from Lake Huron. There is (originally) one control room per 4 reactors. Bruce A Construction of Bruce A began in 1969, making it the successor to the Pickering A plant. Bruce A units were originally rated at 750 MWe net / 805 MWe gross, which was later increased to 769 MWe net / 825 MWe gross. the Bruce A units were capable of producing up to 779 MWe net according to IESO generator data. Each reactor requires 6240 fuel bundles that weigh 22.5 kg each, or about 140 tonnes of fuel. There are 480 fuel channels per reactor, containing 13 bundles each. There is storage capacity for about 23,000 bundles. Approximately 18 bundles are discharged per reactor per day. The original Bruce A steam generators utilized a separate large horizontal shared steam drum (with one steam drum common to four steam generators), a design dropped in most other plants at the time. Issues related to the AECL requested design of the tube supports caused repair and delay costs, which exceeded the net worth of the builder Babcock & Wilcox Canada. Until they were removed in 1998, Bruce A reactors used unique booster rods to control reactivity. Booster rods contained 93% uranium-235, and were inserted to overcome reactor poisoning. Bruce B and all other Ontario Hydro reactors instead use absorber rods called "adjusters" which are normally inserted and are removed to overcome xenon poisoning. Bruce A demonstrated an "excellent" early operating history. Together with Pickering A, the eight units achieved an overall average capability factor of 83% over the initial five-year period. However, by 2001, when Bruce Power took the lease, all Bruce A units were laid-up. In 1981, Unit 1 was ranked the top reactor in the world with a 97% availability factor. In December 1997, after about 20 years of operation, it was out of service. In 2005 (after 7 years of being idle) refurbishment started. In September 2012 (15 years out of service) it resumed operation. In 1982, Unit 2 was temporarily shut down due to a pressure-tube leak. In 1986, a fuel channel failed while the reactor was shut down; some of the fuel elements were swept into the moderator (calandria) and were difficult to remove. In 1986, maintenance workers accidentally left a protective lead blanket in the steam generator of Unit 2. By the time the mistake was discovered six years later, the blanket had melted,