Stress-rupture behaviour of zirconium-2.5 niobium pressure tube alloy of 500 MWe PHWR

Stress-ruptures tests at temperatures 300-450 C and stresses 100-480 MPa on specimens machined from a Zr-2.5% Nb pressure tube, are reported. Rupture stress and rupture ductility (pct. elongation) were analysed by Larsen-Miller parameter. It was observed that the calculated rupture ductility and rupture stress for 105 hours at 300 C were 29 percent and 340 MPa which satisfies the stress criteria for pressure tube design. Further it was noted that at a given temperature, the rupture time obeyed a power-law stress dependency, analogous to the relationship between minimum creep rate and stress and the ductility parameter defined as the product of minimum creep rate and rupture time depended on stress exponent. Based on these observations, an attempt has been made to explain the micro-mechanism of fracture phenomenon. (author). 7 refs., 8 figs., 2 tabs