Speciation and solubility calculations for waste relevant radionuclides in Boom Clay: Updating calculations of ER-0411 using ThermoChimie v10a

ONDRAF/NIRAS (O/N) decided ThermoChimie to be used as the new reference thermochemical database to perform geochemical calculations supporting the assessment of the behavior of HLW-relevant radionuclides in different scenarios and under different environmental conditions. At SCK CEN geochemical speciation and solubility calculations in the past were however carried out using the in-house developed thermochemical database ‘MOLDATA’. For the purpose of knowledge transfer, these calculations need to be updated by using the currently assigned reference database ThermoChimie v10a. This report describes the updates, where needed, of the solubility and speciation calculations for 27 waste relevant elements done by Salah and Wang (2017) using ThermoChimie. The results illustrated that there are no increasing solubility and less sorbing species of RN predicted as the result of replacing MOLDATA by ThermoChimie. There is no change of solubility and/or speciation for 23 of the 27 elements considered. There are observable changes on solubility and/or speciation of nickel, tin, thorium, and uranium, thus updates on these 4 elements are documented. One important conclusion from this present report is, that observed differences on speciation and solubility predicted by the two databases seem to be merely caused by inclusion of new data in ThermoChimie. No flaws are noticed in neither of the databases so far, although questions remain why and how some of the new thermodynamic data and/or values were selected for ThermoChimie.