ML13302B811
| ML13302B811 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 11/06/1991 |
| From: | Rosenblum R SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML13302B812 | List: |
| References | |
| NUDOCS 9111120269 | |
| Download: ML13302B811 (3) | |
Text
ACCELERATED DISRIBUTION DEMONSTRTION SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)
ACCESSION NBR:9111120269 DOC.DATE: 91/11/06 NOTARIZED: NO DOCKET #
FACIL:50-361 San Onofre Nuclear Station, Unit 2, Southern Californ 05000361 50-362 San Onofre Nuclear Station, Unit 3, Southern Californ 05000362 AUTH.NAME AUTHOR AFFILIATION ROSENBLUM,R.M.
Southern California Edison Co.
RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)
SUBJECT:
Forwards RCE-91-025, "MSIV 2HV8204 Rail/Skirt Failure,"
safety engineering root cause rept.
D DISTRIBUTION CODE: A001D COPIES RECEIVED:LTR _ENCL _
SIZE: OZI iv D
TITLE: OR Submittal: General Distribution S
NOTES:
/
RECIPIENT COPIES RECIPIENT COPIES A
ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD5 LA 1
1 PD5 PD 1
1 D
KOKAJKO,L.
2 2
INTERNAL: ACRS 6
6 NRR/DET/ECMB 7D 1
1 D
NRR/DET/ESGB 1
1 NRR/DOEA/OTSB11 1
1 NRR/DST 8E2 1
1 NRR/DST/SELB 7E 1
1 S
NRR/DST/SICB8H7 1
1 NRR/DST/SRXB 8E 1
1 NUDOCS-ABSTRACT 1
1 OC/LFMB 1
0 OGC/HDS3 1
0 7ILE 01 1
1 RES/DSIR/EIB 1
1 4
EXTERNAL: NRC PDR 1
1 NSIC 1
1 R
I D
S A
D D
NOTE TO ALL "RIDS" RECIPIENTS:
S PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 20079) TO ELIMINATE YOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!
TOTAL NUMBER OF COPIES REQUIRED:
LTTR 24 ENCL 22
Southern California Edison Company 23 PARKER STREET IRVINE, CALIFORNIA 92718 R. M. ROSENBLUM November 6, 1991 TELEPHONE MANAGER OF (714) 454-4505 NUCLEAR REGULATORY AFFAIRS U. S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555
Subject:
Docket Nos. 50-361 and 50-362 Root Cause Evaluation of Main Steam Isolation Valves San Onofre Nuclear Generating Station, Units 2.and 3 Gentlemen:
As indicated in SCE's letter dated September 24, 1991, during an inspection of the Main Steam Isolation Valves (MSIVs) on San Onofre Unit 2, damage was identified in MSIV 2HV8204. The damage was observed in an internal cam assembly which is not part of the valve pressure boundary.
This letter provides our evaluation of the root cause of that damage in the enclosed report, "MSIV 2HV8204 RAIL/SKIRT FAILURE, ROOT CAUSE EVALUATION RCE-91-025, NOVEMBER 5, 1991."
As indicated in the enclosed report, it is concluded that the root cause of the observed damage to 2HV8204 was a poor design choice for the material used on the contact surfaces of the guide rail and shoe of the cam assembly. The material problem was compounded by a previous valve modification which resulted in line contact between the surfaces of these components and therefore increased the contact stresses between the components.
In order to eliminate the possibility of damage, both of the Unit 2 MSIVs have been modified during the current outage by hardfacing the components and revising the ramp angle between the contact surfaces. The Unit 3 MSIVs will be similarly modified during the next refueling outage, presently scheduled for January 1992. Until the Unit 3 refueling outage, it is concluded that the Unit 3 MSIVs remain capable of performing their safety function as discussed in the operability assessment forwarded by our September 24, 1991, letter.
Finally, SCE will perform a review of the design of all WKM valves used in safety related applications and determine if they are subject to similar failure modes.
It is expected that this review will be completed by November 1, 1992.
Appropriate corrective action will be taken if required by the outcome of this review.
1:DIR ADOCK- 05000361 p
Document Control Desk 2
If you have any questions regarding the enclosed report, please call me.
Sincerely, cc:
J. B. Martin, Regional Administrator, NRC Region V C. W. Caldwell, NRC Senior Resident Inspector, San Onofre Units 1, 2 & 3