Evaluation of Zircaloy-2 Pressure Tubes from NPD

Abstract

The pressure tubes of Canadian Deuterium Uranium (CANDU) reactors are monitored to evaluate their health. The main factors that affect their service life are changes in dimensions, shape, mechanical properties, and flaw tolerance. We have developed equip-ment and techniques to measure these properties and assess the health of the tubes. In this paper we describe the examination of the Zircaloy-2 pressure tubes of the Nuclear Power Demonstration (NPD) reactor. Their dimensional changes posed no problems. However, the combined effect of irradiation and the presence of radial hydrides caused the fracture toughness to decrease to such an extent that it would be difficult to assure leak-before-break in the future. Thus the reactor was closed down after 25 years of operation.

Bioinertness and fracture toughness evaluation of the monoclinic zirconia surface film of Oxinium™ femoral head by Raman and cathodoluminescence spectroscopy

“…This means that, if the substrate is highly tough and compliant, the crack will arrest at the interface and will remain confined into limited surface regions. The substrate of Oxinium™ femoral head components is a quite ductile Zr-2.5%Nb alloy and its fracture toughness can be estimated in the order of 75-96 MPa  m 1/2 (Coleman et al, 1989;Walker, 1972;Wallace et al, 1989), which is comparable with that of steel (Roy et al, 2008), and an order-of-magnitude higher than that of the surface oxide fracture toughness and of that of any bulk ceramic used in biomaterial implants. Therefore, any crack, occasionally formed as a consequence of extrinsic factors, on the Oxinium™ surface not only will remain confined in its depth within the oxide film but will also hardly spread through the surface of the oxide film, which proves the extremely high structural reliability of the Oxinium™ joint components in comparison with bulk zirconia ceramic components.…”

Hydride-Related Degradation of SNF Cladding Under Repository Conditions

“…The key aspects of DHC initiation in CANDU pressure tubes can be divided into several processes, i.e., sagging of the hot pressure tube (maintained in a horizontal position at =3OO0C), contact of the pressure tube OD with the horizontal cold calandria tube (temperature =70°C), hydrogen migration to the cold contact spot, nucleation of a hydride blister, growth of the hydride blister, crack initiation in the blister, crack growth in the blister, and adjacent metal. Qualitatively, these processes are understood fairly well (Chow and Simpson 1986;Coleman et al 1989;Cheadle et al 1987;Moan et al 1990;Shi and Puls 1996).…”

“…Crack initiation in failed CANDU pressure tubes occurred, in fact, not in association with fabrication-related flaws but in association with hydride blisters that formed during operation on the OD side of the tube (Chow and Simpson 1986;Cheadle et al 1987;Leger et al 1989;Coleman et al 1989;Moan et al 1990). That is, microstructural evolution which occurred on the OD side surface over a period of =lo-20 years was the key in crack nucleation in the failure CANDU pressure tubes.…”