Thermodynamic modelling of radioactive waste disposal. Assessment of near-field solubility

This report describes the modifications to the aqueous speciation and solubility data in the HArwell Thermodynamic database for CHemical Equilibrium Studies (HATCHES), since its initial release in 1987. Updates to the database for sixteen priority radioelements of relevance to the field of radioactive waste disposal are included. Where modifications were made, these were initiated to maintain consistency with available experimental data. The revised thermodynamic database (HATCHES, Version 4.2) has been employed to predict the near-field solubility of each radioelement in water equilibrated with the Nirex Reference Vault Backfill water and the near-field groundwater at three different Eh values (-410 mV, -250 mV and -100 mV) and, where data are available, at three different temperatures (25 deg C, 50 deg C and 80 deg C). The current version of the HATCHES thermodynamic database is released in October each year and may be obtained from the OECD/NEA. A listing of the database used in this work may be obtained on request from UK Nirex Ltd. (author)