Irradiated microstructure of U-10Mo monolithic fuel plate at very high fission density

AFIP6-MkII and RERTR-12 Porosity Data Collection and Analysis for Modeling and Simulation

“…Post-recrystallized grains found in U-Mo dispersion fuels irradiated to 6.3x10 21 f/cm 3 were similar to those seen in monolithic U-Mo samples irradiated to the much higher fission densities [19,20]. The similarities of the structures indicate at fission densities above 6.3x10 21 f/cm 3 grains do not continue subdividing [27].…”

“…These foil samples showed that at high fission densities, U-Mo monolithic fuel can exhibit swelling of ~76% [27]. Focused ion beam (FIB) TEM investigations of monolithic U-Mo fuels uncovered the presence of small, 2 nm-sized intragranular bubbles [27]. Previously, it was thought that large FGB govern the microstructure, and small bubbles are less influential at high fission densities (>7x10 21 f/cm 3 ).…”

“…However, small bubbles (<200 nm) were also prevalent. These foil samples showed that at high fission densities, U-Mo monolithic fuel can exhibit swelling of ~76% [27]. Focused ion beam (FIB) TEM investigations of monolithic U-Mo fuels uncovered the presence of small, 2 nm-sized intragranular bubbles [27].…”

“…However, these samples were irradiated to the high fission densities. A high concentration of smaller bubbles implies these bubbles inhibit grains from swelling by maintaining the high gas inventory inside the smaller, dense bubbles [27]. The large population of small gas bubbles at a high fission density suggests there is something other than fission density determining the evolution of the various sized bubbles in the material [27].…”

Review of the Technical Basis for Properties and Fuel Performance Data Used in HEU to LEU Conversion Analysis for U-10Mo Monolithic Alloy Fuel

“…This is an indication that the models do not fully capture the physics leading to changes in thermal conductivity with irradiation in this fuel system. Additionally, the Bruggeman [47] and Peddicord [48] correlations likely only account for porosity visible by optical microscopy and scanning electron microscopy, missing the substantial amount of fission gasses trapped in nanobubbles, as has been observed via TEM [50], or in solution with the alloy. The under prediction of the reduction in thermal conductivity with irradiation could also be caused by the influence of solid fission products incorporated into the fuel system, as well as the formation of large pores aligned along the interface (rather than the assumed homogeneous distribution).…”