The 672MW Mactaquac hydro generating station on the Saint John River near Fredericton, New Brunswick, has a special role in ensuring reliability of supply. There are 6 hydro-generators each of 100 MW, one of which is always kept on spinning reserve to preserve system stability in the event of loss of generation such as a trip of the Point Lepreau CANDU 6 nuclear plant to which it is connected by a 105km long 345KV line. The other hydro-generators can be made operational quickly. Sufficient headwater is kept in the dam to generate over 600MW for several hours. At most times of the year the headwater in the dam is limited so this 600MW is only available for long enough to enable the fossil fuel stations at Belledune and Coleson Cove to pick up the load. However during the spring run off, this 600MW can be maintained for a few weeks. This is when Lepreau regular annual shutdowns are planned resulting in high annual performance over the years.
The Mactaquac powerhouse has had a problem for many years due to concrete expansion; alkali-aggregate reaction (AAR). Starting in 1988, cuttings have been made in the concrete over the years to provide some relief; Reference (1) gives details and reports 5 cuttings to 1992. It mentions that this expansion could continue for at least 25 years. Additional cuttings have been made in recent years but are limited by the number of bays and two cuttings per bay.
Also but this concrete expansion has begun to affect the internal dimension around the water turbines, which will eventually make it impossible or uneconomic to refurbish all six water turbine generators.
There is a concept for rebuilding Mactaquac by constructing a new powerhouse from the existing powerhouse slipway, in a south direction to the existing public parking lot. Reference (2)
This powerhouse would be just down stream from the existing dam and road. The new generators could be run in parallel with the existing generators, so there would be no loss of output. The amount of water released through this combined dam would not exceed existing water height and flow limitations. The impact on salmon would not change because the salmon hatchery would continue to exist
(1) Canadian Consulting Engineer September/October 1993 pages 20 and 22, include excellent colored pictures of the dam and the intake structures slot cutting. Acres International - Niagara falls prepared the article.
(2) 2008 March; Talk at UNB Engineering Department on concepts for possible replacement of the Mactaquac Hydro Generating station.
Prepared by Neil Craik, 2010 March 30