The chemical composition of groundwater plays an important role in determining the safety of geological disposal facilities for radioactive waste. This is particularly relevant to the chemical stability of the buffer material and the resilience of the waste canisters. The chemical factors that affect a safety assessment include salinity, redox potential, pH and the concentration of a number of key chemical components. It is expected that some disposal facilities, for example at Olkiluoto in Finland and at Forsmark in Sweden, will be located in higher strength crystalline rock, where the groundwater is largely constrained to flow through sparse fracture networks. Until now, safety assessments for such facilities have followed one of two approaches:

(i) modelling transport and chemical interactions using an equivalent continuous porous media (ECPM) representation of the fracture network;

(ii) utilising explicit discrete fracture network models to calculate steady state pressure solutions and then utilising particle tracking to infer the transport properties of the fracture network.

However, a more natural approach is to model the hydrogeochemical evolution in fractured bedrock directly, using an explicit discrete fracture network (DFN) representation. This is the approach considered here.

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