Nuclear Science User Facilities 80 Moreover, a novel experimental technique for mapping irradiation temperature in specimens was devel- oped. In this technique, the one-to-one correlation of certain Raman peaks and the lattice swelling of irradi- ated SiC was established [3,4] then successfully applied to determine the radial temperature profile within a thin-walled tube. Despite its limited accuracy due, partly, to the small laser spot size used for the mapping, the developed approach was able to prove the presence of a temperature slope consistent with the predicted for a CVD SiC specimen as shown in Figure 4. The project plans an extensive set of post-irradiation characteriza- tion, starting with non-destructive evaluations (NDE) and followed by destructive evaluations such as cross-sectional microscopy and stress state-characterization involving elevated-temperature annealing. NDEs are focused on detecting and charac- terizing microcracking behavior and the possible resultant changes in gas permeability. Because microcracking due to irradiation-heat-flux synergy is anticipated at or near the inner surface of the tubes, where stress is primarily in tension, sonic or X-ray-probe NDEs are particularly useful. Figure 4. Development of a laser micro-Raman technology to map the irradiation temperature of SiC by post-irradiation thermometry (left), and application of the technology in verifying the temperature gradient across tube-wall thickness during neutron irradiation of SiC samples in Fire Rabbit (right).