2019 Fiscal Year Final Research Report
Study on the solubility and structure of actinide hydroxides and oxides
| Project/Area Number |
16K18348
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| Research Category |
Grant-in-Aid for Young Scientists (B)
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| Allocation Type | Multi-year Fund |
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| Research Field |
Nuclear engineering
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| Research Institution | Kyoto University |
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Principal Investigator |
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| Project Period (FY) |
2016-04-01 – 2020-03-31
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| Keywords | 放射性廃棄物処分 / 4価金属イオン / 溶解度 / 構造解析 / 化学熱力学 / 粒子サイズ効果 |
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| Outline of Final Research Achievements |
Under the geochemical conditions of radioactive waste disposal, migration behaviors of radionuclides with tetravalent oxidation state are primarily controlled by the solubilities of their amorphous hydroxides. The present study revealed that the amorphous hydroxides consisted of oligomeric polynuclear hydrolysis species, primary particles with approximately 3 nm in size, and their aggregates larger than 100 nm from the combined measurements of X-ray adsorption spectroscopy, small angle X-ray scattering, and X-ray diffraction. The solubility of the amorphous hydroxides and crystalline oxides were investigated as functions of pH and temperatures to discuss the solubility behavior from the thermodynamic point of view. It was then suggested that the primary particle in the hierarchal structure of tetravalent hydroxides and oxides controlled the apparent solubility.
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| Free Research Field |
原子力学、放射性廃棄物処分、溶液化学、分析化学
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| Academic Significance and Societal Importance of the Research Achievements |
従来の4価金属イオンの水酸化物や酸化物に関する溶解度研究では、バルク結晶構造の同定が中心であったが、本研究では異なる分析手法を組み合わせることで幅広い空間スケールにおける固相の構造を調べた。溶解度制限固相としての1次粒子の存在を新たに提案するなど研究成果の学術的な意義は大きい。また、4価金属イオンとして振る舞う放射性核種の溶解挙動は、既存の放射性廃棄物のみならず、福島事故によって発生した燃料デブリの安定性評価においても重要であり、燃料デブリの処理処分という社会的な課題解決に向けた貢献も少なくないと考えられる。
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