Postirradiation examinations of low burnup U₃Si₂ fuel for light water reactor applications

The United States Department of Energy Advanced Fuels Campaign in collaboration with industry is working to develop enhanced accident tolerant fuels for light water reactors. The initial irradiations of these concepts were performed in the Idaho National Laboratory Advanced Test Reactor using drop-in style irradiations. These irradiations are collectively referred to as Accident Tolerant Fuels 1 (ATF-1). The postirradiation examination of ATF-1 has begun and some concepts have now completed initial examination. This work is focused on postirradiation examination data of U₃Si₂ fuels at low burnup (i.e., 3Si₂ pellets show limited cracking in comparison to the expected behavior of UO₂ at same power level. In addition, gamma spectrometry data did not reveal migration of fission products. Minor homogeneous hardening along the pellet radius due to accumulation of fission products and radiation damage was measured by microindentation. The fission gas release and swelling remain very low. Formation of fission gas bubbles resolvable with optical microscopy occurs from the pellets center outward to approximately 60% of the fuel pellet radius. The overall data suggest a good performance of this accident tolerant fuel candidate at low burnup.