SPECIATION AND MOBILITY OF URANIUM IN TAILINGS MATERIALS AT THE U-PRODUCTION LEGACY SITE IN UKRAINE.

The results of the study on speciation and mobility of uranium in the ore processing residues in the Centralny Yar tailings (CY, former uranium processing site - Pridneprovsky Chemical Plant in Ukraine) are presented. Due to poor neutralization sludge material was dumped into the tailings body in acidic state. Several incidents with breakage in the pipeline transporting complex radiochemical solutions caused radioactive material spillover onto the tailings surface. Two features of radiological concern were identified - secondary contamination of the tailings surface amid elevated gamma dose rates, and excessive migration of radionuclides of U/Th decay series in strong acidic conditions within the tailings body. The monitoring data collected during 2005-2017 showed fast migration of uranium from the tailings body into the groundwater with specific activity varied in the range from 1 to 20 Bq/L. To support this finding the experimental studies aimed to obtain physical and chemical speciation of uranium in the tailings materials in existing and simulated conditions were undertaken. This was conducted by application of modified BCR sequential extraction methods followed by assessment of uranium speciation in equilibrium conditions, using the geochemical modeling tool MEDUSA coupled with the HYDRA database. [ABSTRACT FROM AUTHOR]