GAST: Gas tests at the GAs permeable Seal Test – Successes and lessons learned (Grimsel Test Site, CH)

The degradation of organic substances and metal components is expected to generate gases in radioactive waste repositories. Therefore, gas-permeable plugs and seals concepts have been developed to manage gas pressure development while ensuring the containment of radionuclides and other non-radioactive contaminants.

The Gas permeable Seal Test (GAST) is an international project aimed at testing the feasibility and functionality of a gas-permeable seal under realistic scale and boundary conditions. The seal is made of a mixture of 80/20% sand/bentonite mixture and emplaced in the Grimsel Test Site (Switzerland).

After a decade of progressive seal saturation and pressurisation with water, gas flow tests were carried out between May 2022 and August 2023. Noble gases (i.e. He, Ar, Xe) were used as tracers of gas transport through the seal section of the experiment.

Consolidated interpretation of the results indicate that the gas path developed quickly through the seal (end-to-end-flow). Furthermore, the presence of the injected gas tracers both at the extraction point and in gas samples taken from inside the emplaced sand/bentonite layers demonstrated the existence of a gas phase within the seal. Finally, the absence of measurable gas leaks within the tunnel further confirmed the overall functionality of the seal system.

 

Acknowledgements

Grimsel Test Site Staff for support onsite

Solexperts for hardware components, support in field and with measurements

Entracers and Hydroisotop for onsite and offsite gas analyses