The diffusion properties of the Opalinus Clay are comparable with those of other clay-rich rocks with similar porosity (Fig. 5‑55). The porosity is related to the (maximum) burial depth, and the effective diffusion coefficient of a water tracer approximately follows a power law (Archie) relationship with the porosity.

Fig. 5‑55:Comparison of Opalinus Clay diffusion coefficients with data from other clay-rich rocks worldwide

D_e of HTO for Opalinus Clay from the JO, NL and ZNO siting regions plotted at the diffusion-accessible porosity. International examples are from the Clay Club Catalogue (OECD/NEA 2022) plotted at the indicated water-loss porosity. For the international samples, points indicate best estimates, bars represent minimum and maximum values. 1: Wakkanai Formation at Horonobe (JP, maximum burial depth: 1'200 m), 2. Ypresian Clay at Kallo/Doel (B, 450 m), 3: Boom Clay at Mol (B, 215 m), 4: Callovo-Oxfordian at Meuse/Haute Marne (F, UA unit, 850 m), 5: Toarcian-Domerian at Tournemire (F, 1'300 m), 6: Georgian Bay Formation at Bruce Site (CDN, 1'520 m); 7: Queenston Formation at Bruce Site (CDN, 1'450 m). Maximum burial depths as an indication for consolidation (best estimates or average values).