Transport and leaching of technetium and uranium from spent UO2 fuel in compacted bentonite clay

The transport properties of Tc and U in compacted bentonite clay and the le aching behaviour of these elements from spent nuclear fuel in the same syst em were investigated. Pieces of spent UO2 fuel were embedded in bentonite c lay (rho(d) = 2100 kg/m(3)). A low saline synthetic groundwater was used as the aqueous phase. After certain experimental times, the bentonite clay wa s cut into 0.1 mm thick slices, which were analysed for their content of Tc and U. Measurements were made using inductively coupled plasma mass spectr ometry. Tc analysis comprised chemical separation. The analysis of U was do ne by means of detecting U-236, since the natural content of U in bentonite clay made it impossible to distinguish between U originating from the fuel and the clay. The influence of different additives mixed into the clay was studied. The results showed an influence on both transport and leaching be haviour when metallic Fe was mixed into the clay. This indicates that Tc an d U are reduced to their lower oxidation states as a result of this additiv e. (C) 2000 Elsevier Science B.V. All rights reserved.