TEM characterization of irradiated RERTR dispersion fuel

The irradiation performance of RERTR dispersion fuels depends on the radiation stability of the various phases that comprise a fuel plate. Transmission electron microscopy was performed on a sample taken from an irradiated U-7Mo dispersion fuel plate with Al-2Si matrix to investigate how the presence of Si in the fuel meat matrix impacts the radiation stability of the U-7Mo/matrix interaction layer phase(s). A similar interaction layer that forms in irradiated U-7Mo dispersion fuels with pure Al matrix has been found to exhibit poor irradiation stability. This behavior seems to be due to the fact that it cannot adequately retain fission gases that are generated during irradiation. For the sample from the irradiated U-7Mo/ Al-2Si fuel plate, the interaction layer was observed to be amorphous, like was case for the layer in irradiated U-7Mo/Al dispersion fuel. However, unlike the U-7Mo/Al fuel, this amorphous layer was found to effectively retain fission gases in areas of high Si concentration. The fission gases were observed to be distributed as small (< 2 nm diameter) fission gas bubbles throughout the interaction layer, which were not observed in the interaction layer in irradiated U-7Mo/Al fuel. The presence of these fission gas bubbles seems to correlate to the Si concentration within the interaction layer. When the Si concentration becomes relatively low, the fission gas bubbles agglomerate into fewer large pores. Within the U-7Mo fuel particles, a bubble superlattice was observed where the bubbles were 2 to 4 nm in size. (author)