| Microstructural studies were conducted on U-7wt%Mo/Al-2wt%Si fuels focusing on their microstructure after fabrication and during irradiation. Si was shown to suppress the growth of the fuel-matrix interaction layer formed between the Al matrix and the U-7wt%Mo fuel. The fuel-matrix interaction layer was shown to be nano-crystalline in structure after fabrication with a grain size of ∼30 nm. During irradiation, the fuel-matrix interaction was shown to be amorphous. The amorphous fuel-matrix interaction layer shows stable fission gas bubble development throughout with Si concentrations above 10 at% minimizing the bubble size. The composition of the fuel-matrix interaction layer is (U,Mo)(Al,Si)2-7. An amorphous fuel region forms between the fuel-matrix interaction layer and the crystalline fuel and is Si enriched. The chemical composition of this region is (U,Mo)3-4(Al,Si). The amorphous fuel region forms during irradiation due to radiation enhanced diffusion. The region shows large undesirable fission gas bubbles at high burnups that are similar to those seen in U3Si fuel. The crystalline fuel region shows an FCC oriented bubble superlattice in the bulk of the fuel grains. The bubble sizes range from 3-4 nm with a lattice parameter of 11-12 nm. At a fission density of 6.3x1021 fiss/cm3, the bubble superlattice collapses with only small residual pockets of the bubble superlattice remaining. Using the experimental physical properties of the bubble superlattice, the bubble nucleation factor, the bubble resolution rate, and the gas-atom diffusion coefficient were found using an intragranular model. Their respective values are 5x10-3, 26.6 sec-1, and 5.7x10-22 m2/sec. These values are in consistent with literature values for UO2 fuels. |
