Positron Spectroscopy of Defects in Hydrogen-Saturated Zirconium

Zirconium alloys, such as Zr-1Nb are widely used as cladding materials for nuclear fuel elements of light water reactors. Hydrogen embrittlement problem causes degradation of these parts of nuclear reactors. It is known, that hydrogen uptake causes changes in microstructure and defect structure of metals. The aim of this work is study of Zr-1Nb alloys’ defect structure after hydrogen saturation up to the concentration of 600 ppm. Saturation of hydrogen was carried out from the gas phase under high temperature and pressure. This study reveals the increase of average positron lifetime with the increase of hydrogen concentration. Value of the average positron lifetime achieves plateau when the concentration of hydrogen is about 600 ppm. Also the following effects were detected in the material after hydrogen uptake up to different concentrations: crystal lattice expansion, dislocations and vacancy-like defects formation, as well as the defect-hydrogen complexes formation.