The Tennessee Valley Authority expects to spend $55 million to fix a design flaw at its Raccoon Mountain Pumped Storage Facility and may have to delay scheduled closings of some of its oldest coal-fired units while such repairs continue until 2014.
But TVA's chief generation officer says the costs could have been far greater if cracked rotors in the hydroelectric station had not been identified and an accident occurred.
"This is a situation that could have been devastating," TVA Executive Vice President Kim Greene told the TVA board last week. "We've taken proactive steps to inspect the units and take them down ... as we have discovered significant cracking in the rotors."
A similar pumped storage plant in Vorarlberg, Austria, caught fire in July 2009, causing $40 million in damage to the unit after a rotor pole broke from the rotor rim. The German firm that designed both the Austrian and Raccoon Mountain facilities, Voith Hydro, alerted TVA in 2010 to the potential for a similar failure at Raccoon Mountain.
TVA disassembled the rotor of Unit 3 at Raccoon Mountain in November 2010 and found no problems with the Unit 3 rotors.
But an inspection in February during the outage of Unit 2 found widespread evidence of rotor cracks. TVA immediately suspended power production from the other units, and inspectors soon found cracks in those units, as well. TVA is having to repalce most of the 7,000-pound rotor poles and rotor rims.
"Our engineers felt that this was very serious, and we wanted to inspect the other units immediately," Greene said. "While certainly living without the Raccoon Mountain units has been difficult from an operational perspective, the potential damage that could have been done to our assets and, most importantly the damage that could have been done to our people, certainly warranted us taking this conservative approach."
The generators and pumps for TVA's pumped storage facility are located within Raccoon Mountain, and a fire like what occurred in Austria could have endangered the lives of plant workers and destroyed parts of the plant.
TVA engineers estimate that replacing each of the four units at Raccoon Mountain, if damaged or destroyed by fire, could range from $50 million to $150 million.
"Our total costs for the repair and replacement of all four units is estimated now to be about $55 million," Greene said.
In its annual report released Friday, TVA disclosed that it has delayed the shutdown of four aging units at Johnsonville coal plant in Tennessee and Unit 5 at its Colbert coal plant in Alabama.
"Due to unanticipated operating challenges primarily at Raccoon Mountain Pumped-Storage Plant, TVA is re-evaluating the previously announced idling dates of these units," TVA said in a regulatory filing Friday. "Depending on capacity needs, TVA may return other idled units into service or extend unit operation beyond previously planned idle dates."
TVA said it still expects to comply with the clean air agreements under which TVA pledged to shut down its oldest and dirtiest coal units.
TVA completed the $310 million pumped storage plant on Raccoon Mountain in 1978.
A lake was erected atop the mountain, and water is pumped up from the nearby Tennessee River to be stored in the mountaintop reservoir like a giant battery that can generate power from the lake during peak periods of power demand.
Collectively, the four units at Raccoon Mountain are capable of generating 1,616 megawatts of electricity -- or more than any of TVA's nuclear reactors.
"These units cycle," TVA President Tom Kilgore explained. "Those generators become motors, and then they turn back into generators so the stress is much greater (than in a conventional hydroelectric unit). That's probably where the original damage came from."
One of the four units at Raccoon Mountain returned to limited service with a partially restacked rotor last month. TVA said in its annual report that all of the units likely will return to full service "in the 2013 to 2014 timeframe."
Contact Dave Flessner at email@example.com or at 757-6340.