CREEP DEFORMATION AND RUPTURE PROPERTIES OF UNIRRADIATED ZIRCALOY-4 NUCLEAR-FUEL CLADDING TUBE AT TEMPERATURES OF 727-K TO 857-K

Creep deformation and rupture properties of an unirradiated Zircaloy-4 tube were examined at temperatures of 727 to 857 K to obtain data for evaluating spent fuel integrity under the off-normal dry storage condition. Creep tests were carried out on internally gas pressurized tubular specimens with end plugs welded to both ends. The hoop creep strain up to the steady-state creep region was given by the following equation: epsilon = 0.05 {1 - exp[ -10(epsilon-s(t))0.51]} + epsilon-s(t), where epsilon-s = 1.02 x 10(5)(E/T) exp(4060-sigma/E) exp(-Q/RT) (s-1), t is time (s), E is the elastic modulus (MPa), T is the temperature (K), sigma is the applied stress (MPa), R is the gas constant (= 8.314 J/mol K), and Q the apparent activation energy (233 kJ/mol). The total creep deformation curve over the accelerated creep region could also be presented by the equation expressed as a function of true stress formulated on the basis of constant stress creep data. It is inferred that the transition from the steady-state to the accelerated creep region occurs without changing the deformation mechanism. It was also shown that most of the creep strain to rupture exceeded 100% and Zircaloy-4 had an extremely ductile rupture property.