The Pickering Nuclear Station has a long history of operational problems, accidents and poor performance.

Interview with Dr. Frank Greening, retired nuclear researcher on why the Pickering Nuclear Plant presents serious safety concerns.

The four Pickering “A” reactors are the oldest commercial reactors in the country (and some of the oldest in the world), and began commercial operation between 1971 and 1973. The four Pickering “B” reactors were added on between 1983 and 1986.  

The Pickering nuclear station has a greater risk of accident than other stations because the containment system’s vacuum building is shared between six operating reactors. The Pickering A reactors also lack two completely separate shutdown systems, the norm for modern nuclear plants. As a review by world-recognized nuclear expert Arnold Gunderson stated, “At the Pickering site, there is only one overall safety related containment system when there should be six separate safety related containment systems. This design flaw has created a cumulative risk at the Pickering station that is higher than that at any single unit station in Canada.” Gunderson notes that, in particular, this design flaw makes the eight-reactor plant particularly at risk for the kind of cascading accident seen at Fukushima, where damage to one reactor led to fires and explosions that damaged adjacent reactors.

Here’s a brief summary of some of the plant’s problem-plagued history:

Excerpt from The Standing Senate Committee On Energy, The Environment And Natural Resources report Canada’s Nuclear Reactors: How Much Safety Is Enough?

Throughout its operation, Ontario Hydro reported other significant events at the Pickering station to the AECB. Among them were the following:

On August 1, 1983, Pickering reactor 2 had a loss of coolant accident after a pressure tube suffered a metre-long rupture. The station was shut down and the four reactors at Pickering A were eventually retubed at a cost of about $1 billion. 

On November 22, 1988, an operator error damaged 36 fuel bundles. The cooling system was contaminated by radioactive iodine that was vented into the environment over several weeks following the accident.

 On September 25, 1990, Pickering reactor 2 experienced large power shifts in the reactor core. Staff spent two days trying to stabilize it before shutting it down. The AECB later criticized the utility for not shutting down immediately.

On August 2, 1992, Pickering reactor 1 had a heavy water leak from a heat exchanger that resulted in a release of 50 trillion becquerels of radioactive tritium into Lake Ontario.

In 1994, Pickering A was the site of Canada’s worst accident at a commercial nuclear station. On December 10, 1994, a pipe break at Pickering reactor 2 resulted in a major loss of coolant accident and a spill of 185 tonnes of heavy water. The Emergency Core Cooling System was used to prevent a meltdown. About 200 workers were involved in the cleanup. The reactor was restarted 14 months later. [More on why this incident could have led to major radiation releases due to a fundamental design flaw in Candu reactors.]

On April 15, 1996, Pickering reactor 4 had a heavy water leak from a heat exchanger that resulted in a release of 50 trillion becquerels of tritium into Lake Ontario.

More recently, the station has continued to experience problems:

In July 2007, OPG was heavily criticized for failing to act promptly to fix a leak in Pickering’s radiation containment system. Observers speculated that OPG might be failing to act promptly because the repair could require shutting down all four reactors in the Pickering A plant, due to the plant’s unusual (and unsafe) reliance on a single shared containment system.

In March 2011, there was a leak of 73,000 litres of demineralized water into Lake Ontario at the Pickering A nuclear generating station. While contending that there was no risk to the public, OPG acknowledges that this kind of leak was not acceptable, especially considering the Great Lakes are the source of drinking water for millions of people.

In 2011 as well, 11 employees at the Pickering Nuclear Plant were fired over evidence of drug use. Eight of the workers were eventually re-instated.

On March 25, 2011 Pickering Nuclear experienced a brief partial loss of power on its Unit 1 reactor, while performing start up activities.

In March 2011, OPG staff discovered a failing pump seal had been leaking moderator water containing tritium in the Unit 4 moderator room.

On Oct. 11, 2012, the Pickering Nuclear had a spill of approximately 400 litres of moderator water and an OPG employee was exposed to radiation.

On June 5, 2012, “a number condenser cleaning balls were inadvertently discharged into Lake Ontario from the Pickering Nuclear station.”

On the night of Jan. 1, 2013, a fire broke out in a lube oil purification system in the Pickering Nuclear Unit 1 turbine hall.

On Jan. 14, 2014, “approximately 200 kg of heavy water was released onto the floor of the Unit 4 reactor building at the Pickering station during the transfer of liquid between two tanks.

On April 29, 2014,  “Operators at the Pickering station made the conservative decision to shut down the reactor in order to investigate the cause of instrumentation fluctuations for reactor moderator system on Unit 1.

In June 2014, the Pickering plant once again leaked demineralized water “with a trace of hydrazine” into Lake Ontario.

In November 2014 there was a leak of heavy water inside a containment building when a valve was unintentionally opened during maintenance. 

In July 2015, staff at Pickering discovered ” incorrect blocking and locking of a valve that is part of the guaranteed shutdown system.”

In September 2015, an unexpected “system trip” led to the sudden shutdown of a reactor at Pickering, leaving the province scrambling to import replacement power. The trip came at a particularly difficult time as a number of the province’s other reactors were also shutdown at the time for repairs.


A review of the Pickering Station’s risks by a U.S. nuclear engineer identified a number of problems, including:

  • Shared containment building for multiple reactors, greatly increasing the odds of cascading failures
  • An overly complex design with miles of piping prone to leaks 
  • Significant risk identified by OPG itself of a steam generator failure that could lead to a major radioactivity release
  • Foundations and other concrete weakened by 45 years of Canadian winters and freeze-thaw cycles. At a U.S. plant 15 years younger than Pickering, concrete was found to have weakened by 25%.
  • A serious design flaw that causes the reactor core to power up when there is a loss of coolant accident, a perfect recipe for a meltdown.

As the author notes, “Quite simply, nuclear plants like those at Pickering should not be allowed to operate based upon mysterious unfounded calculations or operating confidence levels as low as 70%. While both OPG and CNSC claim that extending the life of the Pickering Nuclear Generating Station is based upon hard data and pure scientific analysis, it appears that there is a considerable amount of guesswork underlying each
organization’s calculations.”


Efforts to re-build reactors at Pickering went so massively over budget that two reactors were eventually simply mothballed.  The rebuilt reactors have performed poorly.