Nuclear Science User Facilities 78 throughout the precipitate (as indicated by EDS), and by variations in crystal structure, orientation, or dislocation density among different parts of the precipitate (as suggested by HRTEM).ASTAR results indicate that the majority of precipitates are located at random high-angle grain boundaries. Significant challenges were encountered during EELS study and no useful EELS results were obtained.The challenges were ascribed to the fact that theTEM specimen was not thin enough.TheTEM specimen was prepared previously in the Electron Microscopy Laboratory (EML) and, due to the significant radioactivity, it could not be further thinned at the Center for Advanced Energy Studies (CAES). In addition, it could not be shipped back to EML for further thinning due to the limit in time and budget for this Rapid Turnaround Experiment (RTE) project. Although the EELS study was not successful, the other data (STEM, EDS, TEM/HRTEM, and ASTAR) enabled significant accomplishments toward the technical goals, which rendered this project successful. Figure 1 showsTEM and STEM images of a fission product precipitate and EDS line scan and mapping results. InTEM images (a) and (b), there is contrast variation throughout the precipitate, although the precipitate appears to have uniform contrast in STEM image (c). EDS line scan and mapping indicate that the precipitate is rich in Pd, however, there is variation in the Pd concentration throughout the precipi- tate. Note that Si and C concentrations are from the SiC matrix. Figure 2 displays STEM,ASTAR, and EELS results.The ASTAR results indicate that the precipitate highlighted in (a) is located at a random high-angle grain boundary with a misorienta- tion angle of 30 degrees. Note that this precipitate is the same with the one studied in Figure 1.Although it is clear from EDS results that this precipitate is Pd‑rich, no peak corre- sponding to Pd is evident in the EELS spectrum (c); the only peak present in the EELS spectrum corresponds to C (that comes from the SiC matrix). From the zero-loss peak (d), the thick- ness of the precipitate is computed as 0.54 electron mean free path, which is too thick to get good EELS results. In order to obtain good EELS signals, the thickness needs to be on the order of 0.1 to 0.2 electron mean free path.Thickness measurements were conducted using EELS at many different locations and it was found that theTEM specimen is too thick for EELS study. Figure 3 showsTEM, HRTEM, STEM, and EDS results on another fission product precipitate. From theTEM and HRTEM images, there is contrast variation across the precipitate and it appears that there are multiple layers in the precipitate in the thickness direction of theTEM specimen. From the HRTEM images, it appears that the parts with different contrast in the precipitate have the same crystal