Extent of oxidising conditions in the host formation

This report describes the set-up and installation of an experiment in the underground research laboratory HADES to evaluate the extent of the oxidised zone around. Two parts of the underground laboratory, namely the Test Drift (20 years of ventilation) and the Connecting Gallery (3 years of ventilation) are compared. The oxidised zone is for both parts limited to about 1 meter around the gallery. These experimental results are compared with scoping calculations of oxygen transport into the clay and sulphate transport within the clay, for both taking into account diffusion and advection near the gallery. These scoping calculations fit very well with the observations, indicating that ventilation for 20 years or less will result in an oxidised zone of about 1 meter. Longer ventilation times will increase the extent of the oxidised zone, but the process is very slow. This research is of particular importance for supporting strategic decisions considering the operational phase. Moreover, the effect of oxidation on the long-term performance of the host rock or on the evolution of the Engineered Barrier System (EBS) is not known up to date, but might be of importance for PA calculations.