Neutron Irradiation and Cold Work Effects on Zircaloy-2 Corrosion and Hydrogen Pickup

Abstract

Nearly 200 pre-autoclaved and weighed coupons of reactor-grade Zircaloy-2 in the annealed, 10, 20, and 40 per cent cold-worked condition have been exposed to the fast neutron flux of the Engineering Test Reactor (ETR) in nominal 540 F pH 10 water for up to 125 days. Flux intensity varied from 0.17 to 1.04 × 1014 nv (>1 Mev), and integrated neutron exposures ranged from 0.3 to 8.2 × 1020 nvt. Comparisons of weight gain and hydrogen pickup results among irradiated specimens and with unirradiated control coupons were used to broaden the area of present knowledge relative to the combined effects of neutron irradiation and cold work on surface chemical reactions and hydrogen absorption in Zircaloy-2. In general, exposure to the in-core coolant environment of the ETR causes an order-of-magnitude increase in average corrosion rates, similar to the effect of superheated steam at a temperature approximately 200 F above the irradiation temperature. In-reactor weight-gain data exhibit an apparent saturation effect with increasing flux intensity, and measured weight gains have been confirmed by optical measurements of oxide film thickness. Direct visual observations and photography at magnifications up to 40 × of irradiated coupons oxidized to weight gains as high as 150 mg/dm2 showed the surfaces to be smooth, glossy, and dark gray or blue-black in color. Some of the coupons appeared to be streak stained, but there were no indications of blistering, spalling, or light-colored oxide even at sharp edges and corners. No significant or consistent variation of weight gain with cold work has been found for material exposed in- or out-of-reactor. No significant effect of flux intensity or integrated flux on hydrogen sorption was observed.