Abstract
An experimental LWR fuel with high 235U enrichment (8.6%) and large UO 2 grain size (15–20 μm) was analysed by optical microscopy, SEM and EPMA. Although the high burn-up reached (69.8 GWd/tM), the porosity growth in the rim zone was found equivalent to a standard LWR fuel with barely 40 GWd/tM burn-up. Also, the grain subdivision associated with the rim structure was absent or scarcely visible around the pores of the outermost periphery, being evidenced that the three typical features of this structure, i.e. Xe depletion, pore formation and grain subdivision, did not appear simultaneously, but sequentially in this order as the local burn-up increased. According to the results, the use of higher 235U enrichments in LWR fuels may help to shift all these steps to higher local burn-ups, whereas the grain size of the UO 2 matrix may play only a secondary role in the initiation of these processes.
Published Version
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