The Zr-2.5 Nb pressure tubes of CANDU™ (CANada Deuterium Uranium) reactors are susceptible to a crack initiation and growth mechanism known as Delayed Hydride Cracking (DHC), which is a process that involves hydrogen diffusion, hydride precipitation, hydrided region formation and fracture at a flaw-tip. An overload occurs when the hydrided region at a flaw is loaded to a stress higher than that at which this region is formed. Flaw disposition requires justification that the hydrided region overload from normal reactor operating and transient loading conditions will not fracture the hydrided region, and will not initiate DHC. To evaluate the effects of hydrided region overload on DHC initiation, a series of monotonically increasing load experiments were performed on specimens prepared from unirradiated pressure tube materials with the hydrided region formed at flaws with root radii varying from 15 to 350 μm, and blunt notches with and without secondary flaws. Test results indicate that the resistance to overload fracture is dependent on a variety of parameters including flaw geometry, hydride formation stress, loading history, and overload test temperature.

This content is only available via PDF.
You do not currently have access to this content.