Hydride reorientation in pressure tubes of CANDU nuclear reactors

In CANDU nuclear reactors, zirconium alloys are widely used in key components such as pressure tubes and fuel cladding. Hydrogen absorption from corrosion during reactor operation will result in embrittlement of these alloys and subsequently to material failure. In Zr-2.5% Nb pressure tubes, which contain the fuel and coolant and operate at temperatures near 300o C, when hydrogen picks up to its terminal solid solubility, the formation of hydride precipitates within the bulk of the metal results in any direction. This paper highlights some of the thermo-mechanic conditions for reorientation of the hydride platelets precipitate in radial direction, phenomena which has been identified as the precursor of pressure tube failures (delayed-hydride-cracking, DHC). These results should have significant implications for understanding the DHC phenomena. (Author)