Bruce B reactors offline for planned check of vacuum safety system

Bruce Power has taken all four Bruce B reactors offline to perform scheduled work on the vacuum building CANDU safety system -a roughly once-a-decade requirement.

The outage began Tuesday, the start of a 20-day maintenance and inspection project, the nuclear operator said in a news release Wednesday.

The vacuum building is part of the containment system. Each reactor is in its own airtight vault with concrete walls of more than one metre thick. The reactor vault is maintained at a negative pressure and connected to a large cylindrical vacuum building.

“Maintained at one-tenth atmospheric pressure, the vacuum building is poised to suck up radioactive steam and contaminants in the unlikely event of a reactor accident. Once triggered, it douses the steam and contaminants with water from an overhead storage tank,” information from Bruce

Power says.

Vacuum buildings are unique to multi-unit CANDU generating stations and provide an additional protective barrier to the release of radioactivity to the environment, the company says.

“Bringing all of the station's operating units off-line at once is a large undertaking and our team has been planning for years to ensure it is completed safely,” said Adrian London, Bruce B's vice-president, in the release.

The work is being done this time of year because demand for electricity is lower. The grid will lose 15 per cent of available capacity due to the outage, Bruce Power said.

Last May, Bruce Power announced it won an international Top Innovative Practice Award for installing its new Containment Filtered Ventilation System, which had been added to the vacuum buildings at Bruce B and its companion generating station, Bruce A.

This “post-fukushima” improvement was recognized at the Nuclear Energy Institute's Nuclear Energy Assembly in Washington, DC. Bruce Power president and CEO Mike Rencheck described it as a “game changer” and a “first-of-its kind safety system.”

“Essentially this prevents the risk of a potential radiological release to the environment in the highly unlikely case of an accident,” a Bruce Power news release at the time quoted him saying.

A few days before the current Bruce B vacuum building work started, Unit 7 was taken offline April 18 for a two-month planned outage.

It ran for 646 consecutive days of operation, which is the eight-unit Bruce site's second longest, after Unit 1's post-refurbishment run of 694 days in 2020.

Unit 7 came online in 1986 and though originally scheduled to be shut down in 2015, Bruce Power says it has continued to operate reliably.

The current maintenance and inspection outage will ensure it's able to do so until its Major Component Replacement outage in 2028, the company says.

While offline the medical isotope cobalt 60 will be harvested from the reactors. Unit 7 has a unique isotope-production system that can produce many isotopes which can be harvested without shutting down the reactor. The other reactors must be shut down to harvest isotopes.

Unit 7 produces cobalt 60 and lutetium-177. Upgrades during the shutdown will increase production of lutetium-177, used in radiopharmaceutical cancer treatments, Bruce Power says.

Cobalt 60 is used to sterilize single-use medical devices, such as syringes, surgical masks, gowns and gloves, as well as in the specialized treatment of breast cancer and brain tumours.