b'Accomplishments:An ultra-highvacuum permeation testing system (Figure 1) was designed and constructed at the Low Activation Materials Development and Analysis (LAMDA) lab of Oak Ridge National Laboratory (ORNL), which has a high detection resolution of 8.0710-12 atm cc/s and 2.8310-12 atm cc/s for helium and deuterium, respectively. The tubular samples were hermetically mounted to a stainless steel sample fixture using epoxy. A special irradiation vehicle was designed and fabricated toFigure 1. Cross-sectional test SiC-based cladding undermacrostructure of as-cast Fe-conditions representative of LWR12Cr-6Al-2Mo-0.2Si (C26M) to allow for a constant tube outerbase alloyssurface temperature in the range of 300~350C under a representative high heat flux (~0.66 MW/m2)Figure 2. Helium leakage rate of SiC/SiC composite tubes following neutron during one cycle of irradiation in theirradiation (300~500C, 2dpa, HFIR) under high (HHF) and low (LHF) heat flux as a High Flux Isotope Reactor (HFIR)function of helium pressure.(equivalent to 2 dpa). The permeation testing system was employed totube irradiated under a low heat fluxcompared with the same type of SiC/evaluate the hermeticity of the SiC/SiCremained hermetic. All the otherSiC composite tube. Note that HHF tubes, provided by General Atomicstubes, following neutron irradiationneutron irradiation leads to a higher (GA), French Alternative Energies andunder both high and low heat fluxes,helium leakage rate for the studied Atomic Energy Commission (CEA),lost their gas tightness. It is evidentsamples compared with samples and Korea Atomic Energy Researchthat neutron irradiation under HHFfollowing LHF irradiation. The loss Institute (KAERI), following high-heatleads to increased helium leakageof hermeticity of the studied samples and low-heat neutron irradiation.rates compared with the same sampleindicates the presence of penetrating The results (Figure 2) show that thebefore and after irradiation. Althoughcracks. Ongoing work aims at helium leakage rate increased witha comparison of the same sampleunderstanding the failure mechanisms increasing helium pressure and thenbefore and after neutron irradiationby combining thermomechanical started to level off when the pressureis not available, neutron irradiationanalysis and postirradiation rose above 50 torr. Only one neutron- significantly altered the heliumexamination (PIE).irradiated GA SiC/SiC compositeleakage rate of the studied samples 2019|AFC ACCOMPLISHMENTS 85'