Professor Masaharu Tanimizu, Department of Applied Chemistry for Environment, has been conducting researches on the estimation of the origin of terrestrial water and environmental changes using high-precision isotopic indicators of elements. Here as a result of his research, which aimed to understand the chemical behavior of uranium in reductive deep groundwater by using an analytical method to rapidly and precisely measure the isotopic ratio of uranium dissolved in ultra trace amounts in groundwater, were published in the Geochemical Journal in February 2025. The study found that the 234U/238U ratio, the abundance ratio of both 234U and 238U long half-life radionuclides, is very large in reducing deep groundwater compared to shallow oxidizing groundwater, along with a decrease in uranium dissolved content. This deviation from equilibrium in radiogenic decay implies that the groundwater environment has been significantly disturbed in times younger than the past million years, pointing to the possibility of glacial recharge of natural water and mixing with deep groundwater. These findings on the chemical behavior of uranium in groundwater are related to the long-term stability of the groundwater environment, and are expected to contribute to future studies of geological disposal.

 

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Journal Name: Geochemical Journal
Article title: Large disequilibrium of 234U/238U isotope ratios in deep groundwater and its potential application as a groundwater mixing indicator
Authors: Chika Kuribayashi, Kazuya Miyakawa, Akane Ito, and Masaharu Tanimizu
DOI: https://doi.org/10.2343/geochemj.GJ24028