Quantitative Characterization of Hydride Morphologies of Zr-2.5nb Pressure Tubes With Different Hydrogen Concentrations

Abstract

Zirconium hydrides are present in Zr-2.5Nb pressure tubes in CANDU reactors. Experiments have shown that the presence of hydrides can reduce the fracture toughness of the pressure tubes, depending on hydrogen concentration, hydride orientation and temperature. A systematic experimental study was performed to evaluate the morphologies and distributions of circumferential hydrides in an unirradiated pressure tube hydrided to different hydrogen concentrations ranging from 25 to about 180 ppm by weight. Quantitative metallography was performed to characterize the hydride morphology and distribution to determine and compare the number of hydrides, percentage of hydrided area, hydride length, hydride thickness, and inter-hydride spacing as a function of hydrogen concentration.