Unit 1 at the Donald Cook nuclear power station in Michigan, USA, will not return to service until September 2009 at the earliest, and could remain off line until 2010, following damage to a turbine generator.
|The DC Cook plant (Image: AEP)
The unit has been off line since 20 September after the main turbine and generator were damaged by severe turbine vibrations caused by broken low-pressure turbine blades. Owner American Electric Power (AEP) had initially hoped to return the unit to service by the end of November, but now says that it faces two possibilities: a repair to the low-pressure turbine rotors which would enable a return to service, albeit at slightly reduced power, by September 2009, or the replacement of the rotors with new ones, which would take until some time in 2010.
According to AEP chairman, president and CEO Michael Morris, the company's current expectations are that the first option - a repair to the low-pressure turbine rotors and a September restart - should be achievable. Repair work has already begun, and involves straightening the rotor shafts and then modifying each rotor by removing one or two of the largest rows of blades until such time as new rotors are available. The removal of the blades would result in a power reduction of about 100-250 MWe from the unit's rated 1030 MWe capacity.
Should it not prove feasible to repair the rotors in this way, the restart will have to wait until new rotors, which are long lead-time items, can be manufactured.
The broken blades are in two of three new low-pressure turbines, manufactured by Siemens, which were installed in the unit in 2006. AEP says that the estimated $332 million cost of repairing and replacing the rotors will be recovered through insurance, vendor warranty or the regulatory process. The high-pressure turbine and main generator rotors, manufactured by General Electric, are undergoing repairs at a GE facility in Chicago, and are expected to be returned to the plant prior to the return of the repaired low-pressure turbine rotors.