Journal of Nuclear Fuel Cycle and Waste Technology

The long-lived fission products 79Se and 99Tc have been considered as the major concern nuclides for the disposal of radioactive waste because of their high solubilities and the existence of anionic species in natural water. In this study, the solubilities of FeSe2(s) and TcO2(s), known as respective Solubility Limiting Solid Phase (SLSP) of selenium and technetium, were measured in the KURT (KAERI Underground Research Tunnel) groundwater under various pH and redox conditions. And their solubilities and major species were also calculated using geochemical codes under conditions similar to experimental solutions. Experimental results and calculation for FeSe2 show that the solubility of selenium was found to be below 1x10-6 mol/L under the condition of pH 8 9.5 and Eh=-0.3 ~-0.4 V while the dominant species was identified as HSe-. For TcO2, the solubility of technetium was found to be 5x10-8 1x10-9 mol/L in the solutions of pH 6 ~ 9.5 and Eh<-0.1 V, while the dominant species was TcO(OH)2. However, when the Eh of the solution is -0.35 V, TcO(OH)3 - and TcO4 - are calculated as the dominant species at pH 10.5 ~ 12 and pH>12, respectively.

Keywords

Selenium,Technetium,Solubility,Species,Groundwater