One up, one down at Ontario Bruce nuclear plant

NEW YORK, Nov 11 (Reuters) - Bruce Power LP's 750-megawatt Unit 4 at the Bruce nuclear power station in Ontario returned to service on Nov. 10, while the 822-MW Unit 6 shut for short maintenance, the company said in releases.

Unit 4 shut by Sept. 5 for maintenance and the planned inspection of the Bruce A vacuum building.

The vacuum building is designed to prevent the release of radioactive material to the environment in the unlikely event of an accident.

It is a large cylindrical structure connected to the generating station by a pressure relief duct and kept at negative atmospheric pressure so any potential release of radioactive steam can be sucked into the structure.

The Canadian Nuclear Safety Commission requires inspections of the structure every 12 years.

Unit 4 last shut for maintenance from about March 26 to April 27, 2008. It is on an 18-month maintenance cycle.

All of the other units remained in service.

The 6,261-MW Bruce station is located in Tiverton on the eastern shore of Lake Huron about 155 miles (250 km) northwest of Toronto. There are four 750-MW units, 1 to 4, at the A station, which entered service in 1977 to 1979, and three 822-MW units, 5 to 7, and one 795-MW unit, 8, at the B station, which entered service in 1984 to 1987.

The company expected to increase Unit 8's output to about 822 MW by modifying the fuel-loading system by early 2010.