Operators had shut the plant down to investigate why one of the plant's four turbine control valves would not open fully. These valves, located in the non-nuclear part of the plant, regulate the flow of steam to the turbines that drive the generator to produce electricity.
AmerenUE officials say they discovered the problem was actually due to an internal fault in the plant's high pressure turbine, and as a result, the turbine had to be disassembled for inspection and repair. They emphasize that this was a mechanical problem that could occur in any type of steam plant, and did not present any danger to the public.
AmerenUE officials add that the turbine was new, having been installed in the fall of 2005, and the repairs were made by the turbine manufacturer under warranty.
While the plant was out of service, workers also performed nearly 300 other maintenance activities to ensure top performance during the upcoming summer season when electricity usage is the highest of the year.
In 2005, the Callaway Plant was the third largest power producer on the Ameren system\-accounting for 10.3 percent of total generation. Its net generation of 1,190 megawatts is enough to supply more than 656,000 average homes.
AmerenUE is a subsidiary of St. Louis-based Ameren Corporation. The Ameren companies serve 2.4 million electric customers and nearly one million natural gas customers in a 64,000-square-mile area of Missouri and Illinois.
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