ML13330B334
| ML13330B334 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 06/21/1988 |
| From: | Medford M SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| NUDOCS 8806230247 | |
| Download: ML13330B334 (7) | |
Text
Southern California Edison Company P. O. BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD. CALIFORNIA 91770 M.O.MEDFORD TELEPHONE MANAGER OF NUCLEAR ENGINEERING J
(818) 302-1749 AND LICENSING une 21, 9 88 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Gentlemen:
Subject:
Docket No. 50-206 Engineered Safety Features Single Failure Analysis San Onofre Nuclear Generating Station Unit 1 By letter dated April 5, 1988, SCE provided design descriptions of the modifications associated with the previously identified recirculation system single failure concerns. SCE committed in that letter to provide the final design description for the modification of recirculation valve MOV-358.
Accordingly, enclosure 1 to this letter discusses this modification.
Provided as enclosure 2 are revised pages to enclosure I to the November 20, 1987 submittal.
These revised pages clarify the design description of the integration of the third pump into the auxiliary feedwater system. The changes are indicated by bars in the right margin.
This submittal completes SCE's commitment to provide design descriptions for the modifications associated with the integration of third auxiliary feedwater pump, the steam/feedwater flow mismatch trip and the resolution of the single failure concerns identified in the October 16, 1987 submittal.
By Licensee Event Report (LER) No.87-015, Revision 1, dated May 17, 1988, SCE identified a single failure susceptibiliy of the containment spray system.
This susceptibility involves spurious closure of MOV-883 which would result in loss of the suction path from the refueling storage tank to the containment spray system. SCE has currently implemented measures to ensure the continued safe operation of the unit, as discussed in the revision 1 of the LER. In addition, SCE has initiated engineering design efforts to eliminate this single failure susceptibility and a design description of the associated modification will be provided by August 31, 1988.
If you have any questions or require additional information on this subject, please contact me.
Very truly yours, 8806230247 880621 DR ADOCK 05000206 P
CDCD cc:
J. B. Martin, Regional Administrator, NRC Region V K
F. R. Huey, NRC Senior Resident Inspector, San Onofre Units 1, 2 and 3
0 0
CYCLE X MODIFICATION DESIGN DESCRIPTIONS FOR RECIRCULATION VALVE MOV-358 SAN ONOFRE UNIT 1
Cycle X Modification Design Descriptions for Recirculation Valve MOV-358 San Onofre Unit 1 Introduction SCE previously committed to upgrade the auxiliary feedwater system (AFW) by automating and integrating the third AFW pump (installed to meet fire protection requirements during the Cycle IX refueling outage). Subsequently, SCE identified single failure susceptibilities of the Reactor Protection System (Steam/Feedwater Flow mismatch trip) and the Engineered Safety Features (main feedwater isolation and recirculation system).
Design descriptions for the integration of the third AFW pump, the steam/feedwater flow mismatch trip and main feedwater isolation were provided by letter dated November 20, 1987 and design descriptions for the recirculation system were provided in part by letter dated April 5, 1988. Modifications to correct the single failure susceptibilities of the recirculation valve MOV-358 are provided below.
Recirculation Valve MOV-358
- 1) Change power supply for recirculation isolation valve MOV-358 from MCC-3 to the Uninterruptible Power Supply (UPS) of Safety Injection Isolation Valve MOV-850C. (See attached Figure)
- 2) Provide new supply breaker for MOV-850C downstream of inverter output breaker and transfer switch to support maintenance activities or testing of the valves.
- 3) All work will be classified as Safety-Related, Seismic Category A.
The previously identified single failure susceptibity of the power supply to MOV-358 will be resolved by the post-Cycle X refueling outage addition of MOV-358 to the MOV-850C UPS. This modification will involve a change to the current UPS design basis and San Onofre Unit 1 technical specifications. The current UPS design basis was discussed in the safety analysis provided with License Amendment Application No. 116 submitted by letter dated November 30, 1983. The changes to the current design basis are discussed below. The appropriate technical specification change will be provided at a later date.
The safety function requirement of the MOV-850C UPS is to provide the necessary power for one operation of MOV-850C (stroking open and closed) during a Safety Injection event, coincident with a loss of offsite power and single failure of the train 2 diesel generator.
The UPS sizing calculation is currently based on a duty cycle of two consecutive operations of MOV-850C. In addition, the current sizing calculation utilizes the vendor's locked rotor current for the valve starting current. These assumptions were intended to be overly conservative.
-2 The revised (post-Cycle X) battery sizing calculation will be based on the following:
A) The duty cycle will be based on the most limiting sequence of events; Safety Injection Demand Loss of Offsite Power 11-sec Delay to Start Emergency Diesels Train 2 Diesel Fails to Start
- MOV-850C opens to permit safety injection into loop C
- MOV-358 opened at 30 minutes to permit recirculation
- MOV-850C closed The revised duty cycle is consistent with the current UPS safety function requirement discussed above.
B) The starting currents utilized for the revised UPS battery sizing calculation are based on MOVATS testing of the valves.
The usage of test data is considered appropriate since the MOVATS test values utilized take into account the maximum differential pressures expected on the valves during normal and abnormal conditions.
Additionally, the starting current values are used throughout the duration of each complete valve stroke, instead of the combination of starting and running values for each valve stroke. A value of 110% of the measured starting current is used in the sizing calculation to accommodate for a possible 10% overvoltage condition in the UPS. A temperature correction factor based on a 35 degrees F, instead of the nominal temperature of approximately 80 degrees F in the area was used in the calculation. A 25% design margin to compensate for battery aging is included. Finally, a design margin of 15% is also included in the calculation.
Based on the above discussion and the 37.5 kVA rating of the current inverter, the existing capacity of the MOV-850C UPS is sufficient to satisfy the new (Post-Cycle X) load requirements, resolve the previously identified single failure susceptibility of recirculation valve MOV-358 and meet the safety function requirements of MOV-850C and MOV-358.
REVISED PAGES TO ENCLOSURE 1 TO NOVEMBER 20, 1987 SUBMITTAL CYCLE X MODIFICATION DESIGN DESCRIPTIONS for AUXILIARY FEEDWATER SYSTEM UPGRADE STEAM/FEEDWATER FLOW MISMATCH TRIP MAIN FEEDWATER SYSTEM ISOLATION SAN ONOFRE UNIT 1
Cycle X Modification Design Descriptions for Auxiliary Feedwater System Upgrade Steam/Feedwater Flow Mismatch Trip Main Feedwater System Isolation San Onofre Unit I Introduction SCE previously committed to upgrade the auxiliary feedwater system (AFW) by automating and integrating the third AFW pump (installed to meet fire protection requirements during the Cycle IX refueling outage).
Subsequently, SCE identified single failure susceptibilities of the Reactor Protection System (Steam/Feedwater Flow mismatch trip) and the Engineered Safety Features (main feedwater isolation and recirculation). Accordingly, design descriptions for the integration of the third AFW pump, the steam/feedwater flow mismatch trip and main feedwater isolation are provided below. Modifications to correct the single failure susceptibilities of the recirculation system will be provided at a later date.
I. Auxiliary Feedwater System (AFW) Upgrades A) Add two new AFW flow control valves (FCVs) to the existing configuration so that two FCVs in parallel are provided on each AFW line. The parallel valves on each line will be on separate electrical trains.
Train F FCVs will fail closed on loss of control power and the Train G FCVs will fail open on loss of control power.
B) The control system for the new FCVs will be identical to that for existing FCVs.
C) Install a cavitating venturi downstream of the AFW flow control valve in each of the three AFW lines.
Each venturi will be sized so as to prevent Pump G1OS run-out and exceeding water hammer flow restrictions to depressurized steam generators. Two normally closed bypass valves, in series, will be provided for each venturi to accommodate greater flow rates should such operation be deemed desirable and safe.
D) A cavitating venturi is to be placed in the discharge of the GlOW pump so as to prevent exceeding the maximum flow limit to each steam generator under any sequence of events independent of the number of steam generators available. Two normally closed manual bypass valves, in series, shall be provided for the venturi to accommodate Dedicated Safe Shutdown operation of GlOW.
E) Realign GlO to the same electrical train as GlOS (i.e., Train F).
F) Add GlOW to electrical Train G.
-2 G) Revise the existing control room panel to include the same controls, indication and alarms for GlOW as exist for the other motor driven AFW pump. The control room panel will be revised in accordance with human factors guidelines as established by the Control Room Design Review. This will include:
- 1. Suction and discharge pressure indication, and low suction pressure pump trip and alarm.
- 2. Control switches and position indication of GlOW discharge valve, CV-3110.
- 3. Pump manual Start/Stop switches with running lights and ammeter.
H) Remove the GlOS low discharge pressure trips, but retain the indication and alarm functions of the instrumentation. Pump runout protection will be provided by the venturi in each of the three AFW discharge lines.
I) Provide a manual transfer switch for selecting Dedicated Safe Shutdown (DSD) or normal Safety Related power for GlOW locally.
This switch will provide isolation between the normal and DSD power supplies.
- 3) Modify the auto-mode control circuit of each pump and respective discharge valve to operate as follows upon receipt of the steam generator low level signal (AFWS auto initiation).
- 1. Lead Train G Pump (GlOW) will immediately start and provide flow, turbine driven Train F pump (GlO) will begin "warm-up mode" (steam bypass valves and drain valves open and turbine running at 2000 RPM).
- 2. After a given time delay, to.allow the Train G to respond, lag Train F pumps (GlOS and G10) will begin to provide flow upon a no flow signal from the GlOW pump discharge manifold.
- 3. Train F pumps (GlOS and G10), if operating, will stop providing flow upon a flow signal from the Train G pump (GlOW) discharge manifold. (GlOS will trip, G10 will return to "warm-up mode" and pump discharge valves close.)
- 4. Separate Train F flow switches will be provided on the GlOW pump discharge manifold for control of the Train F pumps and control of the Train F pump discharge valves to prevent postulated single failures from causing inadvertent operation of both trains.
K) An interlock will be provided between each AFW pump and its respective discharge valve, so that pump discharge pressure will be required in order for the discharge valve to open in automatic mode.
L) Provide instrument air and back-up nitrogen for the Train G pump (GlOW) discharge valve CV-3110.
M) All work will be classified as Safety-Related, Seismic Category A.
(See Figure 1.)