ML20087B787

SR-S1-75-06:on 751021,discovered Tube R19C74 Severely Distorted & Stretched During Removal of Tube Sample on Steam Generator A.Caused by Malfunction of Internal Tube Cutter. Tube Plugged as Precautionary Measure

ML20087B787
Person / Time
Site:	Surry
Issue date:	11/26/1975
From:	Stallings C VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Moseley N NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
SR-S1-75-06, SR-S1-75-6, NUDOCS 8403090365
Download: ML20087B787 (6)

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V im x s A E x.iurritIG AND l'O W IMC C O, mea N y It ir.n u un n.Vdco r n :A 2 :8 H Cl ,

'Novenber 26, 1975 c

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!!r. Norman C. Moseley, Director - - . Serial No. 792 OEfice of Inapection and Enforcement POLM/.1Til: nl.w U.S. Nuclear Regulatory Commlucion Penion 11 - Suite 818 Dochet Ho. 50-280 230 Peachtree Street, Northwcut License No. DPR-32 Atlanta, Georgia 30303

Dear Mr. !!occicy:

The Virginia Electric and Peuer Company hereby uubmits forty (40) copics of Special Report Mo. SR-SI-75-06 descrLbing a recent evcut uhich occurred at the Surry Power Station, Unit No. 1.

The substance of this report' has been rev.iewed by both the Station '

Huclear Safety and Operating Comittec and the Syntem Nec1 car Safety and Operating Connittee. In addition, t.he Safely Revica Coasittcc of the Westinghouce F,lectric Corporation has reviewed the matter.

Very truly yours,

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G , ' :,< ('. L.ukiG,a v;*7 C. M. Stallings Vice President-Power Supply and Production Operations Lne}onuro cc: lir. Robert W. Reid 39 copica SR-Sl-75-06 1

13G43 8403090365 751126 PDR ADOCK 05000 ,

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SPECIAL REPORT SR-SI-75-06 i STEAM GENERATOR TUBE >

PULLING ACT1.VITIES NOVDiBER 25, l'975 DOCKET No. 50-281 LICENSE NO. DPR'-32 SURRY POWER STATION VIRGINIA ELECTRIC AND POWER COMPANY 4

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. 1. ItnRODUCTION . .

As a part of an. investigative p'ogram r to assist in analyzing generic steam generator tubo concerns, a tube was to be cut and removed from the "A" steam generator of Unit No. 1 at the Surry Power Station. During the activities associated with the tube removal on October 21, 1975, equipment failure allowed a etcan generator tube to be pulled without being cut prior to pulling. The purpose.of this report is to summarize the occurrence and the corrective actions associated therewith.

II. Sum 1ARY OF GC__C_URRCMCE A tube sampic was being removed from "A" stcam generat'r o on October 21, ,

1975 by representatives of the Uestinghouse Electric Corporation. The tube pulling operation concists of the following basic steps:

1. Counterbore the tube end to remove the tube to tube sheet weld.

2. Core drill the tube to relicyc the rolled portion.

3. Expand the tube into the sixth nupport plate.

4. Cut the tube with the I.D. fly cutter just below the sixth support plate.

5. Cut thtands into the tube I.D. with tap.

6. Install threaded pulling bar into tube.

7. Extract ' tube with hydraulic jacking equipment.

Upon completion of the above operations for tube R20C74, it was discovered that the tube was never-ly distorted and stretched. It appeared that the tube had not been cut, but had been pulled apart.

Subsequent investigation of the incident confirmed that the tube had not been cut, but was pulled apart by the hydraulic jacking mechanism. A

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O O review of the work log indicaten the aforementioned steps had been com-pleted. llowever, l't wau determinell that step number 4, cutting the tube, i

wan not natinfactorily completed.

Following the incident it wan determined that one of the extennion links which connected the cutting head to the drive nosembly had broken.

This failure renulted in the rotation'of oply that portion of the cutter acuembly below the broken link. Since the fly cutter in at the top o'f the act,embly, it in postulated that rotation did not occur and the tube was not cut. The WenLinghouse representative operating the cut,ter was not aware of t.he condition, nince the cut in made primarily by " feel" and the extended length of the antembly (about 26 Icet) resulted in 1cna nennitivity.

The operator assumed the tube had been cut and the operation continued and the i -

tube;was extracted with the hydraulic jaching equipment. Sufficient forco I

was applied by the jacking equipment to pull the tube apart.

i An a result of the occurrence, an inventigation van conducted to determine the cauce and consequencen of the event. The results of the investigation and corrective actionn are cummarized below:

1. Tube cutting activities

n. there was no damage to cutter heads

b. the linkage was broken on cutter assenbly

c. innpcction of the tube indicated it had not been cut

d. the tube cutting proceduro as written wan followed.

2. It la believed'that the tube parted approximately nine (9) inchen above the seventh (top) support plate. The location of the

'.rcak cannot be measured with precioion due to the plastic deformation of the removed segment.

3. The most probabic site for damage resulting from the high pulling force would be tube R19C74 which in directly below the broken

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o O O U tube. An uddy current probe was inserted through the outlet (cold Icg) of this tube and. pushed through the U-bend around to the' straight hot leg. No abnormal signals were observed in tube R19C74. inaddition,alltheothertubesincolumn 74 below row 20, as well as columns 73 and 75, were cddy current

. inspected to the fullest extent possible. There was some inter-forence with the eddy current probd associated with " denting" deformation at support plates on some of these tubes. It is concluded that the load imposed on tube R19C74 during the ,

pulling of tube R20C74 (above it in the U-bend section) did not result in significant deformation. It is considered that the l tubes below R19C74 were relatively unaffected if any contact I

did occur. .

4l. Tube R19C74 uns plugged as a precautionary measure.

l S. The remaining portion of tube R20C74 was plugged as well as the tube hole in the tube sheet from which the tube was removed.

Tubes surrounding R20C74 were also plugged. Westinghouse advises that the broken end of R20C74 cannot contact other tubes which form a part of the reactor coolant pressure boundary during subsequent operation.

6. The load imparted to the tube sheet during pulling operations was analyzed. The recorded maximum pulling force of 14,115 perads had no adverse effect on the integrity of the tube sheet or divider plate since the resulting deficctions are negligibic.

7. To preclude the recurrence of a similar event, the tube pulling procedure han been revised to require that an cddy current inspection be conducted on the tube. to be removed to confirm it has been cut.

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Ill. COMC1,USION Tube R20C74 was pulled apart in the removal operation as a result of an undetected ualfunction of the internal tube cutter which failed in a manner which gave the operator a false indication of having cut com-pletely through the tube wall.

'Ihc Inadvertant pulling of uncut iube R20C74 did not affect the structta -1 inteprity of the reactor coolant systen pressure boundary 'in steam nonerator "N'. The plugging of the tubes surrounding R20C74 pro-viden additional assurance that the integrity of the pressure boundary will be maintained. The loss of primary flow area in the tube bundic does not affect the operation of the safety injection system, nor will it interfere with nortn1 operation.

The hcalth and safety of the general public was not affected by the occurrence described herein. I 1

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