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Abstract

It is shown that in addition to the precipitation of small gas filled pores, there is a pronounced reduction in the grain size at the surface of UO(2) fuel at high burn-up. These microstructure changes were first observed when the local burn-up exceeded 70-80 MWd/kgM. Generally, the change in microstructure does not penetrate more than 200 microns. However, in a HWR fuel irradiated to 75 MWd/kgM a large part of the pellet cross-section was found to have been affected. Temperature predictions for this fuel suggests that it is the restructuring accompanying thermally activated fission gas release at 1100 to 1200 C that limits the distance over which the microstructure changes occur. Apparently, the formation and fission of Pu is not directly responsible for the change in fuel microstructure. The porosity evidently contains most of the fission gas that is lost from the UO(2) lattice in the region where the microstructure changes take place.

Additional information

Authors: WALKER C T, JRC Karlsruhe (DE);KAMEYAMA T, CRIEPI, Tokyo (JP);KITAJIMA S, CRIEPI, Tokyo (JP);KINOSHITA M, CRIEPI, Tokyo (JP)
Bibliographic Reference: Paper presented: Fall Meeting of the European Materials Research Society, Strasbourg (FR), Nov. 27-30, 1991
Availability: Available from (1) as Paper EN 36393 ORA
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