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Saturday, April 6, 2002

NRC raps D-B for not finding reactor corrosion sooner

Feds say energy co. missed chances to find problems at power plant near Oak Harbor


Staff writer


OAK HARBOR -- Workers at Davis-Besse Nuclear Power Station should have seen the symptoms of corrosion problems at least four years ago, according to a preliminary federal report released Friday.

The energy company missed a number of opportunities to spot acid that ate through 6 inches of a steel cap on the plant's reactor, said Jack Grobe, who is one of several Nuclear Regulatory Commission members in town Friday for a public meeting with the operators of Davis-Besse, FirstEnergy Nuclear Operating Company.

The meeting became contentious at times, with protesters hooting and shouting out comments like "shut it down," and holding up signs during statements from NRC and FirstEnergy officials.

The NRC called the meeting to present its initial findings from a special inspection team sent to the plant at the beginning of March to review the corrosion problem.

FENOC Vice President Howard Bergendahl admitted to NRC officials and more than 300 visitors that FirstEnergy "could have and should found it in previous inspections."

"We believed it to be from other sources and we were mistaken," Bergendahl said. "The condition found was unexpected, but it is our responsibility to expect the unexpected, and we did not do so in this case."

NRC officials explained the corrosion problem in detail, as well as the missed opportunities that led to nearly 35 pounds of steel

being eaten away from the reactor head. Only a 3/8-inch thick stainless steel layer impervious to boric acid stopped the corrosion.

"Had it been pursued vigorously it could have been identified early so it wouldn't have become an issue," Grobe said. "This problem would have been prevented."

NRC officials cautioned, however, that there are three barriers to prevent a release of the low level radioactive coolant water, and none of the barriers were actually breached. Therefore, the corrosion problem posed no significant public health risk.

One of the tell tale signs, in hindsight, were radiation air filters in the containment area that were getting clogged with boric acid deposits back in 1999.

Boric acid is used in the cooling water to diffuse the nuclear reaction process, and it had been leaking out onto the reactor head.

While officials knew there was boric acid deposits caking the reactor head (to the point that crowbars and hot water were used to chip the deposits off the head), they thought the source was something else -- not a crack in one of the nozzles that protrude from the top of the reactor head.

The filters began to clog more frequently, NRC officials said, and Davis-Besse workers went from changing them monthly to every other day.

"This was a missed opportunity to identify leakage in the reactor head," said Mel Holmberg, a senior metallurgical engineer for the NRC.

Davis-Besse officials also dropped the ball when it came to a 1990 modification to improve access to the reactor head, NRC officials said.

Plant officials decided almost 12 years ago to modify the reactor head to allow greater accessibility to clean and inspect areas that are currently impossible to see and nearly impossible to maintain.

That modification, said NRC spokesman Jan Strasma, was pushed back during each routine outage since then and has never been implemented.

With that modification, Davis-Besse workers would have been able to spot the corrosion symptoms long before now, he said.

FirstEnergy officials are hoping to present a repair plan to the NRC for approval, and weld stainless steel to block off the corroded area.

The company also plans to replace the reactor head in 2004 with a new one currently being constructed in Japan.

Photo
Enlarge

Members of the Nuclear Regulatory Commission and FirstEnergy answered questions Friday from the public at a hearing in the Oak Harbor High School auditorium,

Boric acid leak linked to corroded reactor head

Experts believe boric acid in the nuclear reactor's cooling water ate away 6 inches of the reactor head, which is equivalent of 35 pounds of steel.

The reactor head is 6 inches deep, and only a 3/8 inch stainless steel lining that is impervious to boric acid stopped the corrosion from eating all the way through the cap.

Officials say boric acid apparently deposited on the reactor vessel through a crack that went all the way through a control rod nozzle.

There are 69 nozzles on the top of the reactor head, which rods pass through and control the reaction in the core.

The corrosion was found close to one of those nozzles as workers were repairing cracks in five of the nozzles, as mandated by the Nuclear Regulatory Commission.