Effects of hydrogen concentration on fracture toughness of CANDU pressure tube

Abstract

The effects of hydrogen concentration on the axial fracture toughness of Zr-2.5 wt% Nb CANDU pressure tube material have been determined from room temperature to 300℃. The specimens was charged to 50, 100, 150, 200ppm of hydrogen. To observe hydride morphology and measure volume fraction, optical microscope was used. The crack growth during fracture toughness test was measured by direct current potential drop method. Fracture toughness characterized by J-R curve and dJ/da was discussed in terms of hydrogen concentration. As hydrogen concentration increased, hydride volume fraction, thickness and length increased. However, interhydride spacing remained nearly constant. At room temperature, fracture toughness decreased rapidly with increasing hydrogen concentration until hydrogen concentration was below 100ppm. However, fracture toughness remained at a similar level at above 100ppm. Ductile-brittle transition temperature increased slightly when hydrogen concentration increased. At high temperature, fracture toughness also decreased because yield stress increased by hydride volume fraction.