Ah…spring outage time. At the Davis Besse (DB) plant in Oak Harbor, Ohio, the words “spring cleaning” took on new meaning. Secondary-side chemical cleaning of the plant’s two once-through steam generators (OTSGs) was in full swing, and life was good.

“It was the smoothest SG cleaning operation I’ve ever been involved with,” said Ron King, Supervisor, Application Engineering and Chemical Cleaning Task Leader for Framatome Technologies. “Everyone cooperated, and the plant team worked well with our team members to get the job completed in record time.”

“In fact, the job was completed 42 hours ahead of schedule,” King said.

“It was a good job,” said Richard Chesko, Sr. Engineer - Projects at DB. “The Framatome team, and our personnel all deserve an ‘Atta Boy,’” he declared. “Due to previous replacement of our main feedwater nozzles and this being the first time our generators were cleaned, we all expected improved operating levels. When the unit started back up, we were extraordinarily pleased to find that operating levels were even better than original startup levels.”

The SGs at Davis Besse have been in operation since 1977 without a cleaning or replacement. Once-through steam generators are unusual in the industry. These workhorses of nuclear power are approximately 68 feet high and 13 feet in diameter, so cleaning one requires miles of hoses, tons of chemicals and numerous holding tanks – so many, in fact, it is termed a tank farm. All this equipment is moved to the site for the operation, and then dismantled and sent to the next job.

During the Davis Besse outage, Framatome Technologies used the Electric Power Research Institute/SG Owners Group (EPRI/SGOG) low-temperature method to remove magnetite deposit buildup in the OTSGs that accumulated during years of service. The deposits had built up in the broached openings of the tube-support plates, and in turn were causing increased pressure drop on the secondary side. Had the deposit buildup not been removed, power output would eventually have had to be reduced, which is an extremely undesirable condition in today’s competitive marketplace.

More than 5,000 pounds of deposits were removed during the cleaning. SG 1 was cleaned in approximately 100 hours, removing 2,600 pounds of deposits. SG 2 took approximately 120 hours and 2,500 pounds of deposit were removed. Following the chemical cleaning, an additional 900 pounds were removed by sludge lancing. After the cleaning operations were complete, eddy-current testing and visual inspections clearly demonstrated that the SGs were essentially 100 percent free of debris or deposits of any kind.

Other OTSGs have had similar results – the generators FTI cleaned at two other sites produced between 6000 and 9000 pounds of deposits. The average OTSG deposit removal is 7,000 pounds. The Westinghouse recirculating steam generator averages 14,000 pounds. Some chemical cleanings that FTI has performed have removed over 35,000 pounds of deposits.

Radiation dose levels for the Davis Besse chemical cleaning were the lowest ever for FTI for this type of chemical cleaning, due in part to the timesaving on various steps of the operation.

Waste Processing
Waste processing at Davis Besse also took five fewer days than anticipated. FTI performed its standard waste-reduction of the liquid waste generated by the cleaning process. More than 83,000 gallons of waste were processed through a four-pass, forced-circulation evaporator to produce approximately 71,000 gallons of distillate solution that was released back to the plant. An additional 12,000 gallons of concentrated solution was shipped off-site to a low-level radioactive-waste treatment facility for further treatment and subsequent shipment for disposal.

“All in all, we were very pleased with the cooperation between the two teams, the smoothness of operations, and the final results,” said King.

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