Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
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.
高橋 嘉夫*; 山口 瑛子
no journal, ,
微量元素の化学種解析は、環境挙動の理解促進のために重要である。X線吸収端近傍構造(XANES)法は化学種解明に強力なツールであるが、目的元素の濃度が薄い場合、他元素からの干渉により測定が困難になる問題がある。この問題を克服するため、本研究では、エネルギー分散型及び波長分散型の新しいXANES測定法を実施した。特に波長分散型の手法を用い、粘土鉱物に吸着したバリウムとセシウムについて高分解能XANESを測定したところ、既存の手法では見分けるのが難しかった吸着サイトの違いや構造の違いが見分けられることが示唆された。