Bruce Power’s Number 1 value has always been ‘Safety First.’ We operate all our units based on this value, and the results of our regular testing program must be conclusive that the fuel channels are safe to operate at all times.
Inside the CANDU reactors at Bruce Power, there are 480 fuel channels. Each fuel channel consists of a pressure tube, a calandria tube, end fittings and spacers.
On the two opposite ends of the pressure tube are end fittings. Inside the pressure tube are the fuel bundles, which generate heat. On the outside of the pressure tube there is the calandria tube, separated from the pressure tube by multiple spacers.
The Canadian Nuclear Safety Commission (CNSC) licenses nuclear power plant operators, which are required to regularly monitor the condition of pressure tubes to ensure they meet operational fitness standards.
This video describes the function of the fuel channels and pressure tubes, how we test and maintain them, and a description of our innovative Bruce Reactor Inspection Maintenance System (BRIMS) and the tools it delivers to the reactor face.
Fuel Channel Assembly
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.
How inspections are carried out
During planned maintenance outages, CANDU reactors all undergo routine testing of fuel channels to test for fitness for duty and safety, measuring factors such as pressure tube and calandria tube changes and elongation; review of fracture protection; in-service considerations; and pressure tube to calandria tube separation.
Bruce Power and its partners developed a first-of-a-kind tool that has revolutionized how we conduct this testing. The Bruce Reactor Inspection and Maintenance System (BRIMS) machine is used to deliver our various inspection tools to the reactor face and deploy them into the fuel channels.
Each tool delivered by the BRIMS system is designed to conduct specific and thorough inspections of the fuel channels and pressure tubes. These tools include:
Pressure Tube tools
All of these tools give us a very clear picture of the health of the pressure tubes in our units by providing extremely accurate measurements and data. This large amount of data is also used by Bruce Power technical experts to ensure the integrity of the pressure tubes to achieve safety margins the units continue to operate in a safe and predictable manner.
ANDE – The BRIMS Advanced Non-Destructive Examination (ANDE) tooling system performs ultrasonic inspection in a wet, defueled channel. It takes seven to eight hours to process each channel. This ultrasonic testing measures for flaws, channel diameter, wall thickness, sag, and pressure tube to calandria tube gap, and also locates garter springs. Fundamentally, this is used to verify physical integrity of the tube.
CWEST – The Circumferential Wet Scrape Tool (CWEST) is used to obtain fuel channel metal samples to determine Hydrogen levels inherent in the metal. These metal samples, or scrapes, are taken from various points in the pressure tubes. Fundamentally, this measures hydrogen concentration.
SLAR & MODAR – The Spacer Location and Repositioning Tool (SLAR) and Modal Detection and Reposition (MODAR) detects and repositions garter springs in a wet, de-fueled channel. This ensures adequate separation between calandria and pressure tubes.