Darlington Nuclear Generating Station

The plant began construction in September 1981 and planned to start initial operations in 1985. Several delays ensued, and the construction start on Units 3 and 4 was put off until 1984 and 1985. Unit 2 entered operation in 1990, followed by Unit 1 in 1992, and Units 3 and 4 in 1993. The delays and resulting cost overruns have made Darlington a primary case study for the anti-nuclear movement in Canada, and was one of the main reasons Ontario Hydro was broken up in 1999 and its debts paid off by special billings. After initial operations and shakeout, it is often among the most reliable plants in the world in terms of capacity factor. The plant completed a mid-life upgrade in February 2026.

Room for a second four-reactor unit had been in place since the original site selection, with a large area to the east of the current plant set aside for what was known as Darlington B. In 2006, Ontario Power Generation began the process of applying to build a two-unit plant on the B site. This project was cancelled in 2013 when the estimated cost was far beyond initial projections. In 2020 plans started to install a much smaller BWRX-300 small modular reactor on the B site, which are ongoing as of 2023. This "Darlington New Nuclear Project" was identified as a priority project by Canadian Prime Minister Mark Carney in September 2025.

History

Planning, controversy and delays

Darlington was part of a large nuclear buildout planned by Ontario Hydro based on their predictions of almost linear growth in power demand at 7% per year essentially forever. Based on this predicted growth, the company stated that nuclear would account for 60 to 70% of the province's supply by 1990, and for that to occur, a large number of new reactors would have to be built. Land at the Darlington Provincial Park was identified as a potential site in the late 1960s, and Hydro purchased the plot in 1971 as an "energy centre". The first official plans to develop the site for nuclear were approved in 1973, apparently at the personal direction of Conservative Ontario premier Bill Davis without discussion by cabinet. At the time, the construction cost of the four-unit plant was estimated at $4.5 billion (equivalent to $31 billion in 2025), and construction would start in 1979. Public hearings began in 1974 and the general plans were finalized in 1976. The official go-ahead from the government was given on 18 April 1977, and the first contracts for construction let on 8 June 1978.

Through the rest of the 1970s, Hydro's future demand estimates were repeatedly attacked as unrealistic. The 1973 oil crisis and subsequent 1973–1975 recession led to greatly reduced growth rates, which reached zero in the province in 1977. As these concerns became more public, in 1975 Davis formed two independent committees, the Porter Commission and the Select Committee, both of whom concluded the predictions were far too high. Shortly after, the recently formed Ministry of Energy and the public Energy Probe foundation both released reports stating that the company's predictions for power use in 2000 were some 12 gigawatts too high, about three Darlingtons. In 1980, the Porter Commission delivered its final report, which stated the growth rate would be closer to 4% and suggested Hydro should abandon its plans for further nuclear plants and should instead develop smaller plants and implement demand management. This advice was pointedly ignored.

Construction starts, and pauses

The ongoing expansion plan was paid for by debt financing primarily through the sale of commercial bonds. Given the public scrutiny and generally negative reports, in 1976 Energy Minister Darcy McKeough told Hydro to slow down its demands and spread out the budget or the province would not guarantee the company's bonds. Darlington was one of several major programs for that time frame, including major expansions at Pickering and Bruce. Hydro responded by pushing back the construction start to 1981, with the first reactor coming online in 1985 and then the other three after that, one every 12 months. This pushed the budget up only slightly to $3.9 billion in construction and another $1 billion for heavy water. A more detailed budget, this time accounting for inflation during the expected construction period through 1988 put the final figure at $7.4 billion, equivalent to $31 in 2025. The time-frame was deferred and advanced several times over the next few years.

In 1981, Hydro finally responded to the concerns about overbuilding with a new prediction of 38 gigawatts demand in 2000, a full 52 gigawatts less than their predictions made in 1978. A 1984 report puts the future growth at 3% at least until 1992, which, along with high interest rates of the era, led the company to cancel any future buildout for this period. Even the post-1992 demand seemed uncertain and no new reactors were scheduled. The company turned its attention to grid improvements.

Construction began on schedule, with the "first pour" in June 1981. In 1982, the construction starts for Units 3 and 4 were pushed back several years to 1985. In 1983, suffering from overcommitment and understaffing, Hydro management ordered the project be delayed. The engineering staff on Darlington were assigned to other projects, including the expansions at Pickering and Bruce that were now about to come online. At the time, Hydro calculated the budget to have risen to $10.9 billion. The pause ended in early 1985, but not all of the original staff were assigned back to the project, and new staff had to be hired and trained. Additionally, during the pause a number of issues in the design were found, this being the first plant of the ~900 MW size to be built, introducing further delay in getting construction started again. At this time, the company had already spent the original $7 billion budget, and was now predicting another $4 billion would be needed to complete it. Completion of Unit 2 was now predicted to be in 1988.

Reexamination, go-ahead

On 2 May 1985, the 1985 Ontario general election resulted in the ruling Conservatives receiving a minority government, but a vote of no confidence in June ended their 42-year rule and brought David Peterson's Liberals to power with support by Bob Rae's NDP. Peterson had previously voiced his support for an immediate stop to Darlington. Rae relied on the support of the Hydro worker's union, CUPE Local 1000, who strongly supported the project. As part of the inter-party deal, Peterson promised to not stop construction while a new commission considered the issue.

The Select Committee was reformed and produced a new report in 1986. By this time the Chernobyl disaster had cast a further pall over the field, and Hydro had further reduced its predictions to 30 GW in 2000. The committee provisionally accepted the continuing construction of Darlington Units 1 and 2, but suggested a wait-and-see period before allowing completion of Units 3 and 4. It was during this period that the labour force at the site reached its peak of 7,000, making it the largest construction program in North America at that time. Cabinet approved the continued construction in 1987, before the next election.

Now seven years into a four-year building schedule, during a period of high interest rates, the budget continued to balloon. An additional $3.3 billion can be attributed to the interest during these delays. An additional $1.2 billion had to be added to the bill as Hydro changed their accounting procedures and moved several items, including training the operators, from operational costs to capital. Design changes due to changing safety requirements after the Three Mile Island accident and Chernobyl added a further $0.9 billion, and other unforeseen changes to construction, including site works, added another $1 billion. As a result, the final cost was put at $13.8 billion, a full $6.8 billion, or 86%, over the 1981 estimate.

Commissioning and initial operations

Unit 2 was the first to start construction on 1 September 1981. Unit 1 followed on 1 April 1982. Construction started on Unit 3 on 1 September 1984, and Unit 4 on 1 July 1985. Construction on 1 and 2 continued with the pauses noted above, but 3 and 4 were significantly scaled back. Unit 2 entered commercial service on 9 October 1990, and Unit 1 on 14 November 1992. The final two units were much closer to competition by this point, with Unit 3 entering service on 14 February 1993, and Unit 4 shortly after on 14 June.

Almost immediately on entering service, the power shafts on Unit 2 connecting the steam turbines to the alternators were found to suffer from cracking, which led to lengthy shutdowns in 1990 and 1991. This was addressed with a new shaft design installed in May 1992. The other three units had already received the original design, but for initial operations they were modified to avoid the problem while awaiting the new shafts, expected in May 1993 for Unit 1 and in March and August 1994 for Units 3 and 4. In early 1991 it was found that vibrations in the fuel assemblies in Unit 2 was causing them to become damaged. This was ultimately traced to a problem in the pumping system that injected a 150 Hz pressure fluctuation. Changing the impellers to increase the rate to 210 Hz solved the problem.

As a result of these issues, the initial availability, or capacity factor was low. During its first three and a half years of operation, Unit 2 achieved a lifetime load factor of only 29.9% while Unit 1, between July 1992 and the end of June 1993, achieved a load factor of 56.8%. The changes, especially the new power shafts, also added another $600 million to the final bill.

Breakup of Hydro

The Peterson government fell in 1990, resulting in Rae's NDP taking the province in the midst of a recession. The Darlington plant was still under construction, and still as politically radioactive as it had been through the 1980s. Rae made the decision to complete the plant, but to ensure that these sorts of overruns did not occur again, he appointed Maurice Strong, former CEO of Petro-Canada, to become CEO of Hydro and shake up the company. Strong asked Bill Farlinger, a laissez-faire market-economy advocate, to suggest ways to reform the company. As a result of Farlinger's suggestions, Strong began the process of breaking up the company into five divisions, each with a separate area of responsibility. As part of these plans, any future nuclear expansion was ended. When Mike Harris' Conservatives regained power in 1995, Harris appointed Farlinger as CEO of Hydro and the plans were amended to sell off the various divisions once the split was complete.

By this time, Hydro had $34 billion in debt, almost half of that due to Darlington and a significant portion of the rest from construction and expansions on Pickering and Bruce. Additional charges were due to cost overruns on the boilers at these plants, which ran to $850 million. More was added due to the take-or-pay contracts with Rio Algom and Denison Mines for supply of uranium that were set at market rates prior to the collapse of worldwide uranium prices in the late 1980s. This led Hydro to break the contracts in 1991 at another $717 million charge.

After much debate, the decision was made to isolate the debts into a separate crown corporation, the Ontario Electricity Financial Corporation. Ontario Hydro officially ended operations on 31 March 1999. Their final financial statements listed long-term debts of $26.2 billion and assets totalling $39.6 billion, but the government concluded the fair value of the assets was far below the claimed price. Their valuations calculated a resulting $19.5 billion of stranded debt, which was then paid off as a separate Debt Retirement Charge on customer bills from 2003 until 31 March 2018.