ML20041D339

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Midland Auxiliary Feedwater Reanalysis.
ML20041D339
Person / Time
Site: Midland
Issue date: 02/25/1982
From:
PLG, INC. (FORMERLY PICKARD, LOWE & GARRICK, INC.)
To:
Shared Package
ML20041D330 List:
References
RTR-NUREG-0611, RTR-NUREG-611 NUDOCS 8203050242
Download: ML20041D339 (9)
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Pickard, Lowa and Garrick, Inc. Enclosuro 2 to I February 25, 1982 serial 16008 l MIDLAND AFW RELIABILITY REANALYSIS This report discusses and presents the results of studies performed to determine the reliability of the auxiliary feedwater system (AFWS) for Midland Units 1 and 2. The analyses presented here are based upon discussions with the Nuclear Regulat9py Comission (NRC) concerning the AFW analysisitpresented discussions, in NUREG-0611W. was determined As a result that the reliability of theg analysis performed on the Midland AFWS differed in the following respects from the analyses performed in NUREG-0611:

1. NUREG-0611 looked at all combinations of bus failure with a concurrent loss of diesel generator offsite failure power and obtained fromthen assignedSafety the Reactor the frequenc{3jf Study to the bus that produced the largest change in system frequency of failure. The Midland AFW reliability analyses treated both diesel generators probabilistically.
2. Human action to recover from AFWS failure were included in the NUREG-0611 analyses. These actions included shifting of water supplies outside the control room within 20 minutes, and other actions which the operator could reasonably be expected to take during the transient of interest. The Midland reliability analysis did not include operator recovery actions after system demand except for closing a full flow test valve for a pump under test.

Because of these concerns, a reevaluation of the Midland AFWS was perfonned to allow a more accurate comparison to the NUREG-0611 AFW analyses 

                < 1 x 10 gnd forthe stated a loss      safetypower cf offsite   goal for system induced   lossunreliability of of main feedwater transient.

This reanalysis assigns the probability of diesel generator failure from . the Reactor Safety Study (RSS) to Class 1E bus 1A05 (2A05) which is the normal feed for the motor-driven AFW pump. Electric power is assumed to be available at Class 1E bus 1A06 (2A06). Three possible human recovery actions are considered in these AFWS analyses.

1. Starting of the motor-driven AFW pump on the opposite Class IE bus in the event of diesel generator failure to start.
2. Recovery of pump train failures during testing of the AFW pumps.
3. Recovery from the identified common cause failure of the AFW pump trains.

Experience from operating plants indicates that approximately 50*. of the turbine-driven pump failures to start on demand are recoverable by operator action within a short period of time after occurrence. However, because of the limited once through steam generator (OTSG) water , inventory, no credit is taken for these recovery actions. Experience  ; from operating Babcock and Wilcox (B&W) plants also indicates that l sufficient steam inventory may be available in a " dry" 0TSG to allow I l 8203050242 820301 PDR ADOCK 05000329 A PDR 1 0176C022582

turbine-driven AFW pump start or restart at times greater than 5 minutes after the loss of OTSG water inventory. A review of Nuclear Power Experience (NPE)(4) was conducted to determine the number of AFW malfunctions that occurred during actual AFW demands. The data in NPE discusses events reported from 1970 to 1981. Of approximately 50 events describing AFW malfunctions during system , demand, no complete and sustained AFW system failures are reported. Of the eight complete losses reported, operator action to restore feedwater flow was successful within a time of 10 minutes. These times include operator actions inside and outside the control room. The times allowed for the human recovery actions considered in this analysis are: 0 to 5 minutes; 5 to 10 minutes; 10 to 15 minutes; 15 to 20 minutes; and greater than 20 minutes. The results for each of these time periods are presented separately and different frequencies of operator error are assigned to each allowed recovery action and time period analyzed. These values are based upon the recommended values presented in NUREG-0611. An operator recovery scenario was developed for each recovery action. These scenarios are:

1. Start of the motor-driven AFW pump on the opposite Class 1E bus after failure of the emergency diesel generator (EDG) supplying the nomal 1E bus.
a. Indications of Failure (1) Loss of offsite power - turbine trip, reactor trip, loss of main feedwater, loss of nonvital bus voltage, frequency and load indication.

(2) Loss of EDG supplying 1A05 (2A05) - EDG trip alarms, no - voltage, frequency or load indication on bus 1A05 (2A05). (3) AFWS failure - turbine-driven AFW pu ap trip alarms, no (low) AFW flow or discharge pressure, decreasing OTSG 1evels and associated alarms, increasing reactor coolant system (RCS) temperature and pressure. Using the guidance provided by NUREG-0611, one EDG (supplying bus 1A05 (2A05) is assumed to fail with a frequency of 3.7 x 10-2' based upon electric power analysis performed in the reactor safety study for a typical pressurized water reactor (PWR). The other EDG and associated Class 1E bus are assumed to be available with a probability of 1.0.

b. Operator Actions to Start the Motor-Driven AFW Pump on Bus 1A06 (2A06)

(1) Send an auxiliary operator to the Class 1E switchgear rooms , to start the motor-driven AFW pump. A sufficient number of l auxiliary operators will be on shift at all times for Midland. l 2 l 0176C022582 

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(2) The auxiliary operator proceeds to the "A" switchgear room.  ; (3) The auxiliary operator racks the AFW pump breaker to disconnect and removes the kirk key from the breaker. (4) The auxiliary operator proceeds to the B switchgear room, inserts the kirk key for the breaker, racks the breaker to the operate position, and starts the motor-driven AFW pump. (5) The auxiliary operator notifies the operators in the control room. This step is not vital as AFW pump flow, pressure, and operating amperes are available in the control room.

c. The Frequency of Operator Error for the Time Periods Considered Are:

(1) 0 to 5 minutes - because of the short tine available for operator recovery, no recovery of the motor-driven AFW pump due to loss of the EDG supplying 1A05 (2A05) was considered. (2) 5 to 10 minutes - the frequency of operator error assigned is 0.5. This time period allows added time for operator recognition of tne problem and getting the auxiliary operator to the switchgear room for recovery. (3) 10 to 15 minutes - the frequency of operator error is assigned 0.1. (4) 15 to 20 minutes - the frequency of operator error is assigned 0.05. (5) 20 minutes and longer - the frequency of operator error assigned is 0.005. These frequencies of error are based upon the recommendations contained in NUREG-0611.

d. All Operator Frequencies of Error Are Based Upon the Following Assumptions (1) The plant procedures for loss of main feedwater present the indications available to the operator for determining a loss of auxiliary feedwater flow.

(2) The loss of main feedwater procedures includes the recovery options available to the operator for a loss of auxiliary feedwater flow. (3) The operators are trained to recognize the symptoms of a loss of auxiliary feedwater flow and the cause of the loss of flow. 0176C022582 'l

(4) Operator training has been carried out on the procedures for starting the motor-driven AFW pump on the opposite Class 1E bus. (5) The operator priorities for a loss of main feedwater flow are: (a) Recover auxiliary feedwater flow. (b) Control RCS temperature using feed and bleed methods. (c) Recover power to the Class 1E buses.

2. Recovery of pump train failures during testing of the AFW pumps.

During AFW pump testing, a full flow recirculation test valve is opened to allow full AFW flow at the rated pump discharge pressure to flow to the condensate storage tank. Upon a system demand, the full flow test valve must be closed to allow AFW pump flow to discharge to the OTSGs. The full flow test valve is manually operated and is located in the vicinity of the associated AFW pump. The plant test procedure requires that an operator be present at the full flow test valve during testing. Because the associated AFW pump is running during the test, operator action is to close the full flow test valve will allow flow from the associated pump to go to the OTSGs. Turbine-driven pump recovery is considered for these failure if the operator takes action to close the full flow test valve within 10 minutes of system demand. The frequencies of operator error assigned for the event for the different time periods are:

a. O to 5 minutes: motor-driven pump train - 0.9; turbine-driven pump train - 0.9.
b. S to 10 minutes: motor-driven pump train - 0.1; turbine-driven pump train - 0.1. ,
c. 10 to 15 minutes: motor-driven pump train - 0.05; turbine-driven pump train - 0.1.
d. 15 to 20 minutes: motor-driven pump train - 0.01; turbine-driven pump train - 0.1.
e. Greater than 20 minutes: motor-driven pump train - 0.005; turbine-driven pump train - 0.1.
3. Recovery from the identified common cause failure of the AFW pump trains. This failure also involves the full flow test valves. The basic error consists of a common cause failure to reclose the test valves for both pump trains after pump testing. Recovery of this error prior to system actuation on demand is included in the frequency of system failure due to this cause. Recovery from this failure may also occur after system demand. Operator action to close the full flow test valves will allow pump flow to pass to the OTSGs.

The indications which are available to the operators in the control room to diagnose this problem are: test valve position indication, pump discharge pressure, and flow to the OTSGs. Recovery consists of sending an auxiliary operator to the AFW pump area to close the test 4 0176C022582

l l l l valves. The frequencies of operator error assumed for this event for the time periods of interest are:

a. O to 5 minutes - no recovery possible due to the short time that is available.
b. 5 to 10 minutes - 0.1.
c. 10 to 15 minutes - 0.1.
d. 15 to 20 minutes - 0.05. -
e. Greater than 20 minutes - 0.01.

An allowable outage time of 48 hours was chosen for these analyses. The 48-hour pump unavailability value is based upon the following considerations.

1. Recent work performed by Pickard, Lowe and Garrick, Inc., in suppg of PWRs a probabilistic reliability analysis for operating indicate that the mean unavailability o auxiliary feedwater pumps due to maintenance is 4.0 x 10-{ for plants with a 72-hour technical specification limit on allowable pump outage time.
2. A detailed review of the failure data of auxiliary feedwater systems in NPE indicates that 75% of all failures reported were repairable in less than 48 hours; an additional 14% were repairable in less than 72 hours, and the balance of the failures reported required longer than 72 hours for repair. A majority of the failures that required longer than 48 hours for repair were reported in plants that had: (1) no maximum allowable outage '

time for a single AFW pump or, (2) allowable outage times that were greater than 48 hours and less than 72 hours.

3. NUREG-0611 presents average pump outage times for allowable outage times of 24 hours and 72 hours. Using an average value of 13 hours for the times presented 7 hours + 19 hours 2

the unavailability of an AFW pump train due to maintenance is 3.9 x 10-3,

4. For operating PWRs, the periodic maintenance that is performed during plant operation requires less than 24 hours for completion (including post-maintenance testing).

For these reasons, the unavailability of a s{ngle AFW pump train due to maintenance is assigned a value of 4.0 x 10- for the 48-hour technical specificatic, limit. The results of these analyses are presented in the following table. 5 0176C022582 

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l TABLE 1. RESULTS OF ANALYSIS USING A 48-HOUR AFW PUMP TECHNICAL SPECIFICATION LIMIT t = 0 + 5 P(op error) = 1.0 Random 2.453 x 10-4 Maintenance MD (4,00 x 10- ) (5.730 x 10-3) 5 TD (4.00 x 10- ) (4.272 x 10-2) 2.292 x 10 4 Test 1,709 x 10 6 MD (3.47 x 10- ) (0.9)(5.730 x 10-3) TD (3.47 x 10- ) (0.9)(4.272 x 10-2) 1.791 x 10 5 1.335 x 10 6 Common Cause System 8.400 4.626 xx 10 10-4 t = 5 + 10 P(op error) = 0.5 Random 1.393 x 10-4 Maintenance MD (4.00 x 10- ) (5.730 x 10-3) 2.292 x 10-5 TD (4.00 x 10- ) (2.423 x 10-2) 9.642 x 10-5 Test MD (3.47 x 10- ) (0.1)(5.730 x 10-3) 1.990 x 10-7 TD (3.47 x 10- ) 7 Common Cause (0.1)(2.42g)x (8.4 x 10- (0,1) 10-2) 8.413 x 10 7 System 8.400 2.610 xx 10-10 4 t = 10 + 15 P(op error) = 0.1 Random 5.438 x 10-5 Maintenance MD (4.00 x 10- ) (5.730 x 10-3) 2.292 x 10-5 TD (4.00 x 10- ) (9.434 x 10-3) 3.774 x 10-5 Test MD (3.47 x 10- ) (0.05)(5.730 x 10-3) 9.948 x 10-8 TD (3.47 x 10- ) 3.276 x 10-7 Common Cause (0.1)(9.43g)x10-3) (8.4 x 10- (0.1) 8.400 x 10-7 System 1.163 x 10-4 6 0178C022582

__ = .- -. .. W-t TABLE 1 (continued) t = 15 + 20 P(op error) = 0.05 Random 4.377 x 10-5 5 Maintenance MD (4.00 x 10- ) (5.730 x 10-3) TD (4.00 x 10- ) (7.584 x 10-3) 2.292 x 10 5 Test MD (3.47 x 10- ) (0.01)(5.730 x 10-3 3.034 1.990 xx 10-10 8 TD (3.47 x 10- ) (0.1)(7.58g)x 2.633 x 10-7 10-3)) Common Cause (8.4 x 10- (0.05) 4.200 x 10-7 System , 9.773 x 10-5 t=> 20 minutes P(op error) = 0.005 Random 3.422 x 10-5 Maintenance MD (4.00 x 10- ) (5.730 x 10-3) 5 TD (4,00 x 10- ) (5.919 x 10-3) 2.292 2.368 xx 10-10 5 Test MD (3.47 x 10- ) 9.948 x 10-9 TD (3.47 x 10- ) (0.005)(5.730xig-)3) 2.055 x 10-7 Common Cause (0.1)(5.91g)x 10-(8.4 x 10- (0.01) 8.400 x 10-8 System 8.112 x 10-5 O I 7 0178C022582 ,

NOTES FOR TABLE 1 

       ,            1. The random contribution to system failure includes the effects of operator error in recovery of the motor-driven AFW pump upon a loss

,k of the diesel generator which supplies 1E bus 1A05 (2A05). s

2. Maintenance is quantified as follows:

f The unavailability of an AFW pump train due to maintenance is 1 multiplied by the frequency of system failure with that pump train outside of service. Q maint = 4.0 x 10"

3. Test is quantified as follows:

The unavailability at an AFW pump train due to testing is multiplied by the frequency of system failure with that pump train out of service and by the frequency of operator error for recovery. g , 15 minutes 1 hours 1 month 3 test 1 month 60 minutes x 720 hours perator error S N l l 1 i . ~ l' 8 l 0176C022582

~ REFERENCES

1. U.S. Nuclear Regulatory Commission, " Generic Evaluation of Feedwater Transients and Small Break Loss of Coolant Accidents in Westinghouse Designed Operating Plants," NUREG-0611, January 1980.
2. " Midland Plant Auxiliary Feedwater System Reliability Analysis prepared for Consumers Power Company" by Pickard, Lowe and Garrick, Inc., October 1980.
3. U.S. Nuclear Regulatory Commission, "Ree.ctor Safety Study: An Assessment of Accident Risks in U.S. Commercial Nuclear Power Plants," WASH-1400, 1975.
4. " Nuclear Power Experience," Volume PWR II, prepared by the Petroleum Information Corporation, Denver, Colorado,1970 through 1982.
5. PLG Calculations.

9 0176C022582 

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