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A reactor at the nation's largest nuclear power plant was shut down because of a growing vibration in a coolant pipe.
Arizona Public Service Co. had been operating the reactor, one of three at the Palo Verde Nuclear Generating Station, at about one-third of capacity because of vibration, but operators decided to shut it down Tuesday after the vibration rose above acceptable levels.
The unit could be restarted within two days, said a spokesman for Arizona Public, Jim McDonald.
Potential fixes could include adding shock absorbers, installing weights or heating the line. McDonald said the coolant line is used only the reactor is being shut down. "It's used at low temperatures and low power when you're bringing the plant off-line," he said.
The utility said the installation of the unit's new 800-ton steam generators and low-pressure turbines could have contributed to the increased vibration.
Problems over the last two years at Palo Verde, about 50 miles west of downtown Phoenix, have caused more than a dozen shutdowns.
Arizona Public owns 29.5 percent of the plant and operates it for a consortium of utilities. It supplies electricity to about 4 million customers in Arizona, New Mexico, Texas and California.