ML18106A370

Provides Specific Info Requested by NRC & Overall Response Re Corrections to SER for Amend 69 to Unit 2 Ts.Info Re Mitigation of LOCA in Mode 4 Encl

ML18106A370
Person / Time
Site:	Salem
Issue date:	03/06/1998
From:	Dawn Powell Public Service Enterprise Group
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LR-N980091, NUDOCS 9803180380
Download: ML18106A370 (4)

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Public Service Electric and Gas Company P.O. Box 236 Hancocks Bridge, New Jersey 08038-0236 Nuclear Business Unit MAR 0 6 1998 LR-N980091 United States Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 ADDITIONAL INFORMATION FOR CORRECTIONS TO AMENDMENT 69 SAFETY EVALUATION REPORT SALEM GENERATING STATION UNIT NO. 2 DOCKET NO. 50-311 - *,

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Ladies and Gentlemen:

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On May 27, 1997, Public Service Electric and Gas (PSE&G) submitted letter LR-N970293 for corrections to the Safety Evaluation Report for Amendment 69 to the Salem Unit 2 Technical Specifications. As a result of this letter, the NRC requested, during a I

conference call, that PSE&G provide additional information regarding the mitigation of a Loss of Coolant Accident (LOCA) in Mode 4. The specific information requested by the NRC and PSE&G's overall response are provided below:

NRC Questions:

• Why is the Refueling Water Storage Tank (RWST}'-draindown times during a Mode 4 LOCA longer than the Mode 1-3 LOCA?

• In general, what does the procedure entail for mitigation of the Mode 4 LOCA?

• What would the draindown time in Mode 4 (past and present) be for Unit 2?

PSE&G Response:

In a letter qated January 5, 1987, PSE&G responded to an NRC request for additional information regarding the mitigation of a Mode 4 LOCA. In the letter, PSE&G indicated that if a LOCA were to occur during MODE 4 operation, with the semi-automatic switchover system disarmed, the operator would initiate manual actions consistent with _-\/

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the procedures in plac~, t~ shift each train over to the c~ntainment sump. f'>-<_07.Ji D

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0 Document Control Desk 2 LR-N980091 MAR 0 6 1998 The draindown time of the RWST from the low level alarm to the unusable water level with the assumption that the operator fails to stop a containment spray pump for conservatism was calculated to be approximately 18.5 minutes.

This time of 18.5 minutes was based on an available RWST volume of 129,300 gallons and a total pump flow of approximately 7000 gallons. The 7000 gpm included an assumed maximum flow rate of 5200 gpm for two (2) Containment Spray (CS) pumps. The current analysis uses a maximum flow rate of approximately 7200 gpm (depending on Containment pressure conditions) for two (2) CS pumps. This CS pump flow rate is a major factor in the current RWST draindown rates.

Recent RWST draindown evaluations have resulted in revised draindown times. The limiting draindown time for a Unit 2 LOCA in Modes 1-3 is 11.2 minutes. The RWST draindown times for a LOCA in Mode 4 is conservatively estimated to be in excess of 18 minutes. The reason for the increased time is described below.

The Mode 4 LOCA procedure, S2.0P-AB.LOCA-0001(Q) "Shutdown LOCA", is different than the Mode 1-3 LOCA procedures EOP-LOCA-1 through 5. A major difference is that for Mode 4 LOCA mitigation, the operators must prevent the potential for overpressurization of the Reactor Coolant System (RCS). The Mode 4 LOCA procedure requires that a single train be aligned and pumps started in a controlled, conservative manner so as to not create an overpressure condition.

The Shutdown LOCA procedure is applicable for a LOCA that occurs after isolation of the accumulators, in the lower end of Mode 3, or in Mode 4. In the Shutdown LOCA procedure, the minimum number of pumps would be started to provide sufficient core cooling but not overpressurize the RCS. Since the number of pumps operating is controlled by the procedure (to avoid possible overpressure situations), the drawdown rate on the RWST is reduced. This reduced drawdown rate significantly extends the draindown time of the RWST beyond the limiting MODE 1-3 analysis time of 11.2 minutes.

In a Mode 4 LOCA scenario, when the RWST low level alarm is received, transfer to cold leg recirculation (single train) is manually initiated. The transfer procedure is*

contained in Attachment 2 of the AB LOCA procedure and is similar for both Units.

Dqcument Control Desk 3 IMAR 06 1998 LR-N980091 In order to conservatively bound the MODE 4 LOCA draindown time, one Safety Injection (SI) pump and one Charging/SI (C/SI) pump is assumed to continue to take suction from the RWST and inject into the core during the entire transfer to cold leg recirculation. Additionally, one Residual Heat Removal (RHR) pump is assumed to be transferred to the containment sump within 4 minutes of the receipt of the RWST low level alarm and one CS pump continues to draw from the RWST until the CS pump is stopped at the RWST low-low level alarm.

Based on the conservative assumptions above, the minimum time available for switchover to cold leg recirculation to occur (from the RWST low level alarm setpoint to the RWST low-low level alarm setpoint) is greater than 19 minutes.

Salem Unit 2 Past (Amendment 69) Current RWST Draindown MODE4 LOCA MODE4 LOCA Available RWST Volume =129 300 gal. Available RWST Volume =108 500 aal.

Recirculation Mode ~18.5 minutes ~19.1 minutes If you have any questions concerning the above information, please do not hesitate to contact us.

Sincerely, j),£.4 D.R. Powell Director - Licensing/Regulation and Fuels

Document Control Desk 4 LR-N980091 MAR 0 6 1998 C Mr. Hubert J. Miller, Administrator - Region I U. S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406 Mr. P. Milano, Licensing Project Manager- Salem U.S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 14E21 Rockville, MD 20852 Ms. M. Evans (X24)

USNRC Senior Resident Inspector - Salem Mr. K. Tosch, Manager, IV Bureau of Nuclear Engineering P.O. Box415 Trenton, NJ 08625