Special repairs to the Bersimis-1 generating tunnel walls to increase power production: a case study

The intake concrete tunnel at Bersimis-1 generating station is coated with a black sticky substance (slime) approximately 5 mm in thickness. Since the tunnel is 12 km long and has an average internal diameter of 9.45 m, the d eposit represents a considerable obstacle to the production of electric pow er. The resulting loss of power generated is estimated to be around 39 MW p er year, valued at 71 million dollars. Inspections in 1979, 1981, and 1983 showed that simply cleaning the surfaces would reduce the power losses but the slime built up again after a few years. A thin, smooth protective coati ng, containing anti-slime agents, compatible with the existing concrete cou ld protect the surfaces against erosion and limit the slime deposit and its harmful effect on power production. The 1993 inspection provided an opport unity both to analyze the concrete, the slime itself, and the water and to experiment with the various methods of cleaning the surface and applying th e different coating products. In 1994, 11 other products were selected for the specified characteristics and applied on concrete pipes and installed a t two different locations: one consisted of submerged concrete specimens in the Bersimis river and in the second test setup, the products were install ed by creating an artificial environment similar to the tunnel conditions u sing the tunnel water. The results showed that some products do not resist these conditions. Abrasion resistance tests in the laboratory confirmed the se observations. One of the eleven products, a polymer-modified cement-base d mortar, passed the submersion test and was applied to a small surface are a (125 m(2)) of the tunnel during a generating station shutdown in 1995. Th e thickness of the mortar required to cover the walls of the tunnel was bet ween 2 and 3 mm. The total cost of repairing with the mortar was estimated to be between 10 and 11 million dollars. The size of the tunnel, its restri cted accessibility, cleaning, ecological disposal of the slime, and the lar ge quantities of material to be applied to cover the entire tunnel added to the complexity of the project.