Evolution of a defect structure of Pd–Ag alloys during tritium exposure

Pd–Ag alloys, a material for palladium diffuser of the ITER fuel clean-up system, were investigated after long-term usage exposition in tritium. Nucleation and evolution of the alloy structure defects as a result of a radiogenic helium-3 accumulation have been examined using electron microscopy, positron annihilation and X-ray analysis. The types of helium containing defects and their characteristics were determined. The early stage of helium bubbles forming was observed. It was shown that the simple defect concentration decreased slowly and helium-3 bubble sizes and concentration increased during the tritium exposure.