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Transmission electron microscopy on UO(2) has been performed for more than 35 years. The features investigated included fission gas bubbles, and fission product precipitates in UO(2), the microstructure of deformed UO(2), and others. More recently, high burnup UO(2) has been investigated in transmission electron microscopy (TEM) and lattice plane resolution was achieved in ion implanted UO(2), but without revealing details of the UO(2) structure or of radiation damage. A phenomenon occurring at extended burnup in UO(2) fuel has recently gained much interest. It is generally termed the RIM effect, since it first occurs in the outer rim of operating fuel. In this outer shell of 150 to 200 mm thickness, the burnup is increased by up to a factor of 2.5 above the cross-section averaged burnup due to neutron resonance capture by U-238 forming fissile Pu-239. The consequence is a grain subdivision process or polygonization: the grains of the assintered UO(2) of typically 10 mm diameter are subdivided into some 1E4 new small subgrains of 0.2 to 0.3 mm size.

Additional information

Authors: MATZKE H, JRC Karlsruhe (DE);WANG L M, University of New Mexico, Department of Earth and Planetary Sciences, Alburquerque (US)
Bibliographic Reference: Article : Journal of Nuclear Materials (1996)
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