Leaching Behaviour of Low -Activity Alpha-Doped UO 2 .
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Leaching Behaviour of Low -Activity Alpha-Doped UO2. Vincenzo V. Rondinella, Joaquin Cobos*, Thierry Wiss European Commission, Joint Research Centre, Institute for Transuranium Elements, Postfach 2340, 76125 Karlsruhe, Germany; [email protected] *Previously at CIEMAT, Avda Complutense 22, E-28040 Madrid, Spain
ABSTRACT So-called alpha-doped UO2 (i.e. UO2 containing short-lived alpha-emitters) can reproduce the activity levels of spent fuel at different ages. Previous experiments showed significant effects of alpha-radiolysis at relatively high alpha-activity levels (e.g., in the range 108 – 1010 Bq/g). This study shows the results of leaching tests done on low alpha-activity material (106 – 107 Bq/g). UO2 containing ~10 and ~1 wt. % 233U was leached at room temperature in deionized and carbonated water under deaerated conditions. Higher release in carbonated water was observed. A clear radiolytic enhancement of the concentration of uranium in solution was observed for the material containing 10 wt. % 233U. The dissolved U concentration was very close to the values previously observed for higher activity alpha-doped UO2 and confirmed the finding that under relatively high surface/volume condition the measured amount of U in solution is essentially independent of the alpha-activity level. No significant radiolysis effect was detected for the material doped with 1% 233U compared to undoped UO2 after ~4 months of leaching. The postleaching SEM examination revealed no pronounced etching of the surfaces.
INTRODUCTION The so-called α-doped UO2 (i.e., sintered unirradiated UO2 containing short-lived α-emitters) is a valuable tool to study the effects of α-radiolysis on the corrosion behaviour of spent fuel in contact with water [1-5]. Experiments on alpha-doped UO2 are being conducted at several research facilities [6-10] and are included in multinational European collaborations (e.g., the Shared Cost Actions “Spent Fuel Stability” and “In-Can Processes”, co-funded by the European Commission). The results of batch and sequential leaching tests done at ITU at room temperature under unaerated conditions in deionized water and in carbonated water on monolithic [2-3,5,11-13] and crushed [4] samples of undoped UO2 and of UO2 containing 238Pu have been described previously. The concentrations of U measured in the leachates for the 238Pu-doped materials were significantly higher than those for undoped UO2 leached under the same conditions. Moreover, under experimental conditions characterized by relatively high surface to volume (S/V) ratios, the concentrations of U measured in solution for the two doped materials showed no clear differences, in spite of the 100-fold difference in α-activity. This paper presents the results of leaching experiments performed on UO2 containing ~10 and ~1 wt. % 233U in deionized and carbonate water at room temperature under un-aerated conditions and adopting similar S/V configurations as in previous tests. These experiments extend the study of alpha-radiolysis effects on fuel corrosion
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