By Susanna McLeod
Special to Ontario Construction News
Plugging in a vacuum and putting clothes in the dryer, homeowners enjoyed the latest appliances, and businesses established energy-gulping facilities. Modern lifestyles strained electricity grids in the 1950s. Creating a clean, sustainable electricity supply, nuclear technology was developed and refined at Chalk River, at Rolphton, and at Douglas Point Generating Station. Ontario Hydro (now OPG) launched construction of its first large-scale nuclear power plant at Pickering in 1965.
The powerful Pickering Generating Station was commissioned in 1971. Electricity demand is again soaring and the 50-year old generating plant is a candidate for revitalization.
“Ontario Hydro chose to build nuclear stations with four reactors each, in order to reduce costs by sharing safety systems and other infrastructure,” said Appendix 2 of “Power for the Future Towards a Sustainable Electricity System for Ontario.” First on the schedule were Pickering A reactors and “in 1974, construction started on the four Pickering B reactors immediately beside Pickering A.” Federal and provincial governments provided most of the funding.
Safety was imperative for Atomic Energy of Canada Limited (AECL) when planning the construction in the urban region, about 5 kms east of Toronto’s metropolitan boundary. By constructing the million-kilowatt nuclear facility on Lake Ontario’s shore close to customers, the cost of transmission was lowered.
Assessments for the 140-acre property included potential earthquake forces, wind, and “snow load on a horizontal surface,” stated the Pickering Generating Station project report by Hydro Electric Power Commission of Ontario (HEPCO) and AECL in 1969. The sprawling plant had four reactor buildings, a powerhouse with a turbine hall and auxiliary bay, a service wing, and an administration building. “A single intake channel, screen house and gravity feed intake duct for condenser cooling water and process water serves all four units,” the project report described.
Condenser cooling water was returned to the lake at the westerly end of the facility.
Reinforced concrete with an elliptical dome formed each reactor building. The structures were built to withstand pressure after an accident of 6 psig (pounds per square in gauge—a pressure measured with respect to atmospheric pressure). The shielding concrete building stood 35.66 m tall plus a dome of almost 11 m. The walls measured about 1.22 m thickness surrounding the internal diameter of over 42.6 m. At the springline, the 60 cm dome thickness decreased to about 45 cm.
Supports for the reactor building base were constructed in a “system of about 750 steel piles which are driven to rock at about 40 feet below grade.” A circular slab of 1.52metre-thick reinforced concrete capped the piles and extended 1.22 m “beyond the perimeter wall.” The slab provided a robust base for “internal building structures and the external wall…”.
A vast complexity of water pipes, airlines, and cables ran through the secure buildings. Architects included safety procedures at every step. A glimpse at a few systems included emergency water storage tanks ready to spray for cooling any steam emitted into the vacuum building. It would cool the air of the same building “and thus suppress the pressure caused by temperature rise.”
Containing even the smallest leakage was crucial. Diaphragms, gaskets, flap valves and more ensured seals maintained their integrity. The reactor building was fitted with pairs of airlocks as part of the containment system. The airlocks had “double inflatable seals at the inner and outer doors.” Integrating a smaller personnel door into the larger entry, three door locks measuring about 2.43 m wide by 3 m high permitted movement of equipment, such as removal of fuelling machinery.
Components of the fuelling machine bridge mechanisms could be transported, along with “moderator heat exchanges, and a large shielding flask for removal of reactivity control elements.” Pneumatically-operated in sequence, pressing a pushbutton launched pressure equalization and unsealing of the doorway. The unbolting and opening of the door for entry then moved to the automatic closing sequence. In case of power failure, the process was also operated manually.
When Pickering A and Pickering B were completed, the “eight reactors shared common safety systems, including containment and vacuum, building, as well as the emergency core cooling system,” reported Appendix 2. However, this resulted “in a higher risk of accident than at other facilities.” Fortunately, the systems have operated safely and efficiently.
Construction costs for Pickering A’s four reactors rang up at $708 million, according to Appendix 2. Significantly higher, costs for completing the Pickering B project were estimated in 1974 to be $1.585 billion but “the final cost in 1986 was $3.846 billion.”
As Pickering began production, construction of another nuclear plant got underway—Bruce Generating Station.
Presently, six of Pickering’s CANDU® reactors (CANadian Deuterium Uranium) produce about 14% of Ontario’s electricity demand. As well, Pickering Nuclear Generating Station creates 20% of the world’s supply of Cobalt-60, a medical isotope used for diagnosis, radiation therapy and other procedures.
© 2022 Susanna McLeod. McLeod is a Kingston-based freelance writer who specializes in Canadian History.