The 16 story high vacuum building at Ontario's half billion dollar nuclear colossus at Pickering was encased with reinforced concrete in a non-slip slip-form operation in less than 8 days- 7 days, 10 and one-half hours, to be exact. This is believed to be the largest project of its kind ever attempted in North America. Engineers from the Hydro Electric Power Commission of Ontario spent a year in working out plans and three and a half additional months setting down the multitude of details. They pointed out that once started the operation could not be stopped, as their plans called for a "seamless" outer coating around the vacuum building. Any stoppage of work would have sidetracked this accomplishment. The vacuum building, a key part of Pickering's containment system, is supported by about a thousand 50 foot steel piles driven to bedrock. The walls are 3 feet thick and the roof is a 2 foot thick reinforced slab. The vacuum building and pressure relief system are collectively designed to contain all the energy that could be released following any conceivable accident to the reactor heat transport system and to provide complete protection for the public. Sixty-four hydraulic jacks were used to raise the forms. Each had a capacity of 22 tons and the system was capable of cycling in 3 minutes. Concrete was placed in amount varying from 30 to 70 yards an hour, depending on the status of the project. A dispatcher controlled the movement of the concrete trucks from a nearby plant. Arrangements had been made for a capacity of 120 yards an hour if necessary, with a standby plant capable of producing 40 yards an hour. The concrete, after being placed, was rubbed down by cement masons on the hanging scaffold. Curing was achieved by spraying the concrete immediately after it had been rubbed down with a special curing compound.