Monday, January 14, 2008
Small leakage of radioactive water reported at Davis-Besse nuclear plant
January 8, 2008
OAK HARBOR, Ohio — Radioactive coolant water seeped from a pipe in the Davis-Besse nuclear power plant's containment area Friday morning as an old weld was being reinforced with a metal overlay, FirstEnergy Corp. and federal officials said yesterday.
The leakage was too small to be measured, officials said.
The utility and the Nuclear Regulatory Commission said the leak did not harm workers, who were wearing protective clothing. The nuclear plant has been idle since late December for refueling.
The pipe in question is part of the reactor coolant system's decay heat suction line.
The same tube had moisture on it yesterday afternoon. But leakage was so inconsequential it was "not dripping," Marla Lark-Landis, a FirstEnergy spokesman, said.
FirstEnergy is in the process of reinforcing 16 of the plant's aging welds.
Attempts to reinforce the leaking one were halted until FirstEnergy determines the crack's type, location, and size. An ultrasonic examination that is expected to be done today will help the utility determine its course of action for the fix, she said.
Todd Schneider, another utility spokesman, said the repair is not expected to delay the plant's restart.
Nuclear plants are refueled once every 18 months to two years, with outages typically lasting 30 to 45 days.
Viktoria Mitlyng, NRC spokesman, said the crack appears to have occurred as FirstEnergy was complying with an agency directive to reinforce welds at which two different types of metal meet.
"They were in the process of applying the fix when the leakage occurred," she said.
Scott Burnell, another NRC spokesman, said the nuclear industry and the regulator have agreed that welds with differing types of metal need to be reinforced at plants with pressurized water reactors.
Such welds can eventually give out because of their chemical makeup, plus the stress placed on them from that type of reactor's enormous operating pressure and temperature, the NRC said.
Davis-Besse is one of the few nuclear plants that operates in excess of 600 degrees.
"The basic issue has been understood for several years," Mr. Burnell said. "When you have two different metals welded together in a [pressurized water] reactor environment, you can see cracking in that area."
NRC records show the first cracked weld involving two or more types of metal was documented in 1993.
In 2000, the regulatory commission and the industry agreed to give the issue more attention after more cracks were discovered.
The latest round of inspections were formalized last March, via an NRC document known as a confirmatory action letter.
Forty plants, including Davis-Besse, were put on notice to expedite their inspection plans.
The NRC cited its concern over the size and nature of cracks in pressurizer welds found at the Wolf Creek reactor near Burlington, Kan., in October, 2006.
Five circular cracks — the most dangerous — were found in three Wolf Creek welds that had mixed metals.
An NRC fact sheet said that was the first time multiple cracks of that type had been identified. The Wolf Creek incident raised questions about "the degree of safety margin present in past structural integrity evaluations," the agency said.
Davis-Besse is along Ottawa County's Lake Erie shoreline, about 30 miles east of Toledo.
It is one of 70 nuclear plants with pressurized water reactors. The other 34, including DTE Energy's Fermi 2 nuclear plant north of Monroe, have boiling water reactors that operate at lower pressure and temperature.
Changes are being contemplated for all plants in the American Society of Mechanical Engineers codes, the NRC said.
The Union of Concerned Scientists, a watchdog group based in Cambridge, Mass., said in a briefing issued by its Washington office yesterday that the repair at Davis-Besse could be "relatively simple" if the lone discovered crack turns out to be the plant's only one.
"If not, the repairs and risk implications grow larger," according to the paper, written by David Lochbaum, a former nuclear safety engineer and the group's nuclear safety project director.