Once again poor OPG gets roasted for the wrong things. Although the secretive part is right, a tiny hole in the pressure relief duct is nothing, and could be postponed until the next planned outage. If people were that worried, they could just slap a bandaid on the outside.
The whole vacuum building thing is just a superfluous safety feature, added to deal with a slight Candu problem: too much water! It seemed to be a Biblical thing that they had to deal with a giant Transformer Autobot ripping a major steam line in half. In that case, the vacuum building (a little bit of Outer Space), would open its valves and start its Mummy Returns act. The pressure relief duct connects this Giant Sucking Sound to the steam break. When this system is activated, any little holes will quickly be plugged up by the sucked-up seagulls! Needless to say, there is a snowball's chance in Heck, that this ridiculous system will ever be needed (or work!), and the newer reactors don't have them.
Working at OPG (especially Pickering!) is psychological torture, so I feel for the little guy that leaked this. They should open up the SCR system, so people can see how darn-tootin' long it is! This little thing has been blown out of proportion, but there are far worse things on that SCR list, especially in light of the recent Japan nuclear brouhaha.