ML13310B055

Safety Evaluation Concluding That Proposed Change 98 Re Auxiliary Salt Water Cooling Pump Unacceptable.Deficiencies Identified.Alternatives Presented

ML13310B055
Person / Time
Site:	San Onofre
Issue date:	10/28/1983
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML13310B053	List: ML13310B052 ML13310B055
References
TAC-65149, NUDOCS 8311010394
Download: ML13310B055 (4)

Text

0 UNITED STATES NUCLEAR REGULATORY COMMISSION O

WASHINGTON, D. C. 20555 SAFETY EVALUATION SAN ONOFRE NUCLEAR GENERATING STATION, (SONGS) UNIT 1 AUXILIARY SALT WATER COOLING PUMP DOCKET NO. 50-206

1. INTRODUCTION By letter dated August 27, 1980 (Proposed Change No. 98) Southern California Edison Company requested a revision to Technical Specifi cation Section 3.3.1.

The change would eliminate consideration of the non-seismically qualified auxiliary salt water cooling (ASWC) pump in determining the operability of the salt water cooling system.

Only the North and South salt water cooling (SWC) pumps, which are seismically qualified would be considered when establishing the operability of the salt water cooling system. The change request is based on Region V letter to the licensee dated April 4, 1980. By reference 2, the staff suggested immediate implementation of the subject changes until appropriate modifications are made to the ASWC pump and appropriate changes are made to SONGS, Unit 1 technical specifications. The intent of these changes is to inbrease the reli ability of the salt water cooling system by eli6Iinating reliance on a non-qualified component.

2.0 EVALUATION The existing technical specification requires that the reactor not be made or maintained critical unless two SWC pumps (North and South) or one SWC pump (North or South) and the ASWC pump are operable.

By eliminating the option of including ASWC pump in the salt water cooling system and not placing it as a backup or standby unit, the RHR cooling system will depend only on the two SWC pumps which have the following design characteristics which have shown the system to be less reliable than desired.

(1) Both pumps are located in a common pit (circulating water pump (CWP) pit) and, thus, are subjected to common mode failure by flooding.

On May 13, 1982 both pumps were made inoperable due to flooding.

(2) During normal operation either one of the two pumps is capable of performing its function. However, if a cooldown is required in case of a tube rupture or some other accident, one pump is not sufficient to provide adequate cooling. Additionally, when the RHR system is first placed in service during plant shutdown, both component cool ing water heat exchangers and hence both the salt water cooling pumps are relied upon (Reference 4).

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-2 (3) The reliability of the SWC system has been poor with 4 system failures within 3 years.

The licensee is reviewing the SWC system for the single failure criterion under SEP Topic IX-3. References 4 and 5 have considered the ASWC pump as a back up to the SWC pumps. The ASWC pump can be used as back-up if the SWC pumps are inoperable or insufficient as previously indicated. The ASWC pump is suitable for the back-up function for the following reasons.

(1) It is located in a separate pit, remote from CWP pit.

(2) Its motor is supplied from a safety related 480 volt load center and, as such is electrically as qualified as the SWC pumps.

(3) Its capacity is the same as that of a SWC pump (4600 gpm).

(4) The licensee intends to enhance the pumps reliability and dependability by improving the vacuum priming system, installing mechanical seals to minimize air inleakage or provision for gland sealing water (Reference 3).

(5) The pump is different in design (a horizontal rather than vertical pump) and therefore adds diversity to the salt water cooling system.

The ASWC pump does not have seismic qualificatioR but does contribute significantly to the overall system reliability. In addition, the SWC screen wash pumps were used as back-up pumps during some of the SWC sytem failures.

The technical specification should therefore address both the ASWC pump and the screen wash pumps as a back up sources of cooling, in addition to the two SWC pumps, to be available during periods when the plant is in Modes 1, 2, 3, and 4.

We believe that during the short period of time when one of the SWC pump is inoperable, if the ASWC and screen wash pumps are available as back-up pumps, there is an acceptable low probability of an earthquake which could cause ASWC pump to be inoperable, and a single failure which would make the second SWC pump inoperable.

CONCLUSION Based on the above evaluation, we conclude that the proposed changes to the technical specifications, are unacceptable. Our evaluation identifies the

-3 deficiencies in the proposed changes and presents alternative changes that would be acceptable.

4.0 ACKNOWLEDGEMENT G. Holahan prepared this evaluation.

Dated:

October 28, 1983

-3 References

1. Southern California Edison Co. letter (R. Dietch) to NRC (H. Denton) dated August 27, 1980.

2. NRC (Region V) letter (R. Engelken) to Southern Californta Edison Co.

(L.T. Papay) dated April 4, 1980.

3. Southern California Edison Co. letter (L.T. Papay) to NRC CR. Engelken, Region V) dated May 12, 1981.

4. AEOD memo (C. Michelson) to NRR (H. Denton) dated March 4, 1982.

5. NRC letter (D. Crutchfield) to Southern California Edtson Co. (R. Dietch) dated March 18, 1981.