Effect of radial hydrides on fracture behavior of Zr-2.5Nb pressure tube material

The fracture behavior of Zr-2.5Nb pressure tube (PT) material containing radial hydrides with hydrogen concentrations between 30 and 300wppm was evaluated between 25 and 300 degrees C covering lower-shelf, transition and upper-shelf temperatures. The fracture toughness vs. temperature curves showed S curve behavior. In the lowershelf region, specimens failed in a brittle manner with unstable crack growth, whereas in the upper-shelf region, specimens showed ductile fracture with stable crack growth. The S curve shifted to higher temperatures with hydrogen concentration, with saturation of lower-shelf, transition and upper-shelf temperatures between 100 and 300wppm. The fracture behavior was rationalized in terms of the strength of the Zr-2.5Nb PT material, hydrogen terminal solid solubility during dissolution, stress in the hydride during hydride dissolution, the hydride continuity coefficient and the strength of the embedded hydrides.