NAGRA Opalinus Clay (…002 - Version 1
FEP 13.4.4 Chemical plume from ILW

Geochemical reactions due to a high-pH plume from cement dissolution 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. The organic content of the ILW waste is too small to lead to an organic plume. The nitrate content of some waste types may be high enough to lead to a temporary plume, potentially leading to oxidising conditions (catalysed by microbes). Since alkaline water may lead to cementation of bentonite seals and backfill, their swelling properties may be adversely affected. This is not considered any further because of the long flowpath (second order effect).