PNNL

Abstract

We show evidence for the transport of the noble metal phase fission products into an oxidized zirconium metal cladding liner from high burnup UO2 spent nuclear fuel (ATM-109, Quad Cities, Boiling Water Reactor Fuel, 80 MWd/KgU). The fission product phase appeared as agglomerates containing the typical five metals (molybdenum, technetium, ruthenium, rhodium, and palladium) and were associated with the fission gas Xe within an oxidized portion of the zirconium liner. When Xe was not found, the noble metal phase particles within the cladding were often associated with void spaces that probably contained gaseous fission products that escaped during sample preparation. The particles also contained significant quantities of tellurium and were non-uniform with Pd/Te separated from the other elements. Void and particle number densities / volumes were correlated with each other and increased toward the fuel interface with the oxidized Zr liner. Embedded fission products in cladding may have implications for fuel performance at high burnup, advanced designs of accident tolerant fuels, and short- and long-term storage behavior of high burnup fuels where fuel cladding interaction has occurred.