報告書番号

N11017

タイトル（和文）

自然電位探査法による岩盤の酸化還元状態評価法の提案

タイトル（英文）

Development of an investigation method for redox condition of rocks by self potential (SP) method

概要 （図表や脚注は「報告書全文」に掲載しております）

本研究では、日本原燃(株)敷地内の試験空洞における酸化還元境界の周辺を対象に自然電位探査を実施し、酸化還元境界における自然電位の変化特性を把握するとともに、水質や岩石のゼータ電位との比較を行うことで、酸化還元境界を自然電位探査により把握できる可能性について評価を行った。その結果、酸化還元境界を境に自然電位が大きく変化していることが明らかになった。そして、自然電位の変化にはpH、ゼータ電位などといった酸化還元環境が重要な役割を担っていることが示された。以上より、酸化還元環境を把握する手法として、自然電位探査が適用できる可能性が示された。また、同じ箇所においてpHを測定し、両者のデータを比較することで、より詳細に評価できることが示された。

概要 （英文）

One of the major issues in subsurface disposal of low level radioactive wastes is that long term behaviors of sedimentary rocks can be affected by geochemical factors. Redox conditions can affect to corrosion of metal included in artificial barrier or wastes and adsorption characteristics of a nuclide. Therefore, it is necessary to develop a method for evaluating the redox conditions around natural barrier at waste facilities.
In general, geochemical properties are acquired by rock samples or water sampling at a borehole. However, there is a possibility not to acquire data we want to evaluate. If geophysical methods are applied, redox conditions can be evaluated widely and briefly. There is a possibility that self potential (SP) and redox conditions have a correlation. So we have conducted self potential method around test caverns where redox front can be observed at the Rokkasho site.
The results demonstrated that self potential decreased around redox front. There was a positive correlation between self potential and pH. One of the factors of self potential change is difference of elevation, however, self potential change around redox front was larger than that expected from elevation difference. Zeta potential is one of the important factors for determination of self potential, and it had a correlation with self potential or pH. Therefore, there is a possibility that self potential change occurs by geochemical condition changes around redox front, and redox condition can be detected by self potential method.

報告者

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