Pickering (Canada)

Map of Pickering

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Pickering-A (units 1-4) and Pickering-B (units 5-8): 8 * 500 MW (PHWR) Candu units, constructed by AECL;
Pickering-A units 1-4 were shut down in 1997, unit 4 was reconnected to the grid in 2003, unit 1in 2005.

Facilities in Pickering

plantreactor typconstruction startoperation startshut down
Pickering-1CANDU 500 (PHWR)19661971
Pickering-2CANDU 500 (PHWR)196619711997
Pickering-3CANDU 500 (PHWR)196719721997
Pickering-4CANDU 500 (PHWR)19681973
Pickering-5CANDU 500 (PHWR)19741982
Pickering-6CANDU 500 (PHWR)19751983
Pickering-7CANDU 500 (PHWR)19761984
Pickering-8CANDU 500 (PHWR)19761986

Pickering-1 was put back in commercial operation after it had been shut down in 1997.
In the past years the unit has been extensively backfitted:
The Moderator System has been refurbished, four out of 780 feeder tubes were replaced, the Heat Transport System Pressurization was extensively overhauled.
These measurement cost $1016 million.


Unit 4 was connected back to the grid after six years of shut down and backfitting work. The fire detection, protection and prevention has been improved, resistance to earthquakes has been enhanced, standby generators and condensers have been refurbished and replaced to meet with higher environmental standards, and an extensive program of training for all employees has been completed.


The Pickering town council called last week for a full public review of the quarter-century-old facility under a newly enacted Environmental Bill of Rights by both federal and Ontario authorities, asking the provincial government specifically to probe the station's heavy-metals discharges into Lake Ontario.
Professor Donald Mackay asserted three weeks ago that some 60 tons of copper and a lesser amount of zinc from eroding brass steam condenser pipes were being discharged annually into Lake Ontario at the Pickering site. More than a 1.000 tons of these heavy metals have been dumped into the lake in the past 25 years. "They never go away, they're toxic and they tend to bio-accumulate in fish," Mackay said.
The copper/zinc emissions from erosion of brass piping that carries the lake water into and out of turbine condensers was first identified at Pickering in 1989. Replacing the brass tubes with titanium tubing began in 1994 and will be completed in the four newer Pickering-B units by this fall. Condenser tubing in the four older Pickering-A unites will be replaced with stainless steel to "reduce emissions to essentially zero" by 2000.


Ontario Hydro´s unprecedented decision to shut down all eight units at the Pickering nuclear station to replace a single component that serves all units in a loss-of-coolant accident (LOCA) has led to heated debate among Canadian politicians, environmentalists, and a Hydro union representative over the station's safety.
Hydro´s decided April 20 to shut down the eight units while replacing a faulty check valve in the emergency coolant injection system (ECIS) came just days after station management reported a 1.000-liter leak of tritium-tainted cooling water.
That April 16 incident occurred while unit 4 was shut down for maintenance. A heat exchanger condenser in the service water system sprang a leak. Tritium detectors caught the leak and it was isolated after the 1.000 liters got in to Lake Ontario. The heavy water's activity measured 800 Bq/l; Canadian regulations limit emissions to 7.000 Bq/l.
The Atomic Energy Control Board (AECB) has already approved the Pickering units´ restart and Hydro plans to start bringing units back on line May 4 or 5. Units 6,5,1 and 7 are to resume operations, in that order. Pickering-4 will remain down for more than a month for scheduled maintenance and the other three will be returned to operation following a "status review".
The valve failure that triggered the unprecedented closure was caused by a faulty mechanism attached to the clapper (closer device) which was designed to indicate the clapper position. That mechanism jammed so, with AECB approval, that it was removed.


Spill of about 170 liters of heavy water during transfer of heavy water from the moderator purification system to resin storage tanks. Emissions from the site < 1% of annual limit, according to the director.

Loss of Coolant Accident :
Resulted in the use of the emergency coolant injection system, for the first time ever at a CANDU reactor. Initially, a relief valve in the reactor core cooling system stuck open, allowing cooling water to enter the bleed condenser (an overflow tank for the cooling system). Following automatic shutdown of the reactor, pressure increased in the cooling system, causing bleed condenser pressure relief valves to open. The piping to one of these valves cracked because of severe pipe vibration, spilling cooling water into the reactor building. A total of 185 tonnes of water were spilled.

The ECCS pumped about 140 tonnes of water into the core over several hours to prevent overheating and melting of the fuel. Workers stopped the leak after 1 1/2 hours by manually closing all liquid relief valves on the core cooling system. About 200 workers were involved in the clean-up effort.
Radioactivity was released to the environment following the accident at levels comparable to a normally operating station, even though all four reactors were shut down pending the investigation and design changes. For example, during January, Pickering "A" radioactive emissions included 600 GBq of tritium to air and 37 TBq of tritium to Lake Ontario. It is estimated by Ontario Hydro that Pickering- 2 will be out-of-service until October 1995, since biennial maintenance work planned for this fall was rescheduled to overlap with the investigation of the accident.

The same design flaws that caused the Pickering accident exist at other CANDU reactors. A similar
but less severe accident happened at Bruce - 5 only a few months later, despite a detailed analysis by Ontario Hydro following the Pickering accident. In both accidents, super- heated, radioactive cooling water leaked from the reactor core because of faulty valves. LOCAs can result in overheating and melting of reactor fuel and large releases of radioactivity from the station. In both of these accidents and a third similar accident at Wolsung- 1 in South Korea, damage to the fuel bundles was apparently avoided.
The cost for repairs and retrofits at the four Pickering "A" reactors is currently estimated to be $10.5 million.

The Atomic Energy Control Board established an Investigation Team to review the accident circumstances. The AECB Investigation Team
determined that some actions taken by reactor operators (as instructed through the Power Reduction Action Guide) actually contributed to the accident. In addition, stopping the leak by closing all the pressure relief valves meant there was no overpressure protection for the entire primary cooling system, and this was done without regulatory approval. According to the Team, Ontario Hydro's Root Cause Analysis is incomplete. The Investigation Team made a number of recommendations to Ontario Hydro including: revision of reactor operating procedures; audit of the human performance evaluation system; and review of nuclear
emergency procedures to make the Ontario Hydro plans consistent with the province's nuclear emergency plan. The Team also recommended that the AECB develop and implement an emergency response plan and establish a system for reviewing safety reports, accident reports and operating procedures in a timely way. The Team concluded that in-depth inspections are needed at
nuclear stations, in addition to the usual compliance inspections done by the AECB staff, and that the process for reviewing operating procedures must be examined, since the instructions followed by the operators contributed to the accident in this case.

The root cause of these recent accidents has been traced to failure of a diaphragm in a liquid relief valve of the reactor core cooling systems. The secondary accident stage involved damage to the bleed condenser relief valves, and in the case of Pickering, the piping as well. The review concluded that design of the bleed condenser pressure relief system is inherently flawed in CANDU reactors. AECB staff have recommended design changes for each nuclear station in Canada with the exception of Pickering. Pickering "A" had design
changes made since the December accident. Pickering "B" reactors apparently have different bleed condenser piping arrangements that won't lead to this type of accident. AECB staff noted that
the analysis carried out by Ontario Hydro Nuclear at Bruce "B" prior to the May accident failed to identify the possibility of the very situation that did arise.
Ontario Hydro is considering design changes at Darlington and Bruce to prevent repeats of the accidents. Reactors at Gentilly 2 in Quebec and Point Lepreau in New Brunswick also share the
design flaws.
In reviewing information from the AECB and Ontario Hydro about the two recent accidents, Nuclear Awareness Project researcher, Irene Kock, noted:
"Ontario Hydro has tried to downplay the similarities between the Pickering and Bruce spills. However, all the Darlington and Bruce reactors share the same design flaw. Ontario Hydro should not beallowed to operate nuclear stations with known design flaws."

"At some point we have to stop sinking money into reactor repairs and retrofits. The phase-out of older reactors would save money and reduce the risk of a catastrophic accident."

Unit-1 and 2 were restarted in June 1995


Heavy water leak shut down the reactor just 2 weeks after preoperational testing. The unit has been down since June 1989 for replacement of all fuel channels. The leak was caused by a ruptured valve seal. 12.500 liters of heavy water leaked into the heat exchanger chamber within the confinement during a two-hour period before the valve was repacked. The heavy water was recollected.


Large power vibrations ( increasing!) but operators did not shutdown the unit. Fluctuations were caused by the core configuration. The power variation was growing. Utility managers said, that sooner or later would have triggered a scram.


A maintenance crew mistook a rehearsal dummy for a shielding device during removal of a Co-60 rod from a control channel. Co-59 rods are irradiated in a selected number of control channels to produce Co-60 for medical and industrial applications. The three man recieved radiation doses of 2.2, 9.2 and 12,7 rem respectively !! (one of them received a 74 rem skin exposure!)


Power excursion that caused fuel failures; resulted in several improvements and risk assessments of 34 seperate systems.