A weakened weld on the reactor vessel head of FirstEnergy's Beaver Valley Unit 2, in Shippingport, Beaver County, must be patched before the reactor is restarted.
The problem was discovered last week during a planned ultrasonic examination of the 66 welds around where tubes penetrate the reactor vessel head, said Jennifer Young, a FirstEnergy spokeswoman.
"We'll repair it by doing an overlay with a stronger alloy metal," said Ms. Young, who described the weld weakness as microscopic. "There was no indication of any leakage of any sort of material. The inspections did just what they are designed to do," find weaknesses before they can become a problem.
The nuclear reactor, one of two at the Shippingport power plant, was shut down for routine refueling and maintenance at the time the reactor cap was examined, and Ms. Young said Monday the repair work will not delay its restart.
A similar weld weakness was discovered during Unit 2's last refueling outage in 2012, and the latest flaw is the eighth found on the Unit 2 reactor's original vessel head, she said.
Neil Sheehan, a Nuclear Regulatory Commission spokesman, said the weld weakness is best described as "a flaw that, left untreated, could develop into a crack." He said "multiple pressurized-water reactors have replaced their heads because of this issue."
An NRC "specialist inspector" is at Beaver Valley and will review the company's repair plans. He also will check on other results from those inspections, Mr. Sheehan said in an email response to questions.
FirstEnergy plans to replace the steam generator and Unit 2 reactor vessel head in 2017, and the latest problem will not alter that schedule, Ms. Young said. The reactor started operating in 1987.
Similar generator and reactor head replacement was performed on the Beaver Valley Unit 1 reactor in 2006. Unit 1 went online in 1976.
The original reactor head metal was made from Inconel Alloy 600, an oxidation- and corrosion-resistant metal alloy that is 75 percent nickel, 16 percent chromium and 9 percent iron. But most replacement heads are made from Alloy 690, which is 60 percent nickel, 30 percent chromium and 9 percent iron, and offers "even better degradation resistance in reactor water environments" where the temperature is about 550 degrees Fahrenheit, Mr. Sheehan said.
Both Beaver Valley units have been granted 20-year license extensions. The extension for Unit 1 runs until 2036, for Unit 2 until 2047.
Together the pressurized water reactors produce more than 1,800 megawatts of power.
Don Hopey: firstname.lastname@example.org or 412-263-1983.