Pressure Tube Integrity

Simply put, Effective Full Power Hours on a nuclear reactor is like mileage on a car. Not all miles are equal. It depends on how you operate and maintain the car that determines its lifespan. If you maintain it well and drive it responsibly, the vehicle will last longer. Bruce Power takes great pride in maintaining our nuclear assets through meticulous operation, inspection, maintenance, repair, replacement and monitoring strategies that continue to evolve and improve with technology. Similar to a car, the EFPH calculations take into account when a reactor is at extremely low power (idling), operating at low power (city driving) or operating at full power (highway driving).

300,000 Effective Full Power Hours is written in an abbreviated form as 300 kEFPH. The k is a multiplier by 1,000.

Yes. Bruce Power’s modeling and data demonstrates safe operation to operate to a 300 kEFPH. The CNSC has already reviewed the application and has authorized operation of the Bruce A and B units up to 300 kEFPH in a decision made in 2018.  

The original design parameters and length of service for the operational lifespan of a Bruce reactor was a theoretical estimate that was done in the early 80’s before the units came online and started generating power. The estimated lifespan was based on conservative numbers and the best scientific projections at that time. In reality, the reactor components have performed far better than expected and the operational, inspection and metallurgical data supports that. Extensive data for each reactor is collected and updated continuously.

As mandated by the CNSC and part of our operation license, Bruce Power must continuously prove the reactors are safe to operate. Each unit has a planned outage that occurs every two years where extensive inspections and maintenance are performed. During planned outages, detailed measurements and inspections are performed in a sample group of pressure tubes that are selected and approved by the CNSC. The garter springs are located and if required, moved to a more desirable position to prevent contact between the pressure tube and calandria tube. Thin scrape samples of metal from inside of the tubes are sent away for analysis.

Detailed measurements and inspections of the tubes are also performed. Every four years, we are regulated by the CNSC to completely remove and replace one entire fuel channel assembly for extensive testing and end-to-end analysis is completed. Bruce Power collects detailed data on every fuel channel and component. If the data and results are not deemed adequate by the CNSC, the regulator can request more inspections and more data until they are fully satisfied with the results.

The MODAR tool is one of many tools deployed in outages at Bruce Power. It’s used specifically in Unit 8 and is a great example of a unit that would have been shut down if not for advanced tooling. Unit 8 was the last Bruce B unit constructed and came online May 22, 1987. Unit 8 was the first CANDU reactor to use tight fitting garter springs in the fuel channel assembly to help support the pressure tubes (PT) and maintain the gap or space between the PT and calandria tube (CT) to prevent premature degradation of the metal in the PT. During operation, the four spacer springs in each channel tend to gradually move outward towards the ends. The tool used to locate and adjust springs in all units built prior to Unit 8, is a tool known as Spacer Location and Relocation (SLAR). SLAR locates the position of the springs and if required, uses an electromagnetic pulse to move garter springs back toward the center into their desired position. The SLAR tool does not work on tight fitting garter springs. Close to a hundred million dollars and years of development was spent designing, building, and testing a new tool to move the tight-fitting garter springs using harmonics, or vibration. The Modal Detection and Relocation (MODAR) tool was first used in 2015, to shift the location of garter springs in Unit 8 fuel channels to prevent contact between the PT and CTs. It has been used in every Unit 8 planned outage campaign since then for data collection and the movement of springs to maintain safe operational parameters within the core of the reactor.

No, a pressure tube failure is part of the design basis for CANDU reactors, the CANDU design has defense-in-depth systems to maintain control and cooling of the reactor core and prevent any adverse impact on the public.  The barriers and systems that protect the reactor and the public from a radiological release include:

• The fuel bundle – The uranium pellets are stacked inside a zirconium sheathed pencil that’s approximately 1 foot in length. 37 pencils are assembled into a bundle format. That outer sheath of the pencil contains the uranium and the radioactive by-products from fission inside this first barrier.
• The pressure boundary system – The pressure boundary system contains the heavy water which flows around the fuel bundles and carries the heat generated up to the steam generators to boil light water which makes steam and turns the turbine generator. The pressure boundary system is considered a barrier as it contains these radioactive elements. Any components that are related to pressure boundary are subject to additional testing rigour and maintenance to ensure it’s integrity. Pressure boundary systems that are connected to the primary heat transport (PHT) or moderator systems are all within a containment structure.
• Negative Pressure Containment – all the reactor vaults, reactor fueling systems, auxiliary heavy water systems and anything connected to PHT or moderator water systems are housed within a protected envelope known as Negative Pressure Containment (NPC). This fortified system keeps any radioactive contamination within its boundaries and the air space inside is maintained at a lower air pressure to ensure any microscopic air incursions will draw clean air in, rather than allowing contamination to escape.
• Emergency Coolant Injection (ECI) – The fuel bundles in the reactor core must be cooled and must be underwater in order for the cooling to be effective. If a LOCA occurred, backup heavy water tanks can inject water into the core to maintain the water in the core. If the backup heavy water tanks were depleted, the ECI system can be triggered to inject cool light water into the core to maintain cooling. The water is collected in the basement of the vault and can be recirculated indefinitely.
• The Vacuum Building – The vacuum building is a large hollow concrete structure designed as the ultimate safety system in the event of a large loss of coolant accident due to a rupture of a feeder tube or main PHT header. In the unlikely event of a major LOCA, steam pressure would rise in the containment structure and the vacuum building would automatically be opened to draw in the steam and any contamination. If the vacuum building was triggered, that also trips a large dousing system of stored cooling water which reduces the heat, volume of steam, and contains the contamination inside the building. The vacuum building must be poised at all times during normal operation and if it is impaired for any reason, the entire station and all 4 units must be shut down if the restoration of this safety system cannot be resolved withing 48 hours.

No. The vacuum buildings have never been activated in emergency response. However, vacuum buildings must also be tested and maintained as per CNSC requirements on a 10-12 year cycle which requires the complete shut-down of all units in the power station.

Yes. Bruce Power has invested millions in the Bruce Units at both stations in response to Fukushima and extreme weather events. In summary, the modifications allow us to use alternate methods to plug in additional cooling, standby power, or filtration. The modifications give us much greater flexibility to cool, contain and control our reactor systems and protect the public in a direct hit of an extreme weather system that damages the existing operational infrastructure.