ML19260B517

Proposed Automatic Initiation Scheme for Auxiliary Feedwater Sys

ML19260B517
Person / Time
Site:	Haddam Neck, Millstone  File:Connecticut Yankee Atomic Power Co icon.png
Issue date:	12/31/1979
From:	NORTHEAST UTILITIES
To:
Shared Package
ML19260B512	List: ML19260B511 ML19260B517
References
TASK-10, TASK-RR TAC-42410, TAC-44705, TAC-44746, NUDOCS 7912100294
Download: ML19260B517 (7)

Text

DOCKET NO. 50-336 ATTACHMENT 2 MILLSTONE NUCLEAR F0WER STATION, UNIT NO. 2 PROPOSED AUIDMATIC INITIATION SCHEME FOR AUXILIARY FEEDWATER SYSTDIS DECDIBER, 1979 1521 324

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Introduction The AFW system at MP-2 consists of two half capacity motor driven AFW pumps and one full capacity turbine driven pump. Each motor driven pump is powered from a separate and redundant emergency bus. The turbine is supplied with steam from either main steam header. Each AFW turbine steam supply header isolation valve is normally open. The combined header steam admission valve is normally closed.

The auxiliary feedwater valves will be lef t in their operating position so that only the check valves have to change position to commence feeding.

The AFW feed regulating valves will be prepositioned to provide 300 GPM flow to each SG at normal isolated SG pressure. The pump discharge crossconnect valve will be normally open. This allows feeding either steam generator with, two motor driven AFW pumps or with the turbine driven AFW pump. The pump suction crossconnect valve will be normally closed thus the turbine driven pump will receive water from the condensate storage tank from one suction line while the motor driven pumps will receive water from the condensate storage tank from another suction line. The attached diagram is provided to illustrate the above description.

AFW Initiation Steam generator level will be the only parameter sensed to initiate AFW automatically. The system will consist of two trains, Facility Z1 and Facility Z2.

For each train two level signals from each steam generator will be applied to bistables. The dry contact outputs of the bistables will be m.trixed to two out of four. The matrix will control two lockout relays per train. Two control selector switches between the bistables and the lockout relays will be used to pass or block the auto start signal, trip the lockout relays, or reset the lockout relays. One switch will be located on the control room panel i521 325

(C05) the other on the hot shutdown control panel (C21). The block is accomplished by moving either switch to a " pull or lock" position. The pull to lock operation requires an extra step from normal switch operation, and once accomplished the switch is in a visually abnormal position, making it distinct from other switches on the control board, The block position will also be annunciated in the control room and an amber light will be lit at panel C21.

One lockout relay per train supplies a contact to start a motor driven AFW pump. The start signal to the mo tor driven pump will be blocked if the emergency diesel generator is required to start and sequentially accept loads from its emergency bus.

In this mode (and with SO level low) the AFW pump will be sequenced onto the diesel in load group four, twenty seconds after sequencing commences. Another contact from the first lockout relay causes an alarm in the control room and lights a red light at C05 and C21 indicating pickup of the lockout relay and automatic AFW system initiation. The second lockout relay in the train provides a contact to the circuit for the motor operated AFW regulating valve associated with the train, and a contact to open the combined steam admission valve for the turbine driven AFW pump. The open signal to the AFW regulating valve will be interrupted by a valve position limit switch.

The AFW regulating valve will be prepositioned as mentioned before and the open signal is provided to guarantee that a flow path is available.

One lockout relay in each train starts its respective motor driven AFW pump.

A second lockout relay in each train provides start signals to the turbine and guarantees a flow path for its respective train.

1521 326 NUREG 0578 Design Requirements 1.

The design provides for the automatic initiation of the auxiliary feedwater system by sensing a low steam generator level, starting the three AFW pu=ps and assuring an adequate flow path.

2.

The signals and circuits have been designed so that a single failure will not result in the loss of auxiliary feedwater system function. The signals and circuits will be arranged in trains.

Separation of signals and circuits will be maintained in accordance with established plant separation criteria for safeguard systems. Two level signals from each steam generator will be used per train. The level signals will be grouped according to their power source either Z1 or 22.

Two separate two out of four matrices will be extablished to operate four relays (twc per train). The loss of one complete power train would still provide a minimum of one AFW flow path and one motor driven pump. The turbine driven pump would not star' automatically if pcwer for the steam admission valve was aligned to the unavailable power facility. The operator has turbine RPM, inlet steam pressure, and steam admission valve position indicating lights displayed on control room panel C05. For the assumed case where the turbine driven pump has failed to start because power to the selected emergency bus has been lost, turbine speed and inlet steam pressure would be zero, indicating the turbine driven pump has failed to start.

Both the open and the closed indicating lights for the steam admission valve would be out indicating a loss of power to the valve control circuit, thus indicating the cause for the failure of the turbine driven pump to start. The operator would have ample time to proceed to the Hot Shutdown 1521 327

Control Panel (C21), about fif ty feet away, and select the known available power source. This will be identified because one of the motor driven pumps will have started, and be providing fifty percent of the required auxiliary feedwater flow. Loss of one complete power train would still permit responding to a low steam generator level in either steam generator as two level detectors for each steam generator would still be operable and powered from the redundant train.

3.

Testability of the level signals will be included in the design engineering of the proposed change. The entire system can be tested by inserting signals in the level current loops. This method may also be employed in testing one current loop and associated histable at a time. The lockout relays and actuated equipment can be tested by placing either of the switches between the bistables and the relays in the start position. The entire system can be tested as a whole or the signal portion and the relay and actuated equipment portion can be tested separately.

4.

The initiating signals and circuits are powered from the emergency buses, from the vital buses via the inverters, or from the battery buses.

Power to operate the combined steam admission valve to the turbine driven AFW pu=p may come from a Z1 motor control center or a 22 motor control center.

Cable separation will be verified before upgrading its classification from facility 5 to facility Z5.

5.

Manual capability to initiate the auxiliary feedwater system from the control room will be retained. The AFW system may be started either by operating individual switches for each component or by going to the start position with the two new switches on C05. A single failure in the manual circuit will affect only one of the two redundant trains.

1521 328 6.

The AC motor dri - 7 umps and valves in the auxiliary feedwater system have been included in the automatic actuation of the loads to the emergency buses. The valves receive open signals regardless of the emergency bus conditions since the motors involved are less than two horsepower total.

The motor driven pumps are sequenced onto the emergency bus as previously discussed.

7.

The automatic initiating signals and circuits have been designed so that their falure will not result in the loss of manual capability to initiate the AFW system from the control room. The automatic signals and circuits have been designed to supplement but not interrupt the manual control of the AFW system. Failure by short circuit could start one train but would not affect the other train. Failure by open circuit would still permit normal manual control.

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