ML20206D713
| ML20206D713 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 04/27/1999 |
| From: | Scherer A SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9905040217 | |
| Download: ML20206D713 (3) | |
Text
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' $OUTiffRN Calif 0RNIA A. Edward Scherer i
SS EDISON ttX; b m
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April 27,1999 U.S.- Nuclear Regulatory Commission Document Control Desk Washington, D. C. 20555 Gentlemen:
Subject:
Docket Nos. 50-361 and 50-362 Comments on Preliminary Accident Sequence Precursor Analysis of Linestarter Failure San Onofre Nuclear Generating Station, Units 2 and 3
References:
- 1) Letter from James W. Clifford (USNRC) to Mr. Harold B. Ray, 1
Subject:
Review of Preliminary Accident Sequence Precursor Analysis of Operational Condition at San Onofre Nuclear Generating j
Station, Unit 2, dated March 23,1999.
y
Subject:
Docket Numbers 50-361 and 50-362, Linestarter and AFW Supplemental Information, San Onofre Nuclear Generating Station, Units 2 and 3, dated April 7,1998.
Reference 1 transmitted a preliminary Accident Sequence Precursor (ASP) analysis associated with the February 1998 failure of the containment sump isolation valve linestarter for our review. Southern California Edison (SCE) has reviewed the analysis and would like to provide information that may not have been readily available to the contractor at Oak Ridge National Laboratory who prepared the analysis. We believe
' incorporation of this information will allow the ASP analysis to be more realistic. SCE appreciates that the ASP analysis includes the recovery actions included in the SCE analysis (provided in Reference 2) and view this as a positive step by the NRC to provide a realistic analysis. The attachment to this letter provides SCE's comments, if you have any questions please contact me.
Sincerely, 9905040217 7
e 990427wj em L Attachment f
cc:
E. W. Merschoff, Regional Administrator, NRC Region IV g
J. A. Sloan, NRC Senior Resident inspector, San Onofre Units 2 and 3 g
L. Raghavan, NRC Project Manager, San Onofre Units 2 and 3
).k i
P. O. Box 128 San Clemente. CA 92674-0128 949-368-7501 Fax 949 368-7515
Attrchmsnt SCE COMMENTS ON ACCIDENT SEQUENCE PRECURSOR ANALYSIS OF LINESTARTER EVENT (Page 1 of 2)
Southern California Edison (SCE) has reviewed the Accident Sequence Precursor (ASP) analysis provided in Reference A. The analysis is consistent with information provided in LER 2-1998-003-01 (Reference B) and the April 7,1998, SCE letter (Reference C). In two instances information which was not specifically included in References B and C, but considered in the SCE probabilistic risk assessment (PRA),
should be considered in any revision to the ASP analysis. In addition, SCE has comments on the Additional Event-Related Information section of the analysis which should be considered for incorporation.
Modelina Assumotions and Analysis 1)
For Case 1 of the ASP analysis, the common cause failure probability of " Sump Isolation Motor-Operated Valves" failing to open was increased from 1.1 E-003 to 8.8 E-002 based on the potential of the other sump isolation valves to also fail due to grit. In response to NRC Inspection Report 98-05 (Reference D), SCE provided additional information relative to the estimated number of valve actuations (17,000) in the presence of the grit with only the one failure. Based on this plant specific data, there was no evidence that the potential for common cause failure was impacted by the grit. Therefore, SCE believes the increase in common cause probability is not appropriate.
2)
Case 3 of the ASP analysis models the unavailability of the Refueling Water
-Storage Tank (RWST) Train B outlet valve as a failure of that valve in the closed position thus preventing Train B inpction. The RWST Train B outlet valve unavailability included in the LER was for breaker indicating light replacement.
During this maintenant e, the valv9 was open and available to allow injection.
Therefore, from a PRA perspctWe, the 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> and 45 minutes stated in the LER is not risk significant. This conclusion was included in Inspection Report 98-05, Reference E.
Additional Event-Related Information Section The first paragraph infers that the linestarter replacement had just begun in February of 1998. The linestarter replacement began in 1995 after the linestarter failure due to excessive wear of the sliding cams. The linestarter replacement was completed in 1998. It is~ suggested that the "just started" in the first sentence be replaced with "been" to reflect the correct tirmog.
The second paragraph includes information from the LER (Reference B) which indicated that the source of the grit was most likely gunite similar to what was used for hi!! side stabilization. In the response to NRC Inspection Report 98-05 (Reference D), additional information was provided that indicated the grit substance had the same elemental, visual and size characteristics as unmixed Portland cement. Reference D, further indicates that the deposition of the grit took place during construction activities and that
a Attachment
(
SCE COMMENTS ON ACCIDENT SEQUENCE PRECURSOR ANALYSIS OF LINESTARTER EVENT (Page 2 of 2)
I potential sources included batch plant operation, grouting and guniting activities. It is suggested that the reference to gunite used to stabilize the hillsides in the first sentence of the second paragraph be deleted and replaced with "... identified as Portland cament particles...." In addition it is suggested that the response to NRC Inspection Report 98-05 be referenced at the end of the second paragraph and added to the References section.
References
.A)
Letter from James W. Clifford (USNRC) to Mr. Harold B. Ray (SCE),
Subject:
Review of Preliminary Accident Sequence Precursor Analysis of Operational Condition at San Onofre Nuclear Generating Station, Unit 2, dated March 23,1999.
B)
Letter from R. W. Krieger (SCE) to Document Control Desk (USNRC),
Subject:
Docket No. 50-361, Revised 30-Day Reports, Licensee Event Report Nos.1998-001-01 and 1998-003-01, San Onofre Nuclear Generating Station, Unit 2, dated April 17,1998.
C)
Letter from Dwight E. Nunn (SCE) to Document Control Desk (USNRC),
Subject:
Docket Numbers 50-361 and 50-362, Linestarter and AFW Supplemental Information, San Onofre Nuclear Generating Station, Units 2 and 3, dated April 7, 1998.
D)
Letter from Dwight E. Nunn (SCE) to Document Control Desk (USNRC),
Subject:
Docket Numbers 50-361 and 50-362, Response to inspection Report 98-05 Regarding Linestarters, San Onofre Nuclear Generating Station, Units 2 and 3, dated June 22,1998.
E)
Thomas P. Gwynn (USNRC) to Harold B. Ray (SC Q,
Subject:
NRC Special Inspection Report 50-361/98-05; 50-362/98-05, dated May 21,1998.