“Defence in depth” is the Canadian approach to reactor safety. This means providing multiple technological and operational safety measures that act first to lessen the chance of an accident and then, if an accident does take place, reduce the possibility of harmful effects on employees and the public.
Each of OPG’s nuclear stations is fitted with rapid shutdown systems that can stop the chain reaction within seconds. The safety systems are independent from the rest of the plant, and each key safety component has three backups. The station containment systems are also designed to lock harmful radiation within the facility.
The containment system surrounding a nuclear reactor is designed to prevent the release of any radioactive material to the outside environment in the unlikely event of an accident. The containment system at OPG’s nuclear stations consists of an airtight reactor containment building (with reinforced concrete walls up to 1.8 metres thick) for each reactor.
At Pickering and Darlington nuclear stations, each reactor building is connected to a common vacuum building, which assumes the containment function. This building works as a vacuum cleaner. In the event of a release of radioactive steam into the reactor building, this steam would be vented to the vacuum building and prevented from escaping into the environment. Once inside the vacuum building, the radioactive steam is condensed into liquid and contained.
Emergency backup power supply
Ontario’s CANDU reactors have considerable redundancy in back-up power supplies. Across OPG’s nuclear fleet there is a mix of standby generators, emergency power generators (EPG), and auxiliary generators with varying degrees of seismic qualification (back up to the back up).
In the event of an earthquake or other worse-case scenarios, OPG’s nuclear emergency power system is designed to provide electrical power to certain nuclear safety-related systems that support the capability to control reactor power, cool the fuel and contain radioactive fission products. There is also a passive cooling system in place.
OPG’s nuclear sites are equipped with emergency power generators and standby generators. All are seismically qualified and have a sufficient supply of fuel to enable restoration of an alternate source of power to the site. At Darlington, there are four standby generators, only one of which is required to support the site. At Pickering, there are three standby generators for each unit pair, only one of which is required for each unit pair. Over the last several years OPG has invested in upgrades to these systems and our fire suppression systems.