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Regulators say Ohio nuclear plant only one to have boric acid buildup

The Associated Press
4/9/02 8:57 PM

WASHINGTON (AP) -- Preliminary findings of an industrywide review have turned up nothing similar to the circumstances that led to boric acid nearly eating through the 6-inch tick metal reactor cap at a northwest Ohio power plant, federal regulators said Tuesday.

Officials at the Nuclear Regulatory Commission told an advisory panel that they still need to closely review many of the responses from the industry, but that none reported major concentrations of boric acid atop their reactor vessels.

"We haven't seen anything similar so far," said Jack Strosnider, director of the NRC's engineering division. But he said the agency is "casting a wide net" to ensure that reactor operators take steps to inspect the reactor vessels for boric acid accumulations.

The industry and federal regulators were caught by surprise when it was discovered in March that longtime leaks in reactor nozzles had resulted in a large accumulation of boric acid atop the reactor vessel at the Davis Besse plant. It burned a 7-inch wide hole almost through the 6-inch thick steel vessel containing the reactor fuel. The plant is along Lake Erie and about 25 miles east of Toledo.

Only a three-eights of an inch inner lining, made of noncorrosive stainless steel, prevented the hole from penetrating into the reactor core and causing a loss of vital cooling water and possibly further problems.

After the incident, the NRC directed operators of all 68 other similarly designed pressurized reactors across the country to inspect rector vessels or give other assurances that they did not have a dangerous buildup of boric acid, which is contained in reactor cooling water.

Industry representatives told the advisory panel that operators of 27 reactors have reported some boric acid leakage. In 22 of the cases, there was no accumulation of acid found on the reactor vessel. But in five other cases, inspections were limited or could not be performed and more information is being prepared, officials said.

Larry Matthews, an official of Southern Nuclear and chairman of an industry task force looking at the pressure nozzle leaking problem, said no one has found any indication of rector vessel corrosion such as occurred at the Ohio plant.

Operators of 41 other reactors reported no boric acid deposits after conducting new inspections or reviewing recent inspection records, he said.

Officials of FirstEnergy Nuclear Operating Co., which runs the Davis Besse plant, said they have concluded that cracks that caused major leaks of water in one of the reactor nozzles were the root cause of the accumulation of boric acid that ate into the top of the 6-inch thick steel vessel containing the reactor fuel.

Steve Loehlein, leader of the company's team investigating the incident, said the nozzle probably had been leaking since 1994, at times leaking as much as 12 gallons of water per hour. Boric acid had accumulated at the top of the reactor vessel where the leaking nozzle was situated and the corrosion had probably been under way for at least four years, he said.

Leaks are not uncommon at power plants. But the water normally turns immediately into steam as it leaves the highly pressurized reactor vessel turning the boric acid into a harmless powder.

In the case of Davis Besse, investigators have speculated that for some reason moisture remained -- perhaps because of the long accumulation of residue -- creating boric acid, which is highly corrosive to the carbon steel. The top of the reactor vessel is difficult to access and observe. Insulation is located just inches above the vessel.

But NRC inspectors told the advisory panel that there were several "missed opportunities" for the operators of the Davis Besse plant to head off serious problems. There were several indications that serious corrosion was occurring atop the rector vessel, but those indictors were not pursued, the panel was told.

The early warnings were outlined earlier this week by the NRC at a public meeting in Ohio.


On the Net:

U.S. Nuclear Regulatory Commission: http://www.nrc.gov

Copyright 2002 Associated Press. All rights reserved.
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