Abstract
The Canadian Standards Association (CSA) Standard N285.8 requires evaluation of a detected in-service flaw in CANDU Zr-2.5Nb pressure tubes for crack initiation due to fatigue. Fatigue crack initiation experiments had been performed on notched specimens from irradiated and unirradiated pressure tube materials in a laboratory air environment. A statistical-based fatigue crack initiation model that covers the effects of flaw root radius, load rise time and irradiation had been developed, which was documented in the paper PVP2014-28942. The number of load cycles to fatigue crack initiation is predicted to decrease with an increase in load rise time. The load rise times of fatigue test data used in the development of the statistical-based model are no more than 50 seconds, however, there are transients with load rise times as long as nominally 60 minutes during the operation of CANDU reactors. A number of additional fatigue test data from both irradiated and unirradiated pressure tube materials with load rise times up to 1800 seconds have been generated to validate the application of the statistical-based model to transients with long load rise times. The statistical-based model has also been refined by including those additional fatigue test data into the model development. The validation and refinement of the statistical-based fatigue crack initiation model in an air environment have been documented in this paper.
