Articles techniques et présentations

Geological repository for highly radioactive waste disposal is a system of engineered and natural barriers. The objective of this system is to contain and isolate waste and protect the environment and humans from ionizing radiation. For the evaluation of performance of engineered barriers in the long-term perspective it is necessary to predict its behaviour once placed in the host rock as well as host rock response to the disturbances due to construction. Activities such as excavation and ventilation of waste disposal tunnel of initially saturated porous media, the processes such as gas generation due to corrosion of waste package may also result in de-saturation of barriers. In this study the analysis of repository barriers (backfill, concrete, inner excavation disturbed zone (EDZ), outer EDZ, host rock) hydraulic evolution and the scope of gas induced de-saturation was analysed with COMSOL Multiphysics®. This requires modelling of two-phase flow of miscible fluid (water and H2) considering important phenomena such as gas dissolution and diffusion, advective-diffusive transport in gaseous phase. Evolution of material permeability and water retention need to be consistent with each other and based on the same measurement dataset. For this purpose, a mass balance equations for each fluid were solved with Coefficient PDE interface of COMSOL Multiphysics®. Modified Van Genuchten/Mualem model (VGM/Pe model) with representation of gas entry pressure as presented in Amri et al. (2022) was implemented too. Preliminary results of numerical analysis showed the desaturation of excavation disturbed zone (EDZ) and host rock to some extent due to ventilation of 50 years. H2 gas injection led to desaturation of engineered barriers and part of EDZ close to gas generation place vanishing soon after finish of gas generation, while host rock remained saturated during gas injection phase (50-100 000 years). Analysis of these processes is a part of LEI activities in EC programme EURAD Work package GAS (Grant Number 847593).