ML13308B517
| ML13308B517 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 05/12/1977 |
| From: | Head J SOUTHERN CALIFORNIA EDISON CO. |
| To: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| Shared Package | |
| ML13308B518 | List: |
| References | |
| IEC-76-06, IEC-76-6, NUDOCS 8103110068 | |
| Download: ML13308B517 (3) | |
Text
Southern California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE J. T. HEAD, JR.
ROSEMEAD, CALIFORNIA 91770 TELEPHONE VICE PRESIDENT may 12, 1977 213-572-1472 U. S. Nuclear Regulatory Commission Region V Office of Inspection and Enforcement Suite 202, Walnut Creek Plaza 1990 North California Boulevard Walnut Creek, California 94596 Attention:
Mr. R. H. Engelken Docket 50-206
Dear Sir:
IE Circular No. 76-06 Stress Corrosion Cracks in Stagnant, Low Pressure Stainless Piping Containing Boric Acid Solution at PWR's
Reference:
(1) Letter from SCE (J. B. Moore) to USNRC Region V dated December 23, 1976.
(2) Letter from SCE (J. T. Head) to USNRC Region V dated February 7, 1977.
(3) Letter from SCE (J. T. Head) to USNRC Region V dated March 2, 1977.
Reference is made to your correspondence of November 24, 1976, forwarding the subject circular. Reference (1) was our initial response to IE Circular 76-06, and described our program and schedule for assuring continued integrity of safety related piping systems which are not frequently flushed or contain non-flowing liquids. This letter provides a sumary report of the examinations and an evaluation of results as requested'.
The following examinations were conducted in response to the subject circular:
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- 1. Ultrasonic testing (UT) was conducted in accordance with the ASME Code,Section XI, through the Winter 1975 Addenda. Those Class 2 components, in systems where both design pressure and temperature are equal to or less than 275 psig and 200 degrees F respectively, were also included in this examination. Twenty-five percent of the total number of existing welds in the safety injection, recirculation and containment spray systems were ultrasonically inspected. This represents one-half of the Section XI requirements for a ten-year interval.
- 2. The residual heat removal system was visually inspected for leakage.
- 3. A hydrostatic test of the recirculation system was conducted in accordance with Section 4.3.111 of San Onofre Unit 1 Technical Specifications.
The results of these inspections disclosed no indications of defects similar to the failures identified in IE Circular 76-06. Specifically:
- 1.
The results of the ultrasonic examinations indicated that all welds were acceptable.
- 2.
No abnormalities were found during the visual inspection of the residual heat removal system.
- 3.
The hydrostatic test of the recirculation system was satisfactorily completed.
It should be noted that our current in-service inspection program is being modified to comply with the provisions of ASM4E Code,Section XI.
Under this program, surveillance of the aforementioned systems will be conducted on a continuing basis.
Station procedures were reviewed to ensure that all areas of the safety injection, recirculation, containment spray and residual heat removal systems are flushed at least at refueling intervals. In the past, the recirculation and containment spray systems have been flushed during normal refueling operations. However, a procedural change was made to document this activity and to ensure that all portions of these lines are flushed. The safety injec tion and residual heat removal systems have existing requirements for flushing stagnant pipe sections at least once during each refueling.
Reference (2) describes a through wall flaw found in the safety injection recirculation system during a visual inspection of the line. Metallurgical examination of the flaw and a review of the construction records indicated that the flaw occurred due to sensitization during pipe refabrication. This flaw was not similar to the defects identified in IE Circular 76-06. The sensitized pipe was subsequently replaced.
-3 Reference (3) reported two leaks noted during a hydrostatic test of the recirculation system. These leaks were located in the heat affected zone of welded joints. Metallurgical analysis showed that the welded joints had been sensitized to intergranular stress corrosion, probably due to the weld technique employed. The welding procedure used for the replacement pipe waa:
designed to limit the metal temperature during welding and thus eliminate the possibility of sensitization. Temperature sensing devices were used in the heat affected zone of the new welds and metal temperature limited to 350 degrees F. In addition, a welded joint intended for use in the replacement pipe was subjected to metallurgical analysis. The results of the analysis showed no signs of sensitization. The replacement pipe is fabricated from low carbon stainless steel instead of the original standard grade of stain less steel and is highly resistive of intergranular stress corrosion. In summary, the changes made in fabrication technique and metal composition have minimized the possibility of intergranular stress corrosion of this line. The recirculation line was replaced in its entirity and successfully hydrostati cally tested in accordance with Section 4.3.111 of San Onofre Unit 1 Technical Specifications.
This correspondence constitutes our final report on IE Circular 76-06.
Provided herewith is, additionally, an updated LER No. 77-04 as Reference (3) indicated would be provided.
Sincerely, Attachment cc:
Director, USNRC, Office of Inspection and Enforcement