ML13308B469
| ML13308B469 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 03/04/1977 |
| From: | Head J SOUTHERN CALIFORNIA EDISON CO. |
| To: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| References | |
| NUDOCS 8103060043 | |
| Download: ML13308B469 (6) | |
Text
Southern California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE J. T. H EAD, JR.
ROSEMEAD, CALIFORNIA 91770 TELEPHONE VICE PRES10ENT 213-572
-1472 March 4, 9 1
REGULA TO 0 b ET FILE C0 U. S. Nuclear Regulatory Commission REGION V Region V Office of Inspection and Enforcement Suite 202, Walnut Creek Plaza 1990 North California Boulevard Walnut Creek, California 94596 Docket No. 50-206 San Onofre Unit 1 Attention: Mr. R. H. Engelken, Director
Dear Sir:
Reference:
(1) Letter from SCE (Mr. H. L. Ottoson) to USNRC Region V, dated February 22, 1977 (2) Letter from USNRC (Mr. A. Schwencer) to SCE (Mr. Jack B. Moore) dated February 18, 1977 (3) Letter from SCE (Mr. K. P. Baskin) to USNRC (Mr. A. Schwencer) dated January 19, 1977.
(4) Letter from SCE (Mr. K. P. Baskin) to USNRC (Mr. A. Schwencer) dated February 4, 1977.
Reference (1) presented prompt notification of the failure of the containment integrated leak rate test due to two holes inadver tently drilled through the shell of the containment sphere. This letter constitutes the follow-up report submitted in accordance with the provisions of Section 6.9.2.a of Appendix A to the Provisional Operating License No. DPR-13.
On February 20, 1977, while conducting the containment Integrated Leakage Rate Test (ILRT), a leak of approximately one percent of the sphere volume in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> was noted. This is more than ten times the allowable measured leakage of.090 weight percent per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> established by Amendment No. 24 to the Provisional Operating License which was forwarded to SCE under the cover of reference (2).
pjo 36Mooo43
-2 During the unsuccessful ILRT, an examination of all penetrations in the sphere revealed no leakage. Records of work conducted during the course of the present outage were reviewed. This review indicatd that the anchor bolts for a new access platform inside the containment may have been placed close enough to the sphere shell for penetration to occur.
A segment of the sand transition zone on the west side of the sphere, adjacent to the new leak rate access platform was exposed to check for leakage through the containment shell.
After adding a soap and water solution to this area, air bubbles were observed and the sphere subsequently was depressurized.
Following the leak rate test, temporary shoring was installed to support the access platform. The concrete between the three outer support columns for the platform and the sphere shell was removed to expose the nine anchor bolts nearest the shell. These bolts are numbered sequentially one through nine as shown on Attachment 1.
Investigation revealed that cores 8 and 9 had penetrated completely through the sphere shell. Core 1 had made a scratch in the shell one inch long by one-eighth inch deep by one-fourth inch wide. The other six cores did not contact the sphere shell. The holes at locations 8 and 9 are approximately two inches in diameter.
The location of the holes in the sphere shell is about one foot below the sand transition zone. This sand filled annulus extends six feet from plant grade at elevation +20 feet down to elevation +14 feet and provides a transition zone from the rigid fixed foundation to the free standing portion of the sphere above grade. The sphere shell in this location is encased in concrete about two feet thick inside and six feet thick outside. Attachment 2 shows the arrangement of the containment sphere, sand filled annulus, and concrete foundation.
The installation of the new access platform, as described in Amendment 52 to the San Onofre Unit One Final Safety Analysis (FSA),
was performed in conjunction with the addition of several containment isolation valves both inside and outside the sphere.. In order to provide access for maintenance of these valves located inside the containment, the platform was installed on the west side of the sphere just to the north of the sphere east-west centerline. The supports for the platform consist of three existing columns and three new columns.
The three new support columns were founded on base plates at elevation
+14 feet. Each of the column base plates has six anchor bolts, which necessitated core drilling the concrete at elevation +14 feet. The construction drawing called for two inch diameter core drills to a depth of one foot each. The installation of these columns and the platform was completed according to plans in October 1976 and the two holes through the containment shell were unknowingly cored at that time.
-3 A review of the facts surrounding this incident revealed the following:
A design oversight occurred in that the applicable construction drawings did not adequately detail the proximity of the sphere shell and anchor bolt locations.
A work procedure adequately controlling concrete core drilling was not prepared.
Quality assurance hold points were not used at the time of core drilling to measure hole depth inspect the removed core for indications.
The inspection that was performed occurred after the column base plates were placed on the concrete ledge and was intended only to check the bolt holes ready for grouting.
Thus this inspection was ineffective in detecting problems associated with core drilling.
To prevent a recurrence construction procedure(s) will be prepared defining necessary controls for concrete core drilling. This procedure(s) will require an engineering evaluation of abnormalities that could be expected during core drilling. Detailed section sketches of the area to be core drilled will be required. Quality control hold points for inspection will be designated, including measurement of hole depth and inspection of removed cores. If deviations from the engineering evaluation are encountered, drilling will be stopped until engineering and construction management have dispositioned the matter. If these administrative requirements had been in effect during the previous core drilling, this incident would not have occurred.
The repair procedure for the sphere has been reviewed and approved by the ASME Code Jurisdictional Authority, State of California Division of Industrial Safety, and the ASME Code Authorized Inspector, as required by Article IS-413 of Section XI of the ASME Boiler and Pressure Vessel Code. Further, stresses in the area of the repair at the peak contain ment pressure identified in enclosure (1) to reference (3) remain below code allowables given in enclosure (2) to reference (4).
All of the three affected areas will be cleaned and dye penetrant tested prior to repair. The two holes will be plugged with 1-1/2" nominal pipe, ASME SA 106 Schedule 160. The pipe will be attached to the shell with a 1/2" fillet weld by shielded manual arc welding (SMAW) using low hydrogen weld rod. Dye penetrant examinations will be performed on the root pass, midway, and the completed weld. Epoxy will be in the cavity and placed beneath the two sphere holes and in the repair pipe down to the foundation to provide corrosion protection. The pipe will be threaded and a cap will be screwed in and seal welded. The completed repair will be vacuum box tested to ensure leak tightness. The scratch on the surface at core 1 will be repaired with weld buildup by SMAW using low hydrogen weld rod. The final overlay will be ground flush to the surface.
-4 No further concrete core drilling is planned for the present outage.
It is anticipated that the administrative changes described above will be complete in April 1977.
Sincerely, Attachments: (1) Leak Rate Platform Anchor Bolt Location Key Plan (2) Containment Sphere Foundation Layout (3) Licensee Event Report No. 77-05 cc:
Director, USNRC Office of Inspection and Enforcement Director, USNRC Office of Management Information and Program Control (MIPC)
ATTACHMENT 1 2
3 4
5 6
7 3
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9 10 12 23:
133 14
' 5 16 17 CO L
18
- 19.
COiNTA/MMEA1T 20 21 22 24 24 Rg1<p476 P6WAL4TFORM A7/CHOR o506 oc /O,470/VAk<
26 27 28 29CN~e
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ID/L 30 31 32 33 34 35
ATTACHMENT 2 SAND CONTAINMENT
/
ANNULUS SPHERE PLANT Diameter 140' GRADE
-I EL20'O" CONCRETE 2"0 HOLE I
EL 1M'O" 2
6 CON-CONCRETE CRETE /
INSIDE SPHERE EARTH 1.04" 6zFor Information Only 141S 2-28-7 LocatieSAN UNUFRE UNIT QNE CONTAINMENT SPHERE FOUNDATION LAYOUT -
BELOW No.
Revions
-LEAK RATE ACCESS PLATFORM Approved O.K.
O.K. Ckd. Made.O.
No. Date Southem Calima Edison FAMR
!) FORM NO.
ENO. 87 Approved I O.K. I O.K.
Ckd. IMade Approved I O.K.
O.K. Cd. 1 Mael Appoved I.K. O.K. Cd. Mde