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Updated Tuesday, March 19, 2002
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Posted on Tue, Mar. 19, 2002 story:PUB_DESC
Second cavity at reactor
Hole found on safety device at Davis-Besse plant; initial damage more widespread

Beacon Journal business writer

A second cavity, apparently caused by acid corrosion, has been found on a critical safety device at FirstEnergy Corp.'s shut-down Davis-Besse nuclear power plant.

The U.S. Nuclear Regulatory Commission also said damage from the first hole found at the plant earlier this month has spread more than earlier thought.

Additionally, a FirstEnergy spokesman said even more damage could be found as plant inspections continue.

The latest cavity, on a massive structure called the reactor vessel head, appears to be about 1 inches deep into the 6 3/8-inch-thick carbon-and-stainless-steel structure that covers the radioactive fuel core.

The NRC announced late Friday the discovery of a second small area of corrosion on the reactor vessel head, about 1 inches by 3/16 of an inch.

A closer examination of the second area of corrosion found the 1 -inch-deep cavity, NRC spokesman Jan Strasma said. He described this second cavity as ``much less significant and much smaller in size'' than the first hole.

``It did not go all the way down,'' he said.

The first cavity, discovered earlier this month, is about 6 inches deep. The Akron utility last week estimated that repairing the first cavity would cost between $5 million and $10 million and push back restarting the nuclear plant until the end of May or June. Each month the 883-megawatt nuclear power plant is down will cost the utility between $10 million and $15 million a month in additional energy costs as well. FirstEnergy had planned to restart the plant, in Oak Harbor about 25 miles east of Toledo, at the end of this month.

FirstEnergy stock has fallen 9.3 percent since the initialDavis-Besse problems were revealed publicly.

It's too early to say how much more, if any, this smaller cavity will cost FirstEnergy, said Davis-Besse spokesman Richard Wilkins. He said late yesterday that he hadn't been told about the second cavity.

``I wouldn't dispute it,'' Wilkins said. ``They are working constantly on this thing. The information will come out a little at a time.''

The newly discovered cavity is next to a device called a vessel head penetration nozzle that has hairline cracks in it. The Davis-Besse plant has 69 of those nozzles on top of the reactor vessel head. They are used to control the nuclear reaction; five nozzles were found with cracks in them.

Three of those damaged nozzles apparently allowedboron-infused water to leak through and touch the vessel head's carbon steel exterior. The two cavities were discovered at two of the three leaking nozzles.

The first cavity that FirstEnergy reported finding ate all the way through the vessel head's carbon steel, only to be stopped when it ran into a thin layer of stainless steel that lines the interior.

Safety systems would have shut the reactor down immediately if the acid ate a hole all the way through the reactor vessel head and allowed superheated coolant to escape, officials said last week. The coolant around the fuel core is 600 degrees Fahrenheit and at a pressure of 2,500 pounds per square inch. No radiation would have leaked into the environment, officials said.

The NRC also reported that the boric acid, a byproduct of the nuclear reaction, apparently began eating away, or ``undercutting,'' additional carbon steel as it spread out along the stainless steel lining at the location of the initial cavity. Strasma said the ongoing investigation into the reactor damage hasn't shown how far the undercutting spread, although FirstEnergy estimates about 40 pounds of steel was eroded.

The damage was first discovered through ultrasonic tests.

More will be known about the second cavity after FirstEnergy employees remove the damaged nozzle that rests next to it, Wilkins said. The 3- to 4-foot-long nozzle could take weeks to remove, he said.

Each nozzle is made of stainless steel and weighs 150 pounds, he said. The nozzles are actually larger than the holes they fit into, he said. The devices have to be frozen so that they contract and slip in. Warming up expands the steel to create a tight fit, and then it is welded into place, he said.

``They have to machine it out of there'' using robotic equipment, Wilkins said. ``The work on the (vessel) head is a high priority item. We're not going to have a really good handle on the corrosion issue until we remove the nozzle. It's not going to be an easy thing to do.''

A team of 50 nuclear power experts is working to figure out how the 150-ton reactor vessel head was damaged and ways to safely repair it and get the plant running again. The initial damage was found after the plant was shut down in mid-February for refueling. The NRC mandated safety inspections at other nuclear plants similar in design to Davis-Besse after nozzle cracks were first discovered in 2000 and 2001 at a South Carolina plant complex owned by Duke Energy.

Davis-Besse is the first plant to report finding cavities that apparently were caused whenboron-rich water leaked through the nozzle cracks and touched the vessel head's carbon steel.

It's possible that the problems at Davis-Besse will result in further inspections at other nuclear power plants in the country, NRC officials have said.


Jim Mackinnon can be reached at 330-996-3544 or jmackinnon@thebeaconjournal.com
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