HIGH-PRESSURE HYDRIDING OF ZIRCALOY

The hydriding characteristics of Zircaloy-2(Zry), sponge zirconium (as a liner on Zry plate), and crystal-bar zirconium exposed to pure H-2 at 0.1 MPa or 7 MPa and 400 degrees C were determined in a thermogravi metric apparatus. The morphology of the hydrided specimens was also ex amined by optical microscopy. For all specimen types, the rate of hydr iding in 7 MPa H-2 was two orders of magnitude greater than in 0.1 MPa H-2. For Zry, uniform bulk hydriding was revealed by hydride precipit ates at room temperature and on one occasion, a sunburst hydride. In a ddition, all specimen types exhibited a hydride surface layer. In a du plex Zry/sponge-Zr specimen, Zry is more heavily hydrided than the spo nge Zr layer.