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U.S. Orders Checks for Corrosion at Nuclear Re



U.S. Orders Checks for Corrosion at Nuclear Reactors



By MATTHEW L. WALD



March 26, 2002 - Nuclear reactor operators have been ordered to check 

their reactor vessels after the discovery that acid in cooling water 

had eaten a hole nearly all the way through the six-inch-thick lid of 

a reactor at a plant in Ohio. The corrosion left only a stainless-

steel liner less than a half-inch thick to hold in cooling water 

under more than 2,200 pounds of pressure per square inch.   



At the 25-year-old Ohio plant, Davis-Besse, near Toledo, the 

stainless steel was bent by the pressure and would have broken if 

corrosion had continued, according to the Nuclear Regulatory 

Commission, where officials were surprised by the discovery. They 

said they had never seen so much corrosion in a reactor vessel.  



The commission, which has warned plants for years to watch for any 

corrosion, has ordered all 68 other plants of similar design ? 

pressurized-water reactors ? to check their lids. The commission is 

particularly worried about a dozen of the oldest plants and ordered 

them to report by early April whether they were safe enough to keep 

in service. The commission told these plants to demonstrate that 

technicians there would have noticed such corrosion in their normal 

inspections, had it occurred.  



If the liner had given way in the Ohio reactor, experts say, there 

would have been an immediate release of thousands of gallons of 

slightly radioactive and extremely hot water inside the reactor's 

containment building.  



The plants have pipe systems that are meant to pump water back into a 

leaking vessel, but some experts fear that if rushing steam and water 

damaged thermal insulation on top of the vessel, the pipes could 

clog. In that event, the reactor might have lost cooling water and 

suffered core damage ? possibly a meltdown ? and a larger release of 

radiation, at least inside the building.  



Such extensive corrosion "was never considered a credible type of 

concern," said Brian W. Sheron, associate director for project 

licensing and technology assessment at the regulatory commission.  



Small leaks of cooling water are common, Mr. Sheron said, but 

engineers always thought that if cooling water leaked from the piping 

above the vessel and accumulated on the vessel lid, the water would 

boil away in the heat of over 500 degrees, leaving the boric acid it 

contains in harmless boron powder form. At Davis-Besse, however, it 

appears that the water was held close to the metal vessel lid, or 

head, perhaps by insulation on top of the vessel.  



Boric acid is used in cooling water to absorb surplus neutrons, the 

subatomic particles that are released when an atom is split and go on 

to split other atoms, sustaining the chain reaction.  



Engineers are not yet certain why the corrosion occurred.



A nuclear engineer at the Union of Concerned Scientists, a nonprofit 

watchdog group that is often critical of the Nuclear Regulatory 

Commission, said the discovery was troubling.  



"This is really something that shouldn't happen," said the engineer, 

David Lochbaum. "You shouldn't get such a huge hole in a pressure-

retaining vessel."  



Edwin S. Lyman, the scientific director of the Nuclear Control 

Institute, an anti-proliferation group based here, said: "This is a 

pretty serious issue, and it has generic implications. And it was 

discovered by accident."  



Workers stumbled on the problem in the process of fixing a leaking 

tube that connects to the vessel head, which is 17 feet in diameter 

and weighs 150 tons. The tube is part of the reactor control system; 

inside it there is a control rod, which operators can lower into the 

core to smother the flow of neutrons and stop the chain reaction, or 

raise to allow the reactor to run.  



Technicians discovered that the metal that supports the tube had 

mostly disappeared.  



The plant owner, FirstEnergy Corporation, is hoping to patch the 

hole, an irregular opening about 4 by 5 inches. But the commission is 

skeptical about whether this is possible.  



No one in this country has replaced a reactor vessel head, although 

several plants have ordered parts to do so. FirstEnergy ordered a new 

head just before the extent of the problem became obvious. A company 

spokesman said the company hoped to install it in the spring of 2004.



That date reflects how the industry, with no new reactor orders in 

decades in this country, has limited production capacity for such 

parts.  



The plant might also be able to use a vessel head from a reactor in 

Midland, Mich., that was never completed, or from a similar plant 

that was retired in 1989.  



Davis-Besse, which began operating in 1977, was not designed with the

idea that the head would be replaced; technicians would have to cut a

bigger hole in the steel-reinforced concrete containment building to

get the new head into it.



The company has not said what the job will cost, but Duke Power 

Company, which operates three reactors similar to Davis-Besse, plans 

to replace the heads of all three for about $20 million. FirstEnergy 

could spend nearly that much each month for electricity from 

alternative sources if it must wait for the replacement part.  



Because of the discovery at Davis-Besse, the regulatory commission 

ordered a dozen other plants to report back within two weeks and 

prove that inspections they have done in the past would have found 

any corrosion.  



The inspection cannot be done while the plant is running, and if the 

utilities cannot convince the commission, they presumably face 

shutdowns of perhaps several weeks just for the checks.  



Such shutdowns occurred intermittently in the 1970's and 80's but 

have become extremely rare as reactors have improved their 

reliability.  



The industry is hopeful, however, that inspections it began under 

commission orders several years ago, to look for leaks, would have 

found any similar cases. Those inspections began after the heads of 

French reactors showed signs of leaks and corrosion.  



"It could be something unique to Davis-Besse," said Alexander Marion, 

director of engineering at the Nuclear Energy Institute, the 

industry's trade association. A goal for the investigation at the 

plant, he said, would be to find out not only why the corrosion 

occurred but also why it was not noticed sooner.  



"The plants are getting older and we're starting to see these kinds 

of problems," Mr. Marion said.  



-------------------------------------------------

Sandy Perle

Director, Technical

ICN Worldwide Dosimetry Service

ICN Plaza, 3300 Hyland Avenue

Costa Mesa, CA 92626



Tel:(714) 545-0100 / (800) 548-5100  Extension 2306

Fax:(714) 668-3149



E-Mail: sandyfl@earthlink.net

E-Mail: sperle@icnpharm.com



Personal Website: http://sandy-travels.com

ICN Worldwide Dosimetry Website: http://www.dosimetry.com








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