Material Surveillance of CANDU Zirconium 2.5%Wt Niobium Pressure Tubes

There are 26 operating CANDU nuclear power plants, varying in size from 540 to 880 MW(e). The majority (18) of these plants are located in Canada, with others located in Argentina, Korea, China, and Romania. These plants entered commercial service at various times between 1971 and 2003. As such, some of the plants are more than 30 years old. In addition, there are new plants under construction and some older plants under refurbishment. Each plant contains between 380 and 480 fuel channels, for a total of almost 11,000 fuel channels currently in-service. A fuel channel is comprised a Zr-2.5%Nb pressure tube, stainless steel endfittings, a zircaloy-2 calandria tube, and a series of annulus spacers (Figure 1). The pressure tube serves to: i) Support and locate the nuclear fuel bundles, ii) Form part of the pressure boundary of the heavy water coolant system, and iii) Provide an additional boundary between the nuclear fuel and the external environment.