Updating equilibrium calculation to derive reference porewater composition of Boom Clay using ThermoChimie v.10a

Ondraf/Niras considers ThermoChimie as the new reference thermodynamic database to perform geochemical calculations supporting the assessment of radionuclide behavior in different scenarios and under different environmental conditions. At SCK CEN some geochemical calculations in the past were however carried out using the in-house developed thermodynamic database ‘MOLDATA’. For a purpose of knowledge transfer some important geochemical calculations done in the past should be updated using the new reference database. This report updates the calculation of the reference porewater composition of Boom Clay carried out in the year of 2004 by applying the newly assigned thermodynamic database ThermoChimie v.10a. Results illustrated that replacing MOLDATA by ThermoChimie does not change the calculated reference water composition except the concentration of iron. The dissolved concentration of iron increased about an order of magnitude due to a different solubility constant of siderite selected in ThermoChimie.