FE-G: Gas dynamics over 10 years at the Full-Scale Emplacement experiment (Mont Terri, CH)

This is the authors' abstract. We don't add key points for this paper.

The long-term safety of deep geological repositories of radioactive waste can be affected by gas production, transport and consumption, i.e. via alteration of the chemical environment and/or gas pressure build up. The Full-scale Emplacement (FE) experiment recreates a 1:1 scale spent fuel (SF) emplacement drift constructed in the Underground Rock Laboratory at Mont Terri (Switzerland). FE is inside Opalinus Clay, with heaters simulating canisters and granular bentonite as buffer material. Since 2014, FE-G combines on- and off-site measurements of gases in the FE experiment, providing data to monitor and validate the prediction of gas safety-relevant processes. In this poster contribution we will present results from 10 years of gas monitoring, with particular focus on: The observed rapid loss of gaseous O2 after emplacement, with current understanding of (ir)reversible processes related to O2 from 3-D reactive transport model (COMSOL) investigations; The role of noble gases, in particular 4He, to describe the ongoing gas exchanges via diffusion (and advection) among the Opalinus Clay, the emplaced bentonite and the niche outside the emplaced tunnel.   Acknowledgements Swisstopo and Mont Terri Consortium Bill Lanyon (Fracture Systems Ltd) for modelling support Companies supporting field and lab work (Entracers, Solexperts, Hydroisotop)