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

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 degrees 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 (V-DHC) for the radial hydrided sample was 2.5 and 1.85 times faster than the circumferential hydrided sample at 200 and 225 degrees C, respectively. The V-DHC at the temperature of 250 degrees C, for both the radial hydrided and the circumferential hydrided sample were comparable. The average V-DHC 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 V-DHC of the radial hydrided sample was observed to increase with increase in the stress intensity factor, whereas for circumferential hydrided samples the V-DHC was independent of stress intensity factor in the range of 18-45MPa.m(1/2). (C) 2020 Elsevier B.V. All rights reserved.