OHIO Nuclear Plant - Corrosion

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FWD: from RTK

http://www.commondreams.org/headlines02/0326-04.htm

U.S. Orders Checks for Corrosion at Nuclear Reactors

by V. Wald

WASHINGTON, March 25 — 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, -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 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 -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,

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.

-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 -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 -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 -Besse, " said n,

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. n said.

Copyright 2002 The New York Times Company