RRFM 2009 Transactions - European Nuclear Society

Fig. 4.
TEM image showing relatively large fission gas bubbles present in a U-7Mo fuel particle.
3.2.2 Characterization of the U-7Mo/matrix interaction layers
TEM micrographs of the interaction layer are presented in Fig. 5. A weak beam dark field image
using the diffused ring was generated to show the extremely fine microstructural features
present in the interaction layer, and a SAD pattern was generated to show that the interaction
layer was amorphous. In addition, bright field images in focused, under-focused and overfocused
conditions were generated to show the high density of < 2-nm-sized bubbles that were
present in the interaction layer. These bubbles are likely the fission gas bubbles. A final lowmagnification
TEM image is presented to show the interaction layer between the Al-2Si matrix
and the U-7Mo fuel particle.
Compositional analysis was performed in different areas of the interaction layers to determine
the variability of the Si content within the layers. Figures 6 and 7 shows the areas within the
interaction layers where compositional analysis was performed, and Tables 1 and 2 enumerate
the results of this analysis. From this data it can be seen that there is a variability in the Si
content within the interaction layer, along with the U, Mo, and Al. The highest concentrations
measured in the interaction layer for U, Mo, Al, and Si were approximately 19, 9, 90, and 12 at
%, respectively. It appears that the areas of the interaction layers with the fewest small fission
gas bubbles were also the most enriched in Si. This may indicate a higher fission gas solubility
of the material when Si concentrations are higher, which would result in less fission gas bubbles
precipitating out. At some locations fission product Zr could be detected.
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