Volume 2, Issue 8 (September 2005)
Delayed Hydrogen Cracking Velocity and J-Integral Measurements on Irradiated BWR Cladding
Propagation of an axial crack has been characterized by means of the Pin-Loading Tension (PLT) test. The same experimental arrangement is used for the Delayed Hydrogen Cracking (DHC) and for the J-integral measurements. The DHC tests are performed under variable temperature and/or load conditions simulating a variable PCMI. Tests have been performed in air on unirradiated SRA Zircaloy-4 tubing and irradiated BWR Zircaloy-2 cladding containing from 30–350 ppm of hydrogen. Variable loading facilitates DHC: in the experiment at 300°C a crack velocity as high as 9.3·10−7 m/s (80 mm/day) has been observed for irradiated cladding. V-K curves or diagrams of DHC crack velocity, V, as a function of stress-intensity factor, K, are suggested for different BWR claddings. Despite a limited amount of tests, the V-K curves appear to depend on the type of cladding. DHC does occur at much lower stress intensities compared to the Kc converted from the J0.2 values, confirming DHC to be the dominating secondary failure crack propagation mechanism in BWR cladding.