Innovative Disposal Container Materials: Improved Durability and Manufacturing Feasibility

Deep geological disposal of high-level radioactive waste (HLW) is the internationally preferred final waste management option to prevent the biosphere from radiologically relevant release of radioactive nuclides for at least 100,000 to 1 million years. Current repository concepts are based on a multi-barrier system consisting of geological, geo-technical and technical barriers as an engineered barrier system (EBS). Considered host rocks are e.g. crystalline rocks, claystone, or rock salt. In all cases disposal containers are a crucial technical barrier to safely enclose the HLW, either spent nuclear fuel (SNF) or vitrified high-level waste (VHLW) from reprocessing. Depending on the repository concept and the respective safety case disposal containers guarantee the safe confinement of their radioactive inventory not just during handling, emplacement, and potential retrieval but also during the post-closure phase of the repository for a certain period. Required container lifetimes usually vary between 1,000 and 100,000 years depending on the selected host rock and repository concept.

During container operation and their long-term disposal, they are subject to various mechanical, thermal, radiological, and geo-chemical/biological loads. Thus, mechanical stability and corrosion resistance in the long-term are among the most crucial challenges. Disposal container components lifetimes are typically calculated based on their time-dependent corrosion behaviour, with the implicit assumption that the design remains structurally stable for the required period.

Even though, the durability of several component materials subjected to corrosion processes have been previously studied in detail, the interaction of mechanical processes and corrosion calls for further study, and assessment of the impact of joint degradation modes on component lifetimes will result in a more robust and defensible safety case. Besides, as corrosion occurs in a thin interfacial surface layer between the component outermost surface and the environment, specific R&D work is required to understand the long-term performance controlled by the entire engineered barrier system (EBS) and to feed simulation and extrapolations tools by representative experimental data for validation.

Another approach to tackle the corrosion issue is to prevent and/or minimize it, thereby ensuring an even safer disposal. In this approach, materials much less prone to corrosion (e.g., copper, ceramic materials) can be used to fabricate the containers. Alternatively, protective coatings (e.g. copper coating) can be applied to current selected reference materials like steels. Both ways require validation of the materials durability under realistic, accelerated field conditions. 

The InCoManD work package 9 (Innovative and new Container/canister materials under disposal field conditions), part of the EURAD-2 European Partnership on Radioactive Waste Management (2024 – 2029), will address these issues through a collaborative project involving many countries across Europe (and beyond) with a shared goal. Building on the results of the ConCorD work package 15 (Container Corrosion under Disposal Conditions), part of the EURAD-1 programme (2019 - 2024), the InCoManD work package specifically aims to: (i) provide a better understanding of material degradation mechanisms, (ii) define optimised and innovative material solutions, (iii) develop comprehensive predictive models and common methodologies to enhance confidence in the results produced by each partner, and (iv) train new scientists in this field.