ML19295D182
Text
.,
..s GU.ATORY 00CKET ME COPY
~ "
m..
.O.Af MEMORA':DUM FOR:
Robert L. Tedesco, Assistant Director for Licensing Division of Licensing FRCM:
Paul S. Check, Assistant Cirector for Plant Systems Division of Systems Integration
SUBJECT:
FARLEY UNIT 2 - TRAIN SEPARATICN OF THE POWER SUPPLY TO THE AFW FLOW CONTROL SOLE l;0ID VALVES Sy memorandum dated July 25, 1980, the Instrumentation and Control Systens Branch (ICSS) provided its evaluation of the Farley (fnit 2 auxiliary feedwater system (AFWS) automatic initiation and flow indication systems.
At that time, the automatic initiation logic, instrumentation, and circuitry was found to be acceptable with the following exception. All six air (solenoid) operated ficw control valves in the AFUS flow lines were found to be pcwered from the same train A battery / charger. This design was found to be susceptible to single failures (e.g., overvoltage conditions) which could preclude these valves from performing their required safety function and thus negate auxiliary feedwater ficw to the steam generators.
By letter dated September 8,1980, the applicant (alabama Power Company) submitted propcsed desien modifications to prevent single failures from pre-cluding operation of the AFWS ficw control valves. This design change consists of the addition of one train 8 powered solenoid vent valve in the air line to each of the AFWS ficw control valves.
Based on our review, we conclude that the above modification resolves our concern regarding the pcwer source to the AFWS ficw control valves.
The automatic initiation system for the Farley Unit 2 AFWS meets the staff's long term safety grade requirements and, therefore, is acceptable.
Out Safety Evaluation is enclosed.
m.,,,
Vaal s. chee:s Paul S. Check, Assistant Director for P1 ant Systems Division of Systems Integration
Enclosure:
As stated cc:
D. Ross D. Thatcher DISTRIBUTION:#g R. Satterfield R. Kendall Cccket File %
- 0. Parr*
ICSB Reading File M. Srinivasan PCheck Can ta c t:
L. Kintner R. Kendall
- 3. J. Youngblcod E9430 J. T. Seard W. LeFave
--> -.. tr u ICSB ISCB-l.~ICSB j
~
i 1.
..I
.J
-_...-_-W e
h *
$h ad E
6 k
. ' ' + "
D
SAFETY EVALUATION FARLEY UNIT 2 TRAIN SEPARATION OF THE POWER SUPPLY TO THE AUXILIARY FEEDWATER FLOW CONTROL VALVES I.
INTRODUCTION During the ICSB review of the Farley Unit 2 Auxiliary (Emergency) Feedwater System (AFWS) automatic initiation and flow indication circuitry (Action Plan Item II.E.1.2), it was discovered that all six air (solenoid) operated flow control. valves (FCV) in the AFWS flow lines were powered from the same train A battery / charger. During normal operation, the redundant flow control valves (two to each steam generator) would be kept closed by keeping the solenoid valves in the FCV air lines continuousl energized. Upon an auxiliary feedwater initiation signal, the power to the solt.noids would be interrupted causing them to provide a vent path for the air to the FCVs and thus allowing them to open.
This design was found to be unacceptable as all six control valves were susceptible to comon power source perturbations (e.g., overvoltage conditions) which could preclude these valves from performing their required safety function and thus negate auxiliary feedwater ficw to the steam generators. The staff concluded that this design was in violation of the single failure criterion of GDC 44. The applicant (Alabama Power Company) was required to provide train separation of the power supplies for the solenoid valves or to show the design to be acceptable on some other basis.
By letter dated September 8,1980, Alabama Power Company proposed design modifications to provide train separation of the power supplies for the AFWS flow control valves.
2-II.
EVALUATION The proposed design change consists of adding one solenoid valve (SV-C),
powered from a train 8 supply, to the air line of each FCV.
placement of either SV-A (A-train) or SV-C (B-train) in the vent position (de-energized) will remove air from the valve and cause it to move to the full open position.
Initiation of a train A or train B emergency signal will cause the valves to move to the full open position. Failure of either the train A solenoid valves (SV-A) or the redundant train B (SV-C) solenoid valves will not prevent the FCVs from being placed in the full open position, whether initiated oy automatic signal or operator action.
During normal operation (above 5% power) the AFWS flow co'ntrol valves are kept closed. During plant startup or normal cooldown, the valves are placed in the modulate mode and the controller in the air supply line is used to position the valves to obtain the desired flow rate.
Initiation of an emergency signal will result in the FCVs moving to the full open position regardless of the controller mode (open, close, or modulate) at the time of the emergency signal initiation.
III. CONCLUSION Based on our review of the applicant's submittal, we conclude that the modifications to the AFWS flow control valve power supply arrangement alleviates our previous concern and that the AFWS automatic initiation system meets the staff's long term saft-ty grade requirements, and therefore, is acceptable.