Application of Neutron Radiography and Neutron Diffraction Techniques in Study of Zirconium Hydride Blisters in Zirconium Based Pressure Tube Materials

A programme of examining hydride blisters created in the laboratory on zircaloy pressure tubes and that in the irradiated pressure tube from one of the PHWR , which was suspected to have developed hydride blisters, was undertaken using neutron radiography. It was observed that a zirconium hydride blister of nearly 0.35% of job thickness could be detected using neutron radiography. This work served as a reference in examining irradiated zircaloy pressure tubes from a power reactor with residence time of ~ 8.25 effective full power years. Neutron radiography was also used to study size and shape of the zirconium hydride blisters embedded in the zircaloy-2 pressure tube. The zircaloy and Zr-2.5%Nb pressure tube coupons in which hydride blisters were created in the laboratory were also studied using neutron diffraction to identify the zirconium hydride phase and to find the extent to which the sample has hydrided. In order to determine the amount of hydride phase, a Rietveld refinement of the neutron diffraction pattern was carried out.