DB vessel head had hairline surface cracks

[Norman Cohen <ncohen12@comcast.net>]

Bill Corcoran wrote:



> Dave, I have pasted a section from an ANS e-mail below.Best

> Regards, Bill Corcoran W. R. Corcoran, Ph.D., P.E.

> Nuclear Safety Review Concepts

> 21 Broadleaf Circle

> Windsor, CT 06095-1634

> 860-285-8779 Fax:

> 702-993-2408r??????????????????????????????????????????????????????????????????????????? DAVIS-BESSE'S

> VESSEL HEAD HAD HAIRLINE SURFACE CRACKS, researchers found

> while examining a sample section of the head's steel liner. The

> research

> was commissioned by FirstEnergy Nuclear Operating Company (FENOC), in

> conjunction with the Nuclear Regulatory Commission. Investigation of

> the

> 17-in.-diameter sample revealed that the cracks were about 3Z8-in.

> long

> (depth not yet known), and were located near the center of the liner

> that

> was exposed when boric acid corroded the vessel head's carbon steel.

> Researchers also determined that the average thickness of the liner in

> the

> sample was 0.256 in., ranging from a minimum of 0.202 in. to a maximum

> of

> 0.314 in. Discovery of the hairline cracks was announced by FENOC on

> September 11.

>    FENOC noted that the stainless steel liner held full pressure--2155

>

> pounds per square inch--during normal operation of the plant, despite

> the

> presence of the cracks and boric acid corrosion on the vessel head.

> The

> latest research findings will be used to recalculate how much more

> pressure

> the liner could have withstood, FENOC added.

>    Additional research on the sample uncovered a number of lateral

> cracks

> in the remaining portion of the control rod drive mechanism nozzle, as

> well

> as a partial circumferential crack around the welded area on the lower

> part

> of the nozzle. The crack did not penetrate the weld or the vessel

> head,

> which confirmed previous testing done on the head, according to FENOC.

>

>    As research continues on the sample section, FENOC is preparing to

> install a replacement vessel head (from the canceled Midland plant, in

>

> Michigan) that has been moved inside Davis-Besse's containment

> building.

> Davis-Besse, an 873-MWe (net) Babcock & Wilcox pressurized water

> reactor,

> is located in Oak Harbor, Ohio.

>    Davis-Besse has not operated since last February, when the plant

> was

> shut down to conduct nozzle inspections. In early March, inspection

> workers

> discovered the deep cavity in the vessel head. The cavity, the result

> of

> boric acid corrosion of carbon steel, was about 4 in. by 5 in. and

> approximately 6 in. deep, leaving only the stainless steel liner

> intact.

>

>

>

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