Neutron diffraction investigation of phase compositions in as received and modified Zr–2·5Nb pressure tube materials

Abstract

Zr–2·5Nb alloy is used for the pressure tubes in CANDU [CANDU® (CANada Deuterium Uranium) is a registered trademark of Atomic Energy of Canada Limited.] reactor fuel channels. Three phases (α, β and ω) of zirconium are known to exist in Zr–2·5Nb alloy pressure tube materials. An as received pressure tube is composed mainly of α phase and approximately 8% β phase material. In the last step of production, the pressure tube is given a steam autoclave treatment (i.e. thermal aging at 400°C for 24 h). This treatment results in decomposing the β phase into an Nb enriched β phase and a metastable ω phase material. In the present experiment, as received pressure tube materials were modified by high temperature annealing and thermal aging treatments. This paper presents a neutron diffraction investigation into the phase compositions in the modified materials at room temperature using the C-2 high resolution neutron powder diffractometer at the Canadian Neutron Beam Centre.