The elastic characterization of zr-2.5%nb alloy pressure tube by ultrasonic methods

The cold-worked Zr-2.5%Nb alloy is used as material for the pressure tubes of CANDU nuclear reactors. It has developed a strong texture due to the limited slip system during extrusion process, leading to anisotropic properties. The material properties are strongly dependent on the orientation distributions of grains. For this reasons result a directional anisotropy of elastic coefficients. During the service life in reactor, diffusion of hydrogen and/or deuterium in the pressure tubes wall may occur. Zirconium alloys have a low solubility for hydrogen. Thus, when solubility limits are exceeded, a brittle second phase (hydrides) appear. The hydrides, even in small concentrations, can potentially have a dramatic effect on the structural integrity of zirconium alloys nuclear components. To characterize the degree of anisotropy and the hydrogen influence it is necessary to determine the anisotropic elastic modulus on the main directions (axial, circumferential and radial) of the tube samples. In the present paper, the most usual elastic modulus on a given direction (axial, circumferential and radial) of the tub (Zr-2.5%Nb alloy) were investigated using non-destructive method based on measurements of ultrasonic velocity. Thus, both longitudinal VL and transversal VT phase velocities have been experimentally determined for each direction. (authors)