ML20212C820
| ML20212C820 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 11/30/1986 |
| From: | OMAHA PUBLIC POWER DISTRICT |
| To: | |
| Shared Package | |
| ML20212C817 | List: |
| References | |
| NUDOCS 8612310207 | |
| Download: ML20212C820 (26) | |
Text
6 4
9 OPPD FORT CALHOUN STATION UNIT 1 AUXII.IARY FEEDWATER SYSTEM RELIABILITY ANALYSIS NOVEMBER 1986 8612310207 861223 PDR ADOCK 05000285 PDR P
O TABLE OF CONTENTS Section Page 1.0 PURPOSE 1
2.0 SYSTEM DESCRIPTION 1
3.0 SCOPE AND ASSUMPTIONS 5
4.0 ANALYSIS DESCRIPTIONS 7
5.0 RESULTS 7
6.0 CONCLUSION
S 10 APPENDICES A
FAULT TREE DIAGRAM Al f
B COMP 0NENT FAILURE DATA B1 i
e s
- 1.0 PURPOSE The NRC, as.a part of the post-TMI review process, requested that a reliability analysis be performed on Auxiliary Feedwater Systems (AFWS) in accordance with the guidance of NUREG-0737 II.E.1.1 and the Standard Review Plan 10.4.9.
The Standard Review Plan (SRP), which defines the scope of the analysis, states that "An acceptable AFWS should have an unreliability in the range of 10-4 to 10-5 per demand based on an analysis using methods and data presented in NUREG-0611 and NUREG-0635".
The purpose of this analysis is to verify that the existing design of the Fort Calhoun Station AFWS does in fact meet the SRP reliability goal.
2.0 SYSTEM DESCRIPTION A schematic of the Fort Calhoun Unit 1 AFWS is presented in Figure 1.
The auxiliary feedwater system is considered to be that equipment required to store, pump and deliver makeup water to the steam generators to remove decay heat in the event the main feedwater system is not available. The system consists of one emergency feedwater storage tank, one motor-driven j-and one turbine-driven auxiliary feedwater pump, remotely operated flow control valves, interconnection piping to the main feedwater system and l-piping to the auxiliary feed nozzles in the steam generators, i
l' During system operation, feedwater from the emergency feedwater storage i
tank is pumped by either the motor-driven or the turbine-driven auxiliary feed pump, through either of two flow paths to the steam generators. One flow path connects to the main feedwater piping upstream of the feedwater regulating valves so that flow to either steam generator passes through the feedwater regulating valve and normal feed ring. The other flow path f
-connects directly to the auxiliary feed nozzles in the steam generators, l
through valves HCV-1107A/B and HCV-1108A/B.
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O The emergency feedwater storage tank is located in Room 81 of the auxiliary building and has a capacity of 60,350 gallons.
It can be filled with water from the condensate pump discharge, the demineralized water header # water plant), or the fire system. The tank must contain at least 55,000 gallons of water whenever the temperature of the RCS is greater than 300*F.
The tank is designed to have sufficient storage capacity to provide for the removal of heat from the steam generators, operating at a pressure of 1000 psia and receiving the maximum decay heat produced during the eight hours after a reactor trip.
The tank is normally maintained with a 1/2 to 1 psi nitrogen overpressure to exclude oxygen from the stored emergency feedwater to minimize system corrosion.
The tank is provided with a vacuum breaker in the event that a sudden temperature or volume change results in decreasing tank pressure below atmospheric.
The motor driven auxiliary feedwater pump is a horizontally mounted, eight stage, double volute, centrifugal pump. The pump is located on the lower level of the auxiliary building in Room 19. Water is gravity fed to the pump suction from the emergency feedwater storage tank. The power supply for the pump is the 4.16 KV Class lE AC Distribution System.
The turbine-driven auxiliary feed pump is a horizontally mounted two stage centrigugal pump.
It is located on the lower level of the auxiliary building in Room 19. Water is gravity fed to the pump suction from the emergency feedwater storage tank.
The turbine-drive unit is a sir #1e stage, velocity compounded, axial flow, impulse turbine with two sets of moving blades. The steam is supplied from either steam generator via connections upstream of the main steam isolation valves.
It passes through a stop valve (YCV-1045A or B) and an inlet strainer 3
4
before entering the unit through the governor valve, YCV-1045.
Control valves YCV-1045 and YCV-1045A/B are pneumatically operated two inch globe valves.
They are either automatically operated or manually operated.
The bearings of the turbine pump are forced feed lubricated and cooled. The unit is equipped with two lube oil pumps, an oil filter, an oil cooler, and associated control valves for controlling turbine speed. The lube oil cooler is supplied with cooling water from a connection on the pump casing. The water is returned to the pump suction piping.
Both pumps are cooled by the water they pump. To protect the pumps when starting or during other low-flow conditions, recirculation lines with automatically operated recirculation flow control valves FCV-1368 and 1369, are provided.
The valves are pneumatically operated globes. They can be either automatically or manually operated.
In automatic operation each valve is set to close automatically when flow through its pump is sufficient to prevent overheating and damage.
Flow to the steam generator may be delivered via the main feedwater piping or via the auxiliary feedwater nozzles. The normal flowpath to the steam generators, when the system is automatically activated, is through the auxiliary feedwater nozzles.
In the unlikely event that both of these paths are inoperable, the main feedwater paths are accessed by opening valve HCV-1384.
HCV-1384 is four inch motor operated gate valve.
The AFW flowpaths each contain two pneumatically operated control valves, HCV-1107 A&B and HCV-1108 A&B. The A valves are inside containment and act as isolation valves.
The B valves are outside containment and are typically used to control flow, a
4
The main feedwater flowpaths include the main feedwater bypass lines as well as the main feedwater lines. The paths include pneumatically operated flow control valves HCV-1101,1102,' 1105 and 1106. The main
.feedwater lines also include motor operated isolation valves HCV-1103, 1104, 1385 and 1386.
Table 2-1 summarizes the normal and fail-safe valve positions for all of the valves -included in the reliability analysis.
3.0 SCOPE AND ASSUMPTIONS The objective of this analysis is to determine the probability that the Fort Calhoun Auxiliary Feedwater System will activate on demand and will deliver the flow from at least one AFW pump to at least one steam gen-erator.
The AFW system boundary defined to include only equipment specifically part of the' AFW system or its associated flowpaths and ex-cludes auxiliary systems such as electrical power or air supplies.
In light of these definitions, the following assumptions have been made in performing the analysis:
1.
Recovery actions involving the positioning of manual valves are not included in the fault tree.
2.
The plant auxiliary systems, i.e., electrical power distribution systems, are assumed to be available and their dependencies are not modelled in the AFW system fault tree.
3.
AFW system unavailability due to testing was neglected since no component is aligned away from its safety position during test.
I 4.
AFW system unavailability due to common cause failures is not addressed in this analysis.
4 5
TABLE 2-1
.1 Valve Status Considerations n.
Motor Operated Valves Valve Normal Position Failtire Position HCV-1103 Open As Is, HCV-1104 Open As Is HCV-1384 Closed As Is 1
HCV-1385 Open.
As Is HCV-1386 Open As Is Air Operated Valves s
Valve Normal Position Failure Position FCV-1368 Open Open FCV-1369 Open Open FCV-1101 Open Closed FCV-1102 Open Closed HCV-1105 Closed As Is HCV-1106 Closed As Is HCV-1107A Closed Open HCV-11078 Closed Open HCV-1108A Closed Open HCV-1108B Closed Open YCV-1045 Closed Open i
YCV-1045A Closed Open YCV-10458 Closed Open Manual Valves 4
Valve Normal Status FW-339 Locked Open FW-1316 Locked Open FW-350 Locked Open FW-349 Locked Open FW-171 Locked Open FW-172 Locked Open l
FW-169 Locked Open i
FW-170 Locked Open FW-149 Open FW-150 Open FW-151 Open FW-152 Open FW-614 Open FW-615 Open 6
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D.
5.
The AFW automatic actuation signal is considered to be highly reliable.
Its unavailability has an insignificant impact on the unavailability of the AFW system.
6.
The delivery of AFW to either system generator is adequate for plant cooldown.
4.0 ANALYSIS DESCRIPTION The analysis can be divided into two stages:
assembly of the fault tree model and quantification of the system unavailability.
Quantification of the system unavailability was performed in two ways to provide more information. The first used mean values for the component failure probabilities, allowing computation of a point estimate unavailability for the system and importance rankings of the components. The second used log normally distributed values for the component failure probabilities, allowing computation of a distribution for the system unavailability.
5.0 RESULTS The fault tree model that was developed for this system is presented in Appendix A.
It is essentially divided into two parts that can be described as failure of the feedwater source (pumps) and failure of the flow paths to the steam generators.
The unavailabilities of the constituent components are presented in Appendix B.
These unavailabilities were used to quantify the top event of the AFW fault tree.
The results of the point estimate calculation indicate a mean unavail-ability of approximately 2.8x10-5 The top ten dominant cutsets are presented in Table 5-1 and the component importances are presented in Table 5-2.
l l
l 7
TABLE 5-1 Dominant Cutsets for Auxiliary Feedwater System
% of Total Cutset Descriotion Unavailability 1.
FW-6 Motor driven pump FW-6 fails to start 43.2%
FW-10 Turbine driven pump FW-10 fails to start 2.
FW-6 Motor driven pump FW-6 fails to start 32.4%
YCV-1045 Steam supply valve YCV-1045 fails to start 3.
FCV-1368 Recirc. control valve FW-1368 closed or plugged 5.7%
FW-10 Turbine driven pump FW-10 fails to start 4.
FCV-1369 Recirc. control valve FW-1369 closed or plugged 4.3%
FW-6 Motor driven pump FW-6 fails to start 5.
FCV-1368 Recire. control valve FW-1368 closed or plugged 4.3%
FCV-1045 Steam supply valve YCV-1045 fails to open 6.
FW-173 Check valve FW-173 plugged 1.4%
FW-10 Turbine driven pump FW-10 fails to start 7.
FW-173 Check valve FW-173 plugged 1.1%
YCV-1045 Steam supply valve YCV-1045 fails to open 8.
FW-6 Motor driven pump FW-6 fails to start 1.1%
FW-174 Check valve FW-174 plugged 9.
FW-350 Manual valve FW-350 closed or plugged 0.9%
FW-10 Turbine driven pump FW-10 fails to start
- 10. FW-171 Manual valve FW-171 closed or plugged 0.9%
FW-10 Turbine driven pump FW-10 fails to start l
8
- ~__ _-
i Table 5-2 Vesely-Fussel Importance Measures for Major Components Component Importance FW-6 Motor driven pump
.82 FW-10 Turbine driven pump
.52 YCV-1045 Steam supply throttle valve
.39 FCV-1368 Recirc. control valve pump FW-6
.11 FCV-1369 Recire, control valve pump FW-10
.05 FW-173 Check valve FW-6 discharge
.03 FW-350 Pump FW-6 suction isolation valve
.02 FW-171 Pump FW-6 discharge isolation valve
.02 FW-174 Check valve FW-10 discharge
.01 FW-349 Pump FW-10 suction isolation valve
.008
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4 9
The results of the distributed calculation can be summarized as follows:
Mean 2.3x10-b Median -
8.6x10-6 UpperBound(95% confidence) -
8.4x10-5 Lower Bound ( 5% confidence) 1.6x10-6 The distribution is a log normal with the upper bound defined as the ratio of the 95th to 50th percentiles.
A graph summarizing these results is presented in Figure 5-1.
6.0 CONCLUSION
S The objective of this analysis was to determine the reliability of the Forth Calhoun Unit 1 AFW system and to verify that it meets the SRP required reliability of 1x10-5 to 1x10-# per demand. The results of this analysis clearly show that the system does indeed meet the requirement.
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APPENDIX B Component Failure Data l
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,. C D 'm COMPONENT FAILURE DATA Point Est.
Evaluation Distributed Mean Median Error Values Values Factor Reference Manual Valves
-5 Left in adverse position 2.4x10-5 2.4x10 3
1 following maintenance Valve fails in adverse 3.6x10-5 3.6x10-5 3
1 position, undetected
-5
-5 6.0x10 6.0x10 3
-4
-4 Valve fails in adverse 4x10 4x10 3
2 position (closed), I.C.
-4 1x10-4 3
2 Valve fails in adverse 1x10 position (closed), 0.C.
Motor Driven Pump 10 1
3x10-3 1x10-3 Pump fails to start Turbine Driven Pump
-3
-3 Pump fails to start 4x10 1.5x10 10 1
Motor Operated Valves
-3
-3 Valve fails to open 3x10 1x10 10 3
-4
-4 Valve failed closed, 4x10 4x10 3
1*
undetected Pneumatic / Piston Operated Valves
-4 Valve failed closed, 4xic 4x10 3
1*
undetected
-3
-3 Valve fails to open 3x10 1x10 10 3
- Assume 6 month test interval B2
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REFERENCES:
1.
Calvert Cliffs Units 1&2 IREP Study Report.
2.
Reactor Safety Study, WASH-1400.
3.
NREP Guide, EGG-EA-5887, June 1982.
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