Tests of full-size pressure tubes and compact tension specimens having several widths are carried out with emphasis on the size effect on the fracture toughness of the pressure tube material, which is made of heat-treated Zr-2.5Nb. The hydrogen concentration of the specimens ranges from 10 to 400 ppm, and the test temperature from room temperature to 573 K.
In the pressure tube burst tests at room temperature using radial hydrided materials, fracture toughness at maximum pressure KC decreased rapidly with hydrogen concentration in the region where the concentration was less than 100 ppm. In the region where the hydrogen concentration was higher than 100 ppm, KC slowly decreased with increased concentration. For materials having radial hydrides at a hydrogen concentration of 200 to 300 ppm, a steep brittle-ductile transition was observed at about 550 K.
Fracture toughness KC shows strong dependence on specimen size, increasing and approaching that of pressure tubes with increased specimen width for a ductile material. This size effect of fracture toughness can be determined by a failure assessment method in which the Dugdale model is used.