CORROSION OF BREACHED ALUMINIDE FUEL UNDER POTENTIAL REPOSITORY CONDITIONS

摘要

As part of the U.S. National Spent Nuclear FuelrnProgram directive, aluminide fuels (UAlx) are being testedrnunder potential repository conditions to provide data onrnthe leaching of fissile and fission products. Through 183rndays of exposure to saturated vapor and dripping J-13rnwater at 90°C, the fuel coupon remained in excellentrnmechanical condition. Only a tarnishing of the surfacerncould be observed and no spalled products were found.rnThe release of uranium varied from 0.23-2.9 mg/m2/dayrndepending on the specimen and test interval, but wasrnsimilar in magnitude to irradiated UAlx flowthrough testsrnand UO2 drip tests. Most (87%) of the released uraniumrnsorbed to the vessel walls. Colloids were detected in thernleachate samples and dynamic light scattering analysis ofrnone leachant indicated a bimodal population. No uraniumrnor aluminum bearing colloids were found. Thernmechanism for alteration is consistent follows from dryrnoxidation experiments on UAlx (initial corrosion) andrnhumid UO2 oxidation (subsequent paragenesis). Solidrnstate conversion of UAlx into UO2 and free Al is followedrnby further oxidation, dissolving and reprecipitating arnhigher oxide and where a thin layer of water forms on thernsurface. The gel layer provides a thick media where lessrndisordered crystals may form and more uniformly coverrnthe sample surface. Although the surface of the fuelrntransformed rather quickly into a gel-layer and uranylrnoxyhydroxides, the release of uranium to solution wasrncomparable to those measured in irradiated UO2 fuels.rnGiven this, an accurate assessment of the long-termrnrelease of fission products and actinides from irradiatedrnaluminide fuels will require longer testing periods thanrncarried out under this program.