davis bessie messie details emerge

[Norman Cohen <ncohen12@comcast.net>]

Raymond Shadis wrote:



> Thanks to Anne D Burt, Friends of the Coast,  for sending this article

> on.

> FYI-  More DETAILS EMERGE on DAVIS-BESSE.  This is the first article

> I've seen where the reactor pressure vessel head  material remaining

> at the base of the corroded hole is properly identified as, cladding.

> At Maine Yankee ( and it may be for Davis-Besse, as well) the interior

> of the reactor was coated with stainless steel by running bead after

> bead of  stainless steel arc-weld around and around the inside surface

> of the vessel, like coil-made pottery, until the surface was covered

> with the requisite thickness (about 3/8". Each pass of the welder

> requires cleaning and inspection before the next pass so to insure

> that the bead is continuous, contains no bubbles or slag,has a surface

> free of slag, and is uniformly melted into the beads of weld below and

> along side of the new bead. There are thousands of opportunities to

> include and cover flaws. While such flaws provide starting places for

> tears, cracks, or corrosion, not-to-worry because cladding is not

> meant contain pressure and it may be that credit for the strength of

> cladding is not  taken in pressure vessel analysis.  However, with the

> pressure vessel gone, the "built-up" character of cladding must, it

> seems to me, says something about depending on the strength and

> durability ( including sensitization and stress corrosion cracking) of

> the remaining material- stainless stel or no, relatively small

> cross-section or no.  Ray  U.S. Questions Nuclear Plant's Repair Plan

> April 11, 2002

> By MATTHEW L. WALD

>

> BETHESDA, Md., April 10 - Officials from an Ohio nuclear

> power plant assured federal regulators today that they

> could repair corrosion that had eaten nearly all the way

> through a reactor lid, but faced a barrage of questions

> from the Nuclear Regulatory Commission staff.

> Executives of the Davis-Besse nuclear plant near Toledo met

> with commission officials to convince them that they could

> repair the hole by filling it with a 13-inch stainless

> steel disk, welded into place.

>

> After a three-hour meeting, the executives left with a long

> list of questions to answer, including how they would make

> sure that the heat of a welder's torch would not further

> damage the metal.

> Sixty-eight other reactors around the nation have a design

> similar to Davis-Besse's, and the commission is trying to

> determine if any of them have incurred the same kind of

> corrosion. All 68 have said they did not, but some did not

> provide enough of a basis for their assurances, said Ken

> Karwoski, a corrosion specialist with the commission.

> At Davis-Besse, which is owned by the FirstEnergy

> Corporation of Akron, Ohio, cooling water from the reactor

> leaked from nozzles on the reactor head; boric acid, which

> is mixed into the water to control the nuclear reaction,

> ate away about 70 pounds of metal, going through six inches

> of exterior steel.

> When the 25-year-old reactor was shut for refueling and

> repair of the nozzles this year, all that was left was a

> thin layer of steel meant to control corrosion inside the

> vessel.

> The regulators were shocked by the extent of the corrosion.

> Leaks were well known, but government and industry

> officials believed that when they occurred, the temperature

> at the vessel head, more than 600 degrees, would boil the

> water away and leave nothing but a harmless boron powder.

> After investigating, the commission staff concluded that

> the Davis-Besse operators had missed many opportunities to

> find the problem before it became so serious.

> Critics of nuclear power agreed.

> "When you're using a

> crowbar to knock the stuff off the reactor head, it's a

> sign you've gone too far," said David Lochbaum, a nuclear

> engineer with the Union of Concerned Scientists. Workers

> had pried boric acid off the head during a refueling

> shutdown in 2000.

> At the meeting today, about a dozen commission staff

> members asked about the "repair concept" that company

> officials presented.

> "It's a first-of-a-kind repair," said Brian W. Sheron,

> associate director for project licensing and technology

> assessment at the commission. "The staff is very concerned

> that whatever we approve, they are confident it is going to

> hold up."

> One issue, Mr. Sheron said, was "just the sheer size of the

> weld" - to hold in place a piece 13 inches in diameter and

> about 6 inches thick.

> FirstEnergy officials said the session had given them a

> clear indication of what information their plan would need

> to include to satisfy the commission. The company had hoped

> to submit that plan next week but company executives said

> after the session that it might take longer.

> If contractors cannot repair the vessel head, the company

> plans to replace it with the head from a reactor in

> Midland, Mich., that was abandoned during construction, or

> the head of a retired plant in Sacramento. They have also

> ordered a new reactor head, but do not expect delivery

> before February 2004.

> Delays are expensive because the plant employs 780 people,

> whether or not it generates electricity; property taxes

> alone run $500,000 a month. Officials hope to have the

> reactor running by summer.

> Opponents say that would be too soon. Christine

> Patronik-Holder, a spokeswoman for the Safe Energy

> Communication Council, said that until everyone agreed on

> exactly how the corrosion occurred, "plans to place patches

> amount to little more than Russian roulette with the lives

> of northern Ohioans."

> But the company is proceeding to figure out repair details,

> including how it will check for leaks when the work is

> completed.

> Radiation dosage in the repair area is so high that a

> welder would absorb in two hours as much radiation as the

> industry usually allows workers to incur in a year. In two

> and a half hours, the welder would reach the annual limit

> the commission sets. So the plan will rely on robot

> welders.

> Indeed, radiation in the affected area is so high that it

> will be a challenge just to X-ray the completed repairs to

> look for any flaws. Framatome, the French reactor company

> that will do much of the work, said it could compensate for

> the high background radiation.

>

> ttp://www.nytimes.com/2002/04/11/national/11NUKE.html?ex=1019720794&ei=1&en=9453952ea2027cca



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