How mobile is tritiated water through unsaturated cement-based materials? New insights from two complementary approaches

Abstract

This work presents a novel approach to study tritiated water (HTO) diffusion through unsaturated cement-based materials (hardened CEM V/A cement pastes). The diffusion studies were performed under hydric conditions covering those that can prevail in near-surface disposal facilities for short-lived nuclear waste. In order to investigate the required large range of suction, two complementary techniques were developed. The first technique was based on a through-diffusion method where suction (up to 9 MPa) was controlled using osmosis process. In the second technique diffusion experiments were performed in humidity chambers controlled by under-saturated saline solutions (suction up to 170 MPa). Tritiated water (HTO) was added in the saline solution and diffused through the studied material in gas form. This latter method showed that the extent of irreversible HTO uptake on cement-based materials increased with desaturation. Moreover, diffusive data acquired by means of the two techniques revealed a decrease of effective diffusion coefficient by a factor of 10 from 100% to 23% of saturation degree. Comparison with dihydrogen (HT) diffusion results suggests that HTO diffuses through unsaturated cement-based materials at rates more than 4 orders of magnitude lower.

Influence of Water Saturation Level on Electrical Double Layer Properties in a Clay Mineral Mesopore: A Molecular Dynamics Study

“…Diffusion experiments have shown that anion diffusion is more strongly reduced than cation diffusion in the presence of water unsaturated conditions. Numerous processes were put forward to explain this observation, including differences in diffusion pathway disruptions among cations, anions, and neutral molecules. − Our study emphasizes that mechanisms taking place at the surface, such as formation and immobilization of ion pairs, may also be partly responsible for the observed differences between anion and cation diffusion property evolution with desaturation. As for water diffusion, our study corroborates the fact that a limited desaturation is not responsible for a decrease of water molecules self-diffusion coefficient.…”

Water and ion diffusion in partially-water saturated compacted kaolinite: Role played by vapor-phase diffusion in water mobility

“…This exchange is assumed to be instantaneous, reversible and without significant fractionation between the different isotopes of the water molecules, as demonstrated by Savoye et al (2018) for HTO.…”

Performance Prediction and Mix Ratio Optimization for Multielement Green High-Performance Fiber-Reinforced Cement Matrix Composite

“…Similar to seismic performance and fire resistance, the dynamic mechanical properties are an important indicator of the macro performance of green cement matrix composite structures [18][19][20][21][22]. Tran et al [23] investigated the dynamic mechanical properties of two typical green composites, i.e., cement matrix regeneration composite and alkaline-activated material, studied how the graphene oxide content enhances the macro dynamic mechanical properties of cement matrix regeneration composite, analyzed the influence of different renewable rubber replacement ratios on the fluidity and static mechanical properties of alkaline-activated material, and evaluated the ecological and economic performance of the materials through mix ratio optimization.…”