ML20040D736

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Provides Info Re Gouges Found in Torus & Final Plans to Implement Repair & Repair Insp of Gouges,Per NRC 811218 & 820105 Requests
ML20040D736
Person / Time
Site: Pilgrim
Issue date: 01/26/1982
From: Deacon W
BOSTON EDISON CO.
To: Vassallo D
Office of Nuclear Reactor Regulation
References
82-26, NUDOCS 8202020204
Download: ML20040D736 (2)


Text

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EOSTON EDISON C OMPANY ano Bonetow 5,asse BOSTON. MAssAcMustTTs 02199 January 26, 1982 BEco. Ltr. #

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Mr. Domenic B. Vassallo, Chief 2 #

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Operating Reactors Branch #2  % 7 Division of Licensing -3 Office of Nuclear Reactor Regulation t, U.S. Nuclear Regulatory Commission

  • y Washington, D. C. 20555 m License No. DPR-35 Docket No. 50-293 Torus Gouges Report

References:

(A) Meeting between NRC and Boston Edison, December 18, 1981 (B) Meeting Sunmary dated January 5,1982 from Mr. K. T. Eccleston to .

Mr. T. A. Ippolito

Dear Sir:

In References (A) and (B), the NRC requested Boston Edison to supply information concerning gouges found in the torus, and to describe the final plans to imple-ment repair and repair inspection of these gouges. We believe that this submittal satisfies the requests contained in the above references.

Description On November 10, 1981, following the saildblasting of the torus inner shell in preparation for painting, six localized gouges were identified in torus bay eleven. The discovery of these gouges was reported in Licensee Event Report 81-061/01T-0, Boston Edison letter number 81-270. The deepest gouge was .600 inch at its maximum depth, and the diameter ranged from 1.250 to 1.625 inches. /

At the location of the deepest gouge, the torus shell is .6875 inch thick. .$

Cause , p We believe the most probable cause of the gouges was carbon arc gouging, which most likely occurred during the 1980 refueling outage. In addition, we imposed the most conservative repair requirements by postulating a thermal process of gouginc Sj2020pkoffff26 P ADOC ~

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,r' Mr. Domenic B.- Vassallo, Chief January 26, 1982 Page 2 Torus ' Failure Analysis Employing shell loads based on the results of the Mark I Containment Long Term Program, the d.eepest gouge in the shell was analyzed using fracture mechanics and elastic techniques. The results of this analysis, provided by Teledyne Engineering Services, Inc., demonstrate that the suppression chamber shell would have remained intact under worst case LOCA (DBA) conditions, and that a shell . leak would not have resulted under such conditions during Fuel Cycle #5.

Repair Weld repairs to the damaged areas will be made using the butterbead/temperbead technique per the requirements of ASME Code Section XI and ASME Code Case N-236.

NDE/ Testing ,

The damaged areas will be examined by the magnetic particle method prior to weld repair. Final examination of the repaired areas will be by radiography and magnetic particle methods, and will be performed 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> a.fter the welded area is at ambient.

A leak rate test in accordance with 10 CFR 50, Appendix J will be performed after repairs are made.

Inspection / Surveillance Prior to the resumption of power operation, the torus shell will be visually inspected in conformance with the requirements of ASME Section XI. The accept-ance criteria for shell defects will be as described in the Owner Specification for Pilgrim Nuclear Power Plant Structural Modification to the Mark I Containment Torus Support System. Also, a surveillance procedure will be imolemented to inspect the torus shell whenever any work with the potential to cause shell damage is done in or around the torus.

Boston Edison believes that the information supplied above satisfactorily describes the gouging issue and its related corrective actions. Should you require further information concerning this issue after reviewing this submittal, please contact us.

Very truly yours, /7 l '

C F A --

' d. H. Deacon, Acting Manager Nuclear Operations Support Dept.