Diffusive Transport of Dissolved Gases in Potential Concretes for Nuclear Waste Disposal

Elke Jacops,Lander Frederickx,Quoc Tri Phung,Séverine Levasseur

doi:10.3390/su131810007

Abstract

In many countries, the preferred option for the long-term management of high- and intermediate level radioactive waste and spent fuel is final disposal in a geological repository. In this geological repository, the generation of gas will be unavoidable. In order to make a correct balance between gas generation and dissipation by diffusion, knowledge of the diffusion coefficients of gases in the host rock and the engineered barriers is essential. Currently, diffusion coefficients for the Boom Clay, a potential Belgian host rock, are available, but the diffusion coefficients for gases in the engineered concrete barriers are still lacking. Therefore, diffusion experiments with dissolved gases were performed on two concrete-based barrier materials considered in the current Belgian disposal concept, by using the double through-diffusion technique for dissolved gases, which was developed in 2008 by SCK CEN. Diffusion measurements were performed with four gases including helium, neon, methane and ethane. Information on the microstructure of the materials (e.g., pore size distribution) was obtained by combining N2-adsorption, mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and water sorptivity measurements. A comparison was made with data obtained from cement-based samples (intact and degraded), and the validity of existing predictive models was investigated.

Highlights

The preferred option adopted by many countries for the long-term management of high- and intermediate-level radioactive waste and/or spent fuel is its disposal in a geological repository, in which a multi-barrier system, combining natural host rock and engineered barriers, is adopted
In a plastic clay such as the Boom Clay, the use of concrete is difficult to avoid, and cement-based materials will be an essential part of the engineered barrier system (EBS) (Figure 1)
The specific surface area (SSA) obtained by the Brunauer–Emmett–Teller (BET) and t-plot methods are threefold for the supercontainer compared to the ones of lining concrete

Summary

Introduction

The preferred option adopted by many countries for the long-term management of high- and intermediate-level radioactive waste and/or spent fuel is its disposal in a geological repository, in which a multi-barrier system, combining natural host rock and engineered barriers, is adopted. In Belgium, no formal decision on a host formation has been taken yet, but for R&D purposes, the Belgian radioactive waste management organization ONDRAF/NIRAS considers Boom Clay as one of the potential natural barriers for a geological disposal facility in poorly indurated plastic clays. The three main cement-based components which can be distinguished in this “supercontainer concept” are: the disposal supercontainer, the backfill and the gallery lining. The supercontainer is a very large concrete container which will contain certain types of waste. These supercontainers will be placed in the disposal galleries. The most important role of cement-based backfill is to help create beneficial conditions for the integrity of the waste package (steel corrosion) because of its high pH buffering capacity for a very long period

Methods

Results

Conclusion