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The Manufacture and Characterisation of Composite Nuclear Fuel for Improved In-reactor Performance
[Thesis]. Manchester, UK: The University of Manchester; 2017.
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Abstract
Fuel for nuclear reactors with an increased thermal conductivity offers the potential for lower fuel operating temperatures and reduced fission gas release rates. Uranium dioxide (UO2) based composites offer a method of achieving a higher thermal conductivity. Silicon carbide (SiC) and molybdenum (Mo) have been identified as potential candidates for use in a composite fuel material. Uranium dioxide composites were manufactured with the inclusion of whiskers and granules of SiC up to a 30 vol% loading. The manufacturing route used was based on the current process employed to commercially manufacture UO2 fuel, by reductive sintering. Composites containing Mo were manufactured via spark plasma sintering and included loadings of up to 10 vol% Mo. The composites were characterised on their microstructural properties and where appropriate the thermal conductivity was determined by laser flash analysis. The composites containing SiC achieved low densities, <90%TD. A chemical interaction between the UO2 and SiC was observed in both the granule and whisker composites at loadings of 20 and 10 vol% respectively. A hyperstoichiometric uranium silicide phase of USi2 was identified as being produced during the reaction. At a 10 vol% SiC granule loading minimal evidence for interaction was observed but lower grain size and increased porosity were observed in the UO2 matrix. The molybdenum containing composites achieved high densities, >95%TD. The microstructure contained channel like structures of Mo, due to the use of an agglomerated UO2 precursor powder. An increased thermal conductivity was determined for the molybdenum composites. At the maximum measurement temperature of 800°C the increase was found to be 68% in the 10 vol% composites compared to UO2.
Keyword(s)
Accident Tolerant Fuel; Energy; Molybdenum; NFCE; Nuetronics; Silicon carbide; Spark plasma sintering; Thermal conductivity; Uranium dioxide; sintering