM)は、放射性核種と錯生成することでその移行挙動を大きく変える。特に表層環境のDOMに対しては、金属イオンとの結合を多様な環境条件下で表すことのできるモデルが提案されている。そうしたモデルを地層処分の安全評価で使用するためには、深部地下環境のDOMと核種の結合反応を評価し、表層環境のDOMと比較することで、両者の類似点や相違点を理解することが必要である。本研究では、DOMの蛍光が金属イオンと結合することで消光されることに着目し、DOMを含む堆積岩系の深部地下水にユーロピウムを添加する消光実験を行い、得られた励起蛍光マトリクスに対して多変量解析法の一つであるParallel Factor Analysis(PARAFAC)を用いて、結合反応に寄与するDOMの蛍光成分を特定した。さらに、フーリエ変換イオンサイクロトロン共鳴質量分析から得られた高分解能の質量分布から結合反応に寄与するDOMの分子式を特定することで、その物理・化学的性質や起源、ユーロピウムとの反応性を議論した。
Mei, H.; 青柳 登; 斉藤 拓巳*; 杉浦 佑樹; 石寺 孝充; 田中 万也; 舘 幸男
no journal, ,
The sorption of U(VI) and trivalent lanthanides on illite at different pH and dissolved inorganic carbon (DIC) levels was investigated. The obvious inhibition effect of DIC on U(VI) and trivalent lanthanides sorption was revealed from the macroscopic batch experimental results. The formation of carbonate-containing sorption complexes was needed to be considered in the updated 2-site protolysis non-electrostatic surface complexation and cation exchange model to reproduce the experimental results. Based on the Parallel Factor Analysis analysis on the cryogenic time-resolved laser fluorescence spectroscopy spectra, the formation of ternary carbonate-containing sorption complexes was successfully identified. Identification of the sorption species adds more credibility to the predictive sorption model, which provides more confidence in the safety assessment of deep geological disposal.
土肥 輝美; 新里 忠史; 佐々木 祥人; 飯島 和毅
no journal, ,
Among the radionuclides emitted during the Fukushima Nuclear accident that took place on March 2011, 
Cs is the dominant one for exposure assessment due to both its large discharge amount and its relatively long half-life. Forests in the Fukushima prefecture account for around 70% of the land area and have been remained without decontamination, making radiocaesium migration in these ecosystems a particular concern. The JAEA has carried out research since the accident in order to clarify the transport behaviour of radiocaesum, particularly that from forests to the ocean via Fukushima river systems. Biomonitoring studies using lichens have also been conducted to investigate the characteristics of deposited radiocaesium. In this paper, the following themes are reviewed:(1) Radiocaesium behaviour in forests. (2) Modelling the behaviour of radiocaesium from forest to river and in their ecosystem. (3) Radiocaesium concentrations in wild mushrooms and plants, and mechanisms of radiocaesium accumulation in lichens.
田中 万也; 栗原 雄一*; 富田 純平; Maamoun, I.; 山崎 信哉*; 徳永 紘平; 福山 賢仁*; 香西 直文
no journal, ,
本研究では、人形峠環境技術センターの鉱さいたい積場において表層堆積物と水試料を採取してそれぞれ
Ra分析を行った。XRD分析から堆積物は主にフェリハイドライトやゲーサイトなどの鉄水酸化物からなることが分かった。堆積物のRa濃度は12,000から29,000Bq/kgで水中のRa濃度は60から580mBq/Lであった。結果として、堆積物と水との間の見かけの分配係数は3.1
10
から3.810
mL/gと見積もられた。これは、フェリハイドライトやゲーサイトに対して実験的に求められている分配係数よりも高い値であった。そのため、マンガン(IV)酸化物のようなラジウムを強く吸着するような鉱物が堆積物中に微量に含まれている可能性や下層堆積物からのラジウム供給により表層堆積物中のRa濃度が高まっている可能性がある。
) removal from aqueous solutions by mono-, bi-, and tri-metallic iron nanoparticles; A Comparative studyMaamoun, I.; 徳永 紘平; Falyouna, O.*; Eljamal, O.*; 田中 万也
no journal, ,
Recently, the rapid development of nuclear power technologies and the continuous energy demand around the world exhibited massive amounts of contaminated water with radionuclides. The exposure to TcVII-contaminated water can be harmful to human health, causing toxic effects and organs damage when ingested. Therefore, TcO removal from aqueous solutions can be challenging, in terms of fast and efficient immobilization. Correspondingly, perrhenate (ReO) was considered as perrhenate (TcO) surrogate to ease the radioactivity-related complications, owing to the physiochemical similarities between Tc and rhenium (Re). In this study, nickel (Ni) andzirconium (Zr) were considered in the preparation of bi- and tri-metallic Fe0 nanoparticles, as they both showed the highest ReO removal performance comparing with other metals. The effect of reaction conditions on ReO removal was investigated, including mass ratio of iron to the doped metal, material dosage, and initial pH. Results showed enhanced ReO removal rate when using bi-metallic Ni-Fe0 (mass ratio 2.5) and Zr/Fe0 (mass ratio 20) comparing with Fe0. The difference in ReO removal using mono-, bi-, and tri-metallic was not clear at high material dosage, such as 2.0 and 1.0 g/L. Nevertheless, comparing lower dosage (0.5 g/L)of bi- and tri-metallic to 1.0 g/L mono-metallic Fe0 dosage exhibited a clear superiority of tri-metallic Zr-Ni/Fe0 to other materials; where 0.5 g/L of the material could efficiently achieve around 98% ReO removal within just 10 min reaction time (1.8 times higher than 1.0 g/L Fe0). The significant enhancement in ReO removal rate by tri-metallic Fe0 nanoparticles can be attributed to the induced rate of electron transfer from iron core through the mixed Zr-Nideposits on Fe0 surface.
飯島 和毅
no journal, ,
福島第一原子力発電所(FDNPS)の廃炉の過程では、さまざまな放射性固体廃棄物が大量に発生する。それらの性質と量に関する大きな不確実性は、将来の廃棄物の処理および処分戦略を検討する際の大きな障害となる。本研究では、必要な廃棄物の特性を明確にし、廃棄物の流れ全体を最適化するために、廃棄物処分の安全性評価のアプローチを調査した。これまでの検討の結果、FDNPS廃棄物の場合、一般的な条件に不確実性が大きいため、保守的すぎる仮定は処分システムの要件が強すぎることにつながるため、参照ケースの評価は最も妥当な条件で実行される必要があると考えられた。次のステップとして、科学的根拠のある合理的な不確実性を考慮して、保守的なケースを定義する必要がある。