b'The second-generation Cr coating on the outer surface of SiC/SiC composite cladding was developed to mitigate hermeticity loss via irradiation-induced micro-cracking found by a PIE of the prototypic cladding materials. (Figure 1). The detector spot size was reduced to improve measure-Figure 3. X-ray radiograph of thement accuracy. The thermal prop-irradiated SiC/SiC compositeerty was used to back-calculate tube showing the through-thickness crack in blue the irradiation temperature and its distribution by using a finite element model to ensure the intended irradiation condition. He leak tests were conducted before and after irradiation (Figure 2) and revealed that irradiation with the temperature gradient caused a loss of tube hermeticity. This is because irradiation with the temperature The evaluation methods usedgradient causes cracking damage included a laser flash thermalattributed to strain from the gradient diffusivity test, a gas permeabilityof irradiation-induced swelling. measurement using a leak detectorThe x-ray computed tomography and permeation gas station, andanalysis proved that this occurred, x-ray computed tomography. Aand through-thickness cracking new diffusivity test method waswas found locally (Figure 3). In developed specifically for the tubesummary, PIE generated the critical geometry. This study investigatedexperimental data that the proto-the thermal diffusivity of couponstypic SiC/SiC composite cladding with a curvature machined fromneeds to be improved to mitigate the SiC/SiC composite tubes via ahermeticity loss.modern flash diffusivity apparatus 78 2021|AFC ACCOMPLISHMENTS'