Background+for+Calculations+on+Uranium

Back to Main In Akola, Finland, there is a quarry where a Finnish company Imatran Voima carried out test mining of uranium in the turn of 1950s and 1960s. The ore in Askola is mainly uraninite UO 2+x. The mining stopped already in the beginning of 1960s but the site is still valuable for geological and radiochemical investigations. The uraninite occurrence is natural primary mineral, of which uranium has been partly dissolved in the water. Dissolved uranium is released in the environment and partly precipitates as secondary minerals. Studies on transfer and precipitation processes at the site have given valuable information on how uranium behaves in oxic conditions and this information can be utilized in the evaluation of the behavior of spent nuclear fuel (>95% UO 2 ) disposed in a geological repository. In the final repository the reducing conditions will prevail after some time following its closure. There is, however, a possibility of oxic conditions being regained, by radiolysis or oxic glacial melt waters entering the repository environment.

The purpose of the modeling exercise is to find out speciation forms of uranium in the model groundwater and the possible secondary minerals precipitating in oxic conditions. In addition, it will be seen how changing chemical conditions affect the uranium speciation. Modeling is done with the geochemical modeling program PHREEQC available from the internet (http://pfw.antipodes.nl/download.html). The exercise makes use of groundwater data from the site produced by Geological Survey of Finland (GTK).