severely damaging the boiler. In October 1995, after about 18 years of operation, unit 2 was taken out of service. In 2005 (after 9 years of being idle) refurbishment started. In October 2012, it resumed operation. In 1982, Unit 3 set a then world record of 494 days of continuous operation and Bruce A was the most reliable multi-unit station in the world. From April 1998 onward, Bruce A3 remained idle for 6 years, returning to service in January 2004 (at which time the unit was 32 years old). Planned refurbishment of the third unit is to begin in 2023 (when the unit will be 51 years old). In 1990, a software error in unit 4 caused a fueling-machine error, damaging a fuel channel. In 1993, reactor power was reduced to 60% until various loss-of-coolant accident (LOCA) scenarios could be addressed. Subsequently, Bruce A units returned to 89% of rated power. In March 1998, after about 19 years of operation, unit 4 was taken out of service. It returned to service in October 2003, after 6 years of being idle (at which time the unit was 31 years old). Planned refurbishment of unit 4 to begin in 2025 (when the unit will be 53 years old). Bruce B Bruce B units, located to the south of Bruce A, are of a slightly larger capacity: 817 MW net, 840 MW gross. which is attributed to an improved steam generator design, where the steam drum is integral to each steam generator in a "light bulb" arrangement, eliminating the horizontal cross-drum. In 1990, a nine-week "impairment" of Bruce B was created when a technician incorrectly set the calibration on radioactivity monitors. In 2007, Bruce B 7 was the top performing nuclear reactor in Ontario with 97.2% performance. and in 2009, Bruce B 5 was first with 95.4% performance. Bruce B 5 Construction began 1 June 1978. On 15 November 1984 it reached first criticality. Commercial operation began on 1 March 1985. Originally scheduled to be shut down in 2016 (unit would have been 31 years old). Planned refurbishment to begin in 2026 (unit will be 41 years old). Bruce B 6 Construction began 1 January 1978. On 29 May 1984 it reached first criticality. Commercial operation began on 14 September 1984. Originally scheduled to be shut down in 2018 (unit would have been 34 years old). Planned refurbishment to begin in 2020 (unit