ST. LOUIS -- The Callaway nuclear plant near Fulton will be closed for 10 weeks, as AmerenUE replaces four steam generators at an estimated cost of $200 million.
The project is the most expensive in the history of Callaway, which provides more than 10 percent of Missouri's electricity.
The steam generators are being replaced after 21 years because some of the alloy tubes inside are cracked and have been plugged, making them useless, the St. Louis Post-Dispatch reported in its Sunday editions. That has reduced the plant's 1,200-megawatt generating capacity and made inspections and repairs increasingly expensive, said Tim Herrmann, Ameren's manager of engineering services.
Water superheated by uranium fuel passes through the tubes and transfers heat to a second water system, which boils and creates steam to drive the plant's turbines and generate electricity.
The tubes are supposed to last the lifetime of the plant, but corroded and cracked tubes have been a consistent problem for nuclear plants for more than two decades. Steam generators at more than two dozen other plants already have been replaced, and three such projects, including Callaway, are scheduled for this fall.
More than a dozen utilities sued over defects in the tubes, and many reached out-of-court settlements. Ameren didn't sue, but reached a settlement for an undisclosed amount with Westinghouse Electric, the plant's manufacturer, Herrmann said.
Ameren has plugged about 3 percent of the 22,000 tubes at Callaway, a low percentage by industry standards and far less than what's allowed by the Nuclear Regulatory Commission, Herrmann said. But the utility chose to replace the steam generators to boost efficiency and avoid future problems.
"We were losing megawatts every time we had to plug one of those tubes," Herrmann said.
Ameren says the new steam generators at Callaway contain tubes made of an improved alloy that's more resistant to cracking and should last the rest of the plant's licensed 20-year life.
The company won't say if the expensive project means it will try to relicense the plant to operate beyond its Oct. 18, 2024, decommissioning date.
Nuclear operators can apply for relicensing 20 years before a plant's decommissioning, said Ken Clark, an NRC spokesman in Atlanta.
"We're seeing a majority of the plants in the U.S. go for relicensing, and there's no reason to believe that Callaway won't," said William Miller, a professor of nuclear science and engineering at the University of Missouri-Columbia, who also is on the plant's safety review board.
While the plant is off-line, Ameren also will replace four turbine rotors at a cost of $65 million because of cracks in the components, and refuel the plant. Later, Ameren is planning to retrofit the plant's control room with digital equipment.
The new steam generators and rotors will add about 60 megawatts of generating capacity, which should help recoup some of the project's cost, because Callaway will be able to generate more electricity with the same fuel.
The impact on customers has not been determined. Ameren will file a cost of service study with the Missouri Public Service Commission by the end of the year. Ameren's rates in Missouri are frozen until June 30, 2006.