Pressure tubes: The heart of the reactor

Inside all CANDU nuclear power reactors in Canada are several hundred fuel channels. Each fuel channel has one pressure tube, one calandria tube, end fittings and spacers.

Pressure tubes are the heart of the reactor. They are designed to contain the fuel bundles and the primary coolant (water) in a reactor.

During regular nuclear power plant operation, pressure tubes are exposed to high temperatures, high pressure and intense radiation, which can cause them to deteriorate. Much like with any machine, over time, nuclear reactor parts need to be tested, serviced and replaced.

The CNSC licenses nuclear power plant operators, who are required to regularly monitor the condition of pressure tubes to ensure they meet operational fitness standards. Key issues to watch for in pressure tubes are subtle changes in shape, state of material properties and appearance of flaws. These issues are monitored through periodic inspections and assessments by the licensee, followed by an independent review by the CNSC.

Although pressure tubes were deliberately designed to withstand operational wear and tear, they do age over time. And so, aging management programs for pressure tubes are essential to the ongoing safe operation of nuclear power plants.

Through extensive research, testing and modeling development, licensees must understand the impact of ageing on pressure tubes.

Licensees must perform inspections and demonstrate to the satisfaction of the CNSC that pressure tubes are able to continue to operate safely into the future.  Every two to three – years, inspections on pressure tubes are carried out. Inspection results are used by the licensees to conduct extensive modeling and prediction of the fitness for service of pressure tubes. Licensees must provide the CNSC with their periodic inspection plans.

The CNSC, as nuclear regulator in Canada, ensures comprehensive and rigorous oversight. CNSC staff analyse and evaluate the data provided by the licensee to confirm pressure tubes meet operational standards.

Inside each of CANDU nuclear power reactors in Canada are several hundred fuel channels. There are various parts that make up the fuel channel. 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. On the outside of the pressure tube there is the calandria tube separated from the pressure tube by multiple spacers.

Inside each of CANDU nuclear power reactors in Canada are several hundred fuel channels. There are various parts that make up the fuel channel. 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. On the outside of the pressure tube there is the calandria tube separated from the pressure tube by multiple spacers.

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