Gas Flow through Unsaturated Scaled Barrier for the Disposal of High-Level Nuclear Waste

The safe and permanent disposal of high-level nuclear waste (HLW) is an unresolved problem in the nuclear industry. It is therefore imperative to find a solution for this relevant and timely problem. Previous studies are focused on the determination of the clay-barrier gas breakthrough pressure in the field and laboratory testing to determine the safety of the Engineered Barrier System. Most of these experiments are conducted in one-dimensional oedometric cell in which the saturated bentonite sample is enclosed in a stainless-steel container. Hence, a need was felt to conduct experiments which are more representative of the field conditions to which the barrier material (MX-80 clay in this paper) is exposed to in deep geological repository. Therefore, attention is given to gas flow through the interface as this flow through the dissimilar interface is not fully understood yet. These interfaces may offer a preferential pathway for the release of gas from the HLW to the host rock and hence the environment. This paper studies gas breakthrough mechanisms through the rock-clay contact under controlled thermo-hydro-mechanical (THM) conditions in the laboratory using a new and advanced THM multipurpose cell specifically developed to study this phenomenon in collaboration with UPC Barcelona. The paper discusses the time-dependent breakthrough pressure test through a rock barrier prototype and concludes that the rock-barrier interface plays a critical role in determining the overall efficiency of the Engineered Barrier System (EBS) and can allow the gas outflow at a lower breakthrough pressure. Hence, it is important to understand the mechanism involved in the breakthrough of gas through the interface of dissimilar material in EBS.