Feasibility of Backfilling and Sealing Measures: Findings from the VerfüllEND Project
Event banner for the 5th Tage der Standortauswahl, held on 23–24 April 2026 in Leipzig.
The 5th Tage der Standortauswahl took place in Leipzig from 23 to 24 April 2026. BGE TECHNOLOGY GmbH (BGE TEC) presented findings from the research project "Feasibility Assessment of Backfilling and Sealing Measures for a High-Level Radioactive Waste Repository" (VerfüllEND). The project addressed whether the international state of science and technology on backfilling and sealing measures is sufficient to backfill and seal a high-level radioactive waste repository in Germany across the full range of geological conditions covered by the site selection procedure.
Research Questions and Approach
A Technology Readiness Level (TRL) of at least 3 was used as assessment criterion; this corresponds to demonstrating that a technology is fundamentally functional. Using a checklist of approximately 80 questions covering the overall concept, manufacturability, permeability, mechanical stability, and chemical behaviour and long-term stability, the project team assessed national and international backfilling and sealing concepts for shaft seals, drift seals, and backfill material in rock salt, clay host rock, and crystalline host rock. Guided interviews with a total of ten experts, including representatives from TU Bergakademie Freiberg, VTT, the Geological Survey of Finland, ONDRAF/NIRAS, and NAGRA, supplemented this assessment with undocumented practical experience.
Findings
Well-developed backfilling and sealing measures are available internationally only for a limited range of geological conditions, including rock salt at depths of up to approximately 1,000 m, crystalline host rock at depths of up to approximately 500 m (without containment-providing rock zone), and clay or Opalinus Clay sites at depths between 220 and 500 m. Available experience decreases with increasing deviation from these reference cases. For several combinations of conditions relevant to the German site selection procedure, particularly greater depths in crystalline host rock and in clay host rock, international experience is limited or non-existent. On this basis, the project team identified specific knowledge gaps, including the handling of corrosion gases during the post-closure phase in clay host rock, the thermal conductivity of bentonite, removal of the excavation-damaged zone in clay host rock, and sealing of the containment-providing rock zone in crystalline host rock.
About the Project
The VerfüllEND research project started in March 2024 and runs until December 2026. It was funded by the German Federal Company for Radioactive Waste Disposal (BGE) and carried out by BGE TECHNOLOGY GmbH; the project team also included colleagues from BGE.
Outlook
Test programmes should be developed for the identified knowledge gaps. The state of the art in science and technology regarding backfilling and sealing measures should be reviewed regularly as the site selection procedure progresses and further developed in line with each stage of the procedure.