Nuclear Plant Finds Blister, Corrosion
A Pennsylvania nuclear plant is again reporting a coating defect and corrosion in one of its units, near the site of decayed wood left in the structure.
The latest defect, a coating blister, was discovered Friday (Oct. 4) during a routine inspection at Beaver Valley Power Station Unit 1 in Shippingport, PA, about 35 miles northwest of Pittsburgh on the Ohio River.
The unit was shut down Sept. 30 for refueling, maintenance and a turbine upgrade "designed to improve efficiency and reliability," owner FirstEnergy Nuclear Operating Company announced.
Old Wood, New Suspect
A 40-year-old piece of wood likely caused the hole, officials said, making this the third time in seven years that old wood and corrosion were discovered together at the plant.
The paint blister was discovered about seven inches off the ground.
Initially, the company was unsure of the cause, but it later reported that a piece of wood—left over from the building's construction in the mid-1970s—was likely still embedded in the concrete wall, causing the steel liner to corrode, media reports stated.
"A piece of fibrous material, likely wood, decayed and created moisture," said Jennifer Young, spokeswoman for FirstEnergy, according to the Pittsburgh Post-Gazette.
An area about 0.4 inches by 0.28 inches was discovered that "penetrated through the containment steel liner plate," Nuclear Regulatory Commission officials said.
The containment building is made of a 4.5-foot-thick concrete wall and a 3/8-inch-thick steel liner.
In an Event Notification from the NRC dated Oct. 5 and obtained Wednesday (Oct. 9) by PaintSquare News, the agency did not identify a cause of the defect, saying that the "cause of this discrepancy is currently being evaluated."
FirstEnergy is performing ultrasonic testing of the coatings flaw and surrounding areas, Neil Sheehan, NRC Public Affairs Officer, said via email Wednesday.
"Our Resident Inspectors assigned to Beaver Valley on a full-time basis will continue to follow up on what FirstEnergy learns from the testing, any repairs and its root-cause evaluation," Sheehan wrote.
Young told the Post-Gazette that the degradation posed no harm to public health and safety, and that the inspection process "did exactly what it was supposed to"—detect the defect before it became a bigger problem.
A request for more information from FirstEnergy was not immediately returned on Wednesday.
Foreign Objects in Containment
In 2009, during a refueling outage at Unit 1, an area of intact blistered paint, about three inches in diameter, was found in the steel liner. Underneath the blister, inspectors discovered "a protruding rust product" that penetrated the entire plate thickness of the liner.
|NRC / FirstEnergy|
This paint blister was discovered at Unit 1 in 2009. Decomposed wood was found underneath, and corrosion had penetrated the entire steel liner.
The culprit was a partially decomposed piece of wood embedded in the concrete, which was left behind "as a result of inadequate housekeeping and quality assurance practices" during construction in the early 1970s, the NRC reported.
In 2006, during temporary construction of an opening in Unit 1's containment structure, three areas of corrosion were discovered, according to the NRC. The probable cause was reported as exposure to oxygen and water during construction. The NRC also said that several pieces of wood had been found during inspection of the concrete debris pile, but that "no clear evidence" confirmed that the wood had caused the damage.
The holes are typically repaired by cleaning the area, grouting the concrete, welding a new steel patch to the liner, and testing its integrity, officials said.
|NRC / FirstEnergy|
Three areas of corrosion were found during a 2006 inspection of Unit 1. Several pieces of wood were discovered in the concrete debris, but the NRC could not confirm that had caused the damage.
In the U.S., 66 power plants have containment buildings constructed with an inner steel liner plate and a thick concrete shell, and foreign objects have caused corrosion issues in several nuclear power plants over the years.
While many of the instances involved old pieces of wood, the NRC has also reported a work glove and a wire brush with a wooden handle embedded in the concrete walls of nuclear plants.
At Beaver Valley, 60 of the 157 fuel assemblies will be replaced while Unit 1 is offlline, and preventive maintenance will be performed on major components, including the plant's three steam generators, various pumps, valves and the cooling tower.
Unit 1's two low-pressure steam turbine rotors will be replaced with ones that feature an enhanced blade design that is "expected improve plant reliability, efficiency and life expectation," according to FirstEnergy.
According to FirstEnergy, "The 911-megawatt Beaver Valley Unit 1 operated safely and reliably for 507 consecutive days since the completion of its last refueling outage in May 2012."
The company did not say when the plant would return to service.
Originally licensed to operate for 40 years, the plant was issued a renewed license on Nov. 5, 2009, extending the lives of the units until 2036 and 2047.
In addition to the Beaver Valley Nuclear Power Station, Akron, OH-based FirstEnergy operates the Davis-Besse Nuclear Power Station in Oak Harbor, OH, and the Perry Nuclear Power Plant in Perry, OH.