The Canadian approach to reactor safety is about “defense in depth.” 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 are fitted with rapid shutdown systems that can stop the chain reaction within seconds. In addition, the station containment systems are designed to lock harmful radiation within the facility.
OPG’s nuclear stations are continuously monitored through a program of special testing and inspection of its components and safety systems.
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 in the vacuum building, the radioactive steam is condensed into liquid and contained.
At OPG's nuclear power stations safety is our first priority. In more than 40 years of operating our facilities, a member of the public has never been harmed from our nuclear operations. OPG’s priority for all of its generating stations, including its nuclear generation, is to safely operate our facilities in a manner that minimizes impact on the environment. All of OPG’s nuclear power stations are registered to the internationally recognized ISO 14001 standards for Environmental Management Systems. This voluntary standard directs our actions and demonstrates a high standard of environmental responsibility, including radiological safety.
Water safety and radiation
The lakes and groundwater around Durham’s nuclear stations are safe. In its operating history, OPG has never exceeded regulatory limits on radioactive releases into the environment, and typically releases are extremely small when compared to the regulatory limits.
Ontario’s regulatory limit for tritium drinking water levels is 7,000 Bequerels per litre (Bq/l). However, OPG has set its own internal target much lower, at just 100 Bq/l. In 2006, water tested at the closest municipal water treatment plants to our stations measured between five to seven Bq/l -- a trace amount. In fact, OPG takes samples daily at local municipal water treatment plants and the results are consistently below our internal target of 100 Bq/l.
Radiation in our environment
All Canadians are exposed to naturally occurring radiation, mostly from the sun and from radon that is found in soil as well as manmade sources such as X-rays.
Exposure to radiation in humans is measured in microsieverts. A microsievert is a measurement of radiation dose by an individual. The average exposure of Canadians is 1,770 microsieverts a year. In 2006, living near one of OPG’s nuclear plants in Durham Region added less than three additional microsieverts (1.1 microsieverts at Darlington, 2.8 microsieverts at Pickering) to this amount over the course of the year. By contrast, the food and water we consume each year accounts for approximately 300 microsieverts. Other sources of radiation include:
Cosmic rays: 300 microsieverts
Ground: 230 microsieverts
Dental X-ray: 100 microsieverts
Flight to Vancouver: 40 microsieverts
OPG, Emergency Management Ontario, and regional and local governments all work together to protect the public. Each organization has responsibility for a distinct area of the emergency response, and our emergency response personnel are available 24/7 to respond to an emergency. OPG’s robust training schedule ensures that our responses to emergency scenarios are tested on a regular basis and include a successful test of our response to an earthquake scenario.
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 emergency power generators are seismically qualified and have sufficient supply of fuel to enable restoration of an alternate source of power to the site, or the procurement of additional fuel. In addition to the seismically qualified emergency power generators, each site also has standby generators. These standby generators are built and maintained to high standards and depending on the magnitude of the earthquake, there is a reasonable probability some of them will survive a seismic event, or could be made available shortly after a seismic event. 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.
Following the event in 2003, OPG installed an Auxiliary Power System at Pickering consisting of two auxiliary power generators to enable the rapid restoration of site power following a loss of the electrical grid. In addition, in 2010, we installed a third seismically qualified EPG to enable the overhauls to the existing two EPGs.
Over the last several years OPG has invested in upgrades to these systems and our fire suppression systems.
How it works
Find out how a nuclear reactor produces heat to convert water into steam, which spins a turbine or generator to make electricity.