NAGRA Opalinus Clay (…002 - Version 1
FEP 13.4.5 Alteration of backfill by liner of access tunnels

Geochemical reactions due to a high-pH plume from cement dissolution of the liner can lead to changes in porewater composition and in mineral composition (dissolution, secondary minerals) and can therefore change sorption and solubility properties for the radioelements. Usually the porosity is also affected. Since alkaline water may lead to cementation of bentonite seals and backfill, their swelling properties may be adversely affected. Due to the small amount of cement used for the liners, the effects mentioned above are expected to be small.