Bruce Power says the temporary shutdown of all four units at Bruce B has wrapped up.
The Bruce B Vacuum Building inspection and maintenance program is conducted about every 10 years.
Unit 8 was returned to the grid Sunday evening, and Unit 5 was back on line shortly after that.
Unit 7 returned to service yesterday.
The planned maintenance and inspection of Unit 6 that began in April is expected to wrap up in the third quarter of 2015.
The 30 million dollar investment created 300 temporary jobs at the site.
The concrete vacuum building has walls about a metre thick, to contain radioactivity, in the unlikely event of a large loss of reactor coolant. During normal operation, the air inside the vacuum building is maintained at one-tenth atmospheric pressure by vacuum pumps in the upper and lower chambers. The vacuum building is separated from the station containment structure by an array of 18 large pressure relief valves which are connected to massive tubes at the base of the Vacuum Building. In the event of a loss of coolant, any radioactive steam would be travel into the vacuum building and be doused with water and contained.
“This outstanding result can be attributed to an unwavering commitment to safety, a strong operational focus, hard work, effective teamwork and a high level of engagement,” said Brian O’Grady, Senior Vice President at Bruce B. “I want to thank our staff for all their hard work and dedication. This is something we can all be very proud of.”