Comparative Investigation of Palladium Alloys Structure and Evolution of Properties in Tritium Medium at 400 °C

Investigation of binary (Pd20Ag) and V-1 (Pd15Ag0.6Pt0.6Ru1.0Au0.2Al) alloys as a material for a palladium diffuser in an ITER Fuel Clean-Up System has been performed. Tritium exposure was as long as 2300 h. Calculated He-3 concentrations in the alloys reached 600 and 500 appm respectively. It was shown that after an initial increase of the alloy lattice parameter, its further decrease took place. Positron spectroscopy data have shown that simple defect concentration in the alloys was stable, but Helium bubble size and its concentration rose significantly during Tritium exposure. By microstructure investigation it was shown that Helium bubbles nucleation was uniform through the whole grain volume but bubble growth was observed predominantly along dislocations and grain boundaries. Tensile property investigations at high temperature (400 °C) have revealed a significant elasticity decrease in the alloys under study.