ML13308B448
| ML13308B448 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 10/03/1977 |
| From: | Head J SOUTHERN CALIFORNIA EDISON CO. |
| To: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| References | |
| NUDOCS 8103050927 | |
| Download: ML13308B448 (2) | |
Text
Southern California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE J. T. HEAD, JR.
ROSEMEAD, CALIFORNIA 91770 TELEPHONE VICE PRESIDENT October 3,1977 13-572-1472 U. S. Nuclear Regulatory Commission Region V I,
.\\
Walnut Creek Plaza, Suite 202 (Ap 1990 North California Boulevard I
CO Walnut Creek, California 94596 Attention:
Mr. R. H. Engelken, Direct Docket No. 50-206 San Onofre Unit 1
Dear Sir:
References:
(1) Letter from SCE (J. M. Curran) to USNRC Region V, dated September 19, 1977; Anti-vibration bar indica tions.
(2) Letter from SCE (J. G. Haynes) to USNRC, Director of Nuclear Reactor Regulation, dated February 4, 1977; Steam generator inspections.
(3) Letter from SCE (K. P. Baskin) to USNRC, Director of Nuclear Reactor Regulation, dated February 14, 1977; Steam generator inspections.
In accordance with the reporting requirements of Section 6.9.2 of Appendix A to the San Onofre Unit 1 Provisional Operating License, the following information and attached Licensee Event Report are submitted as follow-up to Reference 1.
Described herein are actions we are taking as a result of steam generator eddy current examinations which were con ducted during the September 9, 1977, maintenance outage.
In References (2) and (3),
we reported on our program of steam gen erator inspections, analyses, and anti-vibration bar (AVB) modifications performed during the October, 1976, refueling outage.
This program was concerned with the extent and effects of tube denting and with tube wear observed at interfaces of tubes with originally installed AVB's.
In con nection with the September 9, 1977, maintenance outage, we undertook a program of limited eddy current examinations and visual inspections to aid in assessing the progression of tube denting, including "hourglassing" of tube support plate flow slots, and in evaluating the effectiveness of the AVB modifications.
Regarding the denting investigation, 400 KHz reduced gain eddy cur rent examinations of approximately 120 tubes in each of steam generators A and C were conducted to assess the rate at which denting is progressing.
/O30s 1 09 L7
U. S. Nuclear Regulatory Commission Page 2 October 3, 1977 The tubes examined were located in the region of the centerline flow slots.
To determine whether minor cracking is occurring in small bend radius U-tubes, 100 KHz eddy current surveys of 120 tubes were conducted in steam generator C.
Lastly, photographs and videotapes were made of support plate flow slots in all three steam generators. The results of these examinations and inspections indicate that the extent and effects of denting following 142 effective full power days of operations are substantially unchanged from that reported during the past refueling outage.
Regarding the AVB investigation, approximately 140 tubes in each of steam generators A, B, and C had been initially selected for eddy current examinations. The tubes were selected from locations at the periphery of the tube bundles, in the critical flow triangles, and in the interior of the tube bundle at the innermost extent of the AVB's. Initial data from these examinations indicated that tube wear may be continuing at points of contact with the old AVB's. Consequently, the AVB investigation was expanded to include eddy current examinations of all tubes in each steam generator which are in contact with AVB's. In addition, a secondary side top entry was made into steam generator B to perform a visual inspection of the tube bundle and AVB's and to remove U-bend portions of three (3) tubes for metallurgical investigation.
The results of the above AVB investigations are being analyzed to deter mine the extent of tubes which continue to show wear at old AVB sites, the rate at which the wear is progressing, and the number of tubes to be plugged at this time. Our findings and proposed course of action are being docu mented for submittal to and approval by NRR prior to resumption of power operations at San Onofre Unit 1. Copies of all such documentation will be forwarded to your office for information and use.
Should you have any questions or require additional information con cerning the above, please let me know.
Attachment:
Licensee Event Report No. 77-13 cc: Office of Inspection & Enforcement Office of Management Information and Program Control