Effect of radial hydride on delayed hydride cracking behaviour of Zr-2.5Nb pressure tube material

Abstract

Delayed Hydride Cracking (DHC) behaviour of Zr-2.5Nb Pressure Tube (PT) material used in Indian 200MWe Pressurised Heavy Water Reactor (PHWR) containing radial hydrides and circumferential hydrides was studied in the temperature range of 200–250 °C. A section of the PT was charged with 70wppm of hydrogen and successfully subjected to re-orientation treatment to form radial hydride. The radial hydride in the reoriented tube was characterised by the hydrogen continuity co-efficient (HCC). It was observed that the average DHC velocity (VDHC) for the radial hydrided sample was 2.5 and 1.85 times faster than the circumferential hydrided sample at 200 and 225 °C, respectively. The VDHC at the temperature of 250 °C, for both the radial hydrided and the circumferential hydrided sample were comparable. The average VDHC for circumferential hydrided sample varies linearly with 1/T while it was observed to vary non-linearly with 1/T for radial hydrided sample. The VDHC of the radial hydrided sample was observed to increase with increase in the stress intensity factor, whereas for circumferential hydrided samples the VDHC was independent of stress intensity factor in the range of 18–45MPa.m1/2.