will be 36 years old). Bruce B 7 Construction began 1 May 1979. On 7 January 1986 it reached first criticality. Commercial operation began on 10 April 1986. Originally scheduled to be shut down in 2015 (unit would have been 29 years old). Planned refurbishment to begin in 2028 (unit will be 42 years old). Bruce B 8 Construction began 1 August 1979. On 15 February 1987 it reached first criticality. Commercial operation began on 22 May 1987. Originally scheduled to be shut down in 2019 (unit would have been 32 years old). Planned refurbishment to begin in 2030 (unit will be 43 years old). Electrical output The graph represents the annual electricity generation at the site (A and B combined) in TWh. In 2013, it was about 30% of Ontario's production. As of the end of 2021, the total lifetime output of the facility was 1,522 TWh. Notable Achievements In 2009 total site output hit 1,002 TWh, making it the first nuclear power plant in the world to produce 1 PWh (1,000 TWh). Gravelines in France achieved the same in 2010. As of the end of 2020, the 8 Bruce units had produced a combined total of 1,479.59 TWh. After Units 1–2 completed refurbishment activities and were brought back online in 2012, Bruce became the largest operating nuclear generation facility in the world by both the number of currently operational reactors and total net output capacity, having a total of 8 operational CANDU nuclear reactors with a combined output of 6,384 MWe net (7,276 MWe gross) when all units are online. (The Kashiwazaki-Kariwa Nuclear Power Plant in Japan had a larger total output capacity, but it has been out of service since 2011.) Transmission Lines As of 2008, the Bruce station had three double-circuit 500 kV transmission lines to feed the major load centres in southern Ontario, in addition to three double-circuit 230 kV lines serving the local area. These circuits are connected via two high voltage switchyards owned and operated by Hydro One. In 2006, OPA had proposed increasing transmission line capacity, at a cost of between $200–600 million, described as "the largest electricity transmission investment in Ontario in the last 20 years." The line was completed in June 2012, several months ahead of schedule, with over 700 towers built for the 180 kilometre line to Milton. The project ranked 45th in Renew Canada's annual list. Comparison with