On the two opposite ends of the pressure tube are end fittings. Inside the pressure tube are the fuel bundles, which generate heat and coolant from the Heat Transport System is used to remove this heat. On the outside of the pressure tube there is the calandria tube, separated from the pressure tube by multiple spacers. Within this gap there is a gas which is measured by an Annulus Gas System (AGS) which measures for moisture and also is a defense measure to ensure integrity of Pressure Tubes.
During regular operation, pressure tubes are exposed to heat, pressure and radiation. Like parts in a car’s engine, these components are tested, maintained and replaced over time. Given the role they play these activities are carried out using many methods.
Through extensive research, testing and modeling development, licensees have a thorough understanding of the impact of aging on pressure tubes. Bruce Power, in cooperation with other CANDU operators and the CANDU Owners Group (COG), has technical experts who are focused on reviewing and analyzing hundreds of data points to confirm the integrity of these components and defense in depth. This work ensures that the pressure tubes continue to meet the required safety margins and that pressure tubes are performing in a predictable manner.
The technical evaluations are updated following each outage and more frequently if new information is obtained from research or regular operational activities that would affect the conclusions of an existing evaluation.
After every inspection campaign, inspected pressure tubes are evaluated against compliance verification criteria to demonstrate that the tube will meet the established safety margins until at least the next planned inspection.