Darlington Nuclear Generating Station is a Canadian nuclear power station located on the north shore of Lake Ontario in Clarington, Ontario. It is a large nuclear facility comprising four CANDU nuclear reactors with a total output of 3,512 MWe (capacity net) when all units are online. It is Canada's second-largest nuclear power plant and provides about 20 percent of Ontario's electricity needs, enough to serve a city of two million people. It is named for the Township of Darlington (now part of Clarington), the name of the municipality in which it is located at the time of its planning. Construction and operation The facility was constructed in stages between 1981 and 1993 by the provincial Crown corporation, Ontario Hydro. Unit 2 was brought online in 1990, Unit 1 in 1992, and Units 3 and 4 in 1993. In April 1999 Ontario Hydro was split into 5 component Crown corporations with Ontario Power Generation (OPG) taking over all electrical generating stations. The Darlington reactors have been among the best performing in OPG's CANDU fleet, including a top year in 2008 in which the plant achieved a combined 94.5% capacity factor. In June 2016, the World Association of Nuclear Operators (WANO) named Darlington one of the safest and top performing nuclear stations in the world - for the third time in a row. After public hearings, the Canadian Nuclear Safety Commission announced in December 2015 the renewal of Darlington’s power reactor operating licence, for a 10 year period from Jan. 1, 2016 until Nov. 30, 2025, to allow for the refurbishment of the Darlington station, which began in October 2016. In March 2017, Ontario Power Generation (OPG) and its venture arm, Canadian Nuclear Partners, announced plans to produce Plutonium-238 as a second source for NASA. Rods containing Np-237 will be fabricated by Pacific Northwest National Laboratory (PNNL) in Washington State and shipped to OPG's Darlington Nuclear Generating Station where they will be irradiated with neutrons inside the reactor's core to produce Pu-238. Electrical Output The graph represents the annual electricity generation at the site in TWh. As of the end of 2021, the total lifetime output of the facility was 929.24 TWh. Cost overruns The Darlington station incurred massive cost overruns during its construction. The initial cost estimate for the station was $3.9 billion CAD in the late 1970s, which increased to $7.4 billion in 1981 when construction was started. A year-long