Leaching of SIMFUEL in simulated granitic water: comparison to results in demineralized water

Static leaching of SIMFUEL in granitic water at 200 C for durations up to 1000 h under argon atmosphere and in presence of granite monoliths was studied. Three simulated burnup compositions (3, 6, and 8 at.%) were used. The results did not indicate any clear burnup effect. The analysis of the leachates showed that the amounts of dissolved fission products and uranium were low under these experimental conditions. With the exception of U and Mo, measurable concentrations were found only in the rinse solutions of the container and the granite monolith. Ceramographic examination revealed that surface attack occurred after the shortest leaching time and did not appear to increase with time. Electron microprobe analysis revealed that silico-aluminates were present on the leached surfaces. Small, needle-shaped deposits were visible on the surface only after the longest leaching times. Significant differences were observed when leaching SIMFUEL and UO2 at 200 C in demineralized water in air. Under these latter conditions, leach rates and amounts of surface redeposition of uranium in a higher oxide form (e.g., schoepite) were significantly higher. A progressive coverage of the surface by redeposited crystals was observed for increasing leaching times. (orig.)