The Ontario Power Generation (OPG) Pickering B Facility consists of four 540 MW nuclear generating units. Each unit is furnished with a once-through Condenser Cooling Water (CCW) System that uses Lake Ontario water. Zebra mussels (Dreissena polymorpha) are infesting the condenser cooling water intakes at Pickering. The mature mussels and their shells become entrained in the CCW, are deposited in the condenser inlet water boxes, and become lodged in the condenser tube sheets and within the tubes. As a result, the flow through the condenser is reduced, and the existing Condenser Tube Cleaning System (CTCS) performance is degraded. This reduces the Turbine-Generator generating capability that results in a loss of electric generation revenues for OPG, and increased maintenance costs to manually remove the zebra mussels from the condenser. OPG decided to install Debris Filters in the six 72-inch diameter inlets of each of the four Pickering B units to automatically remove the zebra mussels before they enter the condensers and discharge them back into the lake. The Debris Filters for Unit 8 were installed during a scheduled outage in the winter of 2001/2002. The Unit 5 installation was completed at the end of 2002 and the Unit 6 & 7 installations are scheduled for 2003. The installed equipment is performing as expected. The zebra mussels are intercepted by the Debris Filter, and are automatically discharged into the condenser bypass and returned to the lake. The CTCS system can again perform its intended function to prevent bio-fouling buildup inside the condenser tubes. As a result, generation capacity increased and maintenance expenditures decreased with a net result of increased revenues for OPG.

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