Study of the hydride morphology in the Candu reactor pressure tube modified by heat treatment

The aim of this study is to discuss the morphology (the shape and orientation) of the hydride platelets in the pressure tube material (Zr-2.5%Nb alloy) in function of the modified microstructure by heat treatment.The different microstructures were obtained by annealing and hydrides by hydrogenation (using the electrolytic deposition and the diffusion of the hydrides in the block of samples by a thermal treatment of ageing). The microstructures and hydride morphology were characterised by microscopic analysis, hydrogen content measurements, hydride orientation factor, microhardness Vickers measurements.Based on the results obtained, the increased recrystallization degree involves changes in the hydride distribution. This fact is reflected in the increase of the orientation factor of hydrides and in micro-hardness diminution.