NUREG/CR-2248 SAND 81-1625 co- w r _ Comanche Peak Steam Electric : Station, Units 1 and 2, ' Auxiliary Feedwater System Reliability Study Evaluation _ Prepared by B. J. Roscoe Sandia Phtional Laboratories Prepared for % [j \ U.S. Nuclear Regulatory 6- , '' Commission q, g _ y p ,[3 g g?). $ n - c E "arr+.ff' Cho!$h0$k5 PDR _ - - - - - _ _ _ _ - _ _ _ _ _ _ - _ _
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COMANCHE PEAK STEAM ELECTRIC STATION,UNITS 1 & … · NUREG/CR-2248 SAND 81-1625 co- w r _ Comanche Peak Steam Electric: Station, Units 1 and 2, ' Auxiliary Feedwater System Reliability
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NUREG/CR-2248SAND 81-1625
co- w r_
Comanche Peak Steam Electric: Station, Units 1 and 2,' Auxiliary Feedwater System
Reliability Study Evaluation
_
Prepared by B. J. Roscoe
Sandia Phtional Laboratories
Prepared for % [j \U.S. Nuclear Regulatory 6- , ''
Commission q, g _y
p ,[3g
g?). $ n- c
E
"arr+.ff'
Cho!$h0$k5PDR
_ - - - - - _ _ _ _ - _ _ _ _ _ _ - _ _
. . . . - - - . ,
NOTICE
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LIST OF FIGURESPage
1. Auxiliary Feedwater System Simplified Flow 8Diagram
2. Comparison of CPSES AFWS Reliability to 39Other AFWS Designs in Plants Using theWestinghouse NSSS
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!
Summary and Conclusions
The accident at Three Mile Island resulted in many studies which
outlined the events leading to the accident as well as those follow-
ing. One of the important safety systems involved in the mitigation
of such accidents was determined to be the Auxiliary Feedwater System -
(AFWS). Each operating plant's Auxiliary Feedwater System was
studied and analyzed. The results were reported in NUREG-0611.(1)
The licensee of each nor. operating plant was inatructed(2) to
perform a reliability analysis of his Auxiliary Feedwater System
for three transient conditions involving loss of main feedwater in
a manner similar to the study made by NUREG-0611. Texas Utilities
Generating Company (TUGC), the licensee for Comanche Peak Steam
Electric Station, submitted a reliability report (3) to the U. S.
Nuclear Regulatory Commission in January 1981. This report was
reviewed by Sandia National Laboratories. The following conclusions
resulted from the review:
1. Texas Utilities Generating Company has satisfactorily complied
with the requirement to make a reliability study of their AFWS.
2. The AFWS of the CPSES, Units 1 and 2, has high reliability
relative to the reliability of AFWSs of operating plants for
the first case event, Loss of Main Feedwater. Quantitatively,
the unavailability of the system for this event is approximately
2 x 10-5 per demand. Qualitatively, the system is automatically
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a
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initiated, highly redundant, has no. observed single point
vulnerabilities, and is tested periodically and following
realignment to ' demonstrate availability of flow path to thee
steam generators. Failure on demand is dominated by closure
of both valves in the suction lines. The unavailability for
!the second case event, Loss of Main Feedwater and Loss of
Offsite Power, is approximately 2.7 x 10-5 per demand, which
places reliability of 'the AFWS in the high range in comparison
with operating plants, if the reliability of the diesels is as
:
I high as .03. Failure on demand is dominated.by closure of
! both valves in the suction lines. The unavailability for the!
I third case event, Loss of Main Feedwater and Loss of All AC
', Power, is 1 x 10-2 which places the reliability in the medium.
range in comparison with operating plants. The turbine-driven
pump train has no identifiable ac power dependencies and is
automatically actuated. Failure on demand is dominated by
L.O. - Locked Open -t>lq Motor Operated COMANCHE PEAK S C.SFNAL SAFETY ANALYSG FtEPOrtTF.O. - Fails Open Pneumatic Operated Figure 1. Auxiliary Feedwater System UNITS I and 2
FAI - Fails As Is 4 Manual Operated
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_ _ _ _ _ - .- - - .-- _ -
;
-9
While the Conjensate Storage Tank is the preferred water supply,
another ANS Safet/ Class 3 alternate supply is provided. The
Auxiliary Feedwater System has the capability to draw suction from
the service water system (SWS) in the event of loss of the Conden-;
sate Storage Tank. Two normally closed, key-switch activated,
motor-operated butterfly valves in the SWS prevent polution of
the auxiliary feedwater by station service water.
,
Each motor-driven auxiliary feedwater pump is capable of delivering|j- 470 gpm, and the turbine-driven auxiliary feedwater pump is capablei
of dslivering 940 gpm to the steam generators. All three pumps
automatically deliver the flow within one minute following an
asixiliary feedwater actuation signal.
Each motor-driven pump normally feeds two steam generators. A nor-
mally closed interconnection between the motor-driven pump itischarge
lines permits either pump to feed all four steam generators. This
interconnection provides the operator with the means to maintain
the water level in all steam generators on a long-term basis follow-
ing a LOCA by operating either motor-driven puep. The pumps can be
manually started or stopped from the Control Room or the hot shutdown
panel.
The turbine-driven pump discharge line branches into four separate
lines each feeding one steam generator. Each of these lines is,
provided with a normally open, pneumatically operated feed regulator
The dominant (controlling) contributor to system unavailability was
found to be closure or blockage of both valves in the two suctiong
lines from the condensare storage tank.
Other important contributors to AFWS system unavailability were found |
|to be unscheduled maintenance of pumps and the testing of valves in j
the feedlines to each steam generator from the motor-driven pumps
and the turbine-driven pump.
The redundancy employed in the design of the CPSES AFWS was found
to be of the type whereby no obvious single faults (active components,
manual valves or human errors) were identified that dominate the
unavailability of the AFWS for a loss of main feedwater transient.
Case No. 2 - LMFW/ LOOP_
The dominant failure modes discussed above are not dependent on the
source of ac power (onsite or offsite) and thus are also the domi-
nant failure modes for this transient and the unavailability of the
AFWS. If the diesel generator failure probability were lower than
the used value, .03, Case 2 would show different failure modes thanm
Case 1. The slight reduction in AFWS system availability for this
transient is caused by a loss of redundancy in ac power sources
that results from a loss of of fsite power.
Case No. 3 - LMFW/LOAC
In this transient, loss of both offsite and onsite ac power is
postulated to occur with the coincident loss of main feedwater flow,
_ - _ _ _ _ - _ _ - _ _ .
(. - _.
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so that the available operating pump subsystems of the AFWS ara!
reduced to only the steam turbine-driven pump train. Thus, any#
single failures in this pump train alone would be sufficient to
fail the AFWS for this transient. The dominant contributors to
system unavailability for thie ;ase were found to include: (1) the
?.urbine-driven pump is offline for maintenance or testing..(2) the
valve in the pump suction line fails closed due to hardware fallute )1
or human error causing a loss of NPSH at the pump's suction.
SNL agrees with the above findings. No quantification of results,
!
was made by TUGC nor were results quantified in NUREG-0611. The
quantitative estimates were obtained subsequently from TUS andlchecked by SNL. For Case 1 the unavailability.of AFWS is 2.0 x 10-5'per demand while for Cases 2 and 3 the unavailability is 2.7 x 10-5
'
per demand and 1 x 10-2 per demand, respectively. These valves are
'plotted in Figure 2 along with the operating plant ratings which
were derived from NUREG-0611. The CPSES AFWS has high reliability
for Case No. 1, LMFW; high reliability for Case No. 2, LMFW/ LOOP;
and medium reliability for Case No. 3, LMFW/LOAC. Sandia agrees
with these ratings. "
There are two points which need to be resolved prior to operation.
These are:
(1) Test and Maintenance Procedures were not evaluated during the
review because they have not yet been accepted by the appli-
cant's manrgement. However, planned procedures have been
redundant, has no observed single point vulnerabitities, and
is tested periodically and following realignment to demonstrate
availability of flow path to the steam generators. Failure on
demand is dominated by closure of both valves in the suction
lines. The unavailability for the second case event is approxi-
mately 2.7 x 10-5 per demand, which places reliability in the
high range; this result obtains in Case 2 for a diesel generator
f ailure probability of .03 which is an acceptable value. Failure
on demand is dominated by closure of both valves in the suction
lines. The unavailability for the third case event is'1 x 10-2,
which places the reliability in the medium-to-high range. The TDP
train has no identifiable ac power dependencies and is automatically
actuated. Failure on demand is dominated by test and maintenance
outage.
6. Glossary of Terms
AC Alternating Current
ac alternating current
AFW Auxiliary Feedwater
AFWS Auxiliary Feedwater System
ANS American Nuclear Society
ASME American Society of Mechanical Engineers4
CPSES Comanche Peak Steam Electric Station
CST Condensate Storage Tank
DC Direct Current
_ ___ ._
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-42-
1
Glossary of Terms (Cont'd)
de direct current
FSAR Final Safety Analysis Report
ft feet
gpm gallons per minute
hr hour3
in inch
IEEE Institute of Electrical and Electronic Engineers
LAC Loss of all AC power
LMF Loss of Main Feedwater
LOCA Loss of Coolant Accident
LOSP Loss of Offsite Power
MDP Motor Driven Pump
NPSH Net Positive Suction Head
NRC Nuclear Regulatory Commission II
NSSS Nuclear Steam Supply System
psia pounds per square inch absolute
psig pounds per square inche gage
PWR Pressurized Water Reactor
RCS Reactor Cooling System
RHRS Residual Heat Removal System
S Siesmic )
SES Steam Electric Station
SFP Single Failure Point
_ _ _ _ _ _ _ - _ _ _ _ _ _ - _ _ _ _ _ _ _ _
_ _ _
-43-
Glossary of Terms (Cont'd)
SG Steam Generator
SNL Sandia National Laboratories
SSF Standby Shutdown Facilities
SWS Service Water System
T Temperature
TDP Turbine Driven Pump
Tavg Average Temperature
!TMI Three Mile Island 1
TUGC Texas Utilities Generating Company
TUS Texas Utilities Services
V Volt
F Degrees Fahrenheit
7. References
1. NUREG-0611 " Generic Evaluation of Feedwater Transients andSmall Break Loss-of-Coolant Accidents in Westinghouse-DesignedOperating Plants" dated January 1980.
2. Letter to all Pending Operating License Applicants of NuclearSteam Supply Systems Designed by Westinghouse and CombustienEngineering from D. F. Ross. Jr., Acting Director Division ofProject Management Office of Nuclear Reactor Regulation, Subject,Actions Required from Operating License Applicants of NuclearSupply Systems Designed by Westinghouse and Combustion Engineer-ing Resulting from the NRC Bulletins and Orders Task ForceReview Regarding the Three Mile Island Unit 2 Accident, dated
( March 10, 1980.
3. " Auxiliary Feedwater System Evaluation," Part II, E.1.1 of theFSAR for Comanche Peak Steam Electric Station, Unit Numbers1 and 2, dated January 30, 1981.
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4. Schedule _189 No. 1303-1 Title, " Review of Auxiliary FeedwaterSystem Reliability Evaluation Studies for Comanche Peak 182,Waterford 3, Watts Bar 1 and 2, and Midlevel' I and 2," dated
U.S. Nuclear Regulatory Commission (130 Copies for AN)Distribution Contractor (CDSI)7300 Pearl StreetBethesda, Maryland 20014
Armand Lakner -
Office of Nuclear Reactor RegulationU.S. Nuclear Regulatory CommissionWashington, D.C. 20555
3141 L. J. Erickson (5)3151 W. L. Garner '.3)
(For DOE / TIC)3154-3 C. H. Dalin (2 5)
(For NRC Distribution to NTIS)4400 A. W. Snyder4412 J. W. Hickman (5)4412 B. J. Roscoe (2)8214 M. A. Pound
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'U"U.S. NUCLE AR REGULATORY COM dlSSION" " > NUREG/CR-2248
BIBLIOGRAPHIC DATA SHEET SAND 81-1625O TITLE AND SUBTsTLE IAdd Volume No.. s!noornarierel 2. floave blank)Comanche Peak Steam Electric Station, Unit Nos. 1 and 2Auxiliary Feedwater System Reliability Study Evaluation 3. RECIPIENT'S ACCESSION NO.
7 AUTHOR (Si 5. DATE REPCRT COMPLETED
| YEARM ON THB. J. Roscoe June 1981
9 PE RFORMING ORGANIZATION N AME AND MAILING ADDRESS //nclum I,p Codel DATE REPORT ISSUEDMONTH | YEAR i
12 SPONSORING ORG ANIZ ATION N AVE AND M AILING ADDRE SS (inclum lep Co<8el0. PROJE C1/T ASK/ WORK UNIT NO
Division of Safety TechnologyOffice of Nuclear Reactor Regulation ii CONTRACT NOU.S. Nuclear Regulatory CommissionWashington, D.C. 205b5 NRC FIN A1303
13 TYPE OF REPOH T PE RIOD COV E RE D I/nclus,ve deres!
Technical15 SUPPLE MENTARY NO TE S 14. (Leave o/uk/
16 ABSTR ACT (200 words or less!
The purpose of this report is to present the results of thereview of the Auxiliary Feedwater System Reliability Analisis forComanche Peak Steam Electric Station, Unit Numbers 1 and 2.
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17 KE Y WQP PS AND DOCUME NT AN ALYSIS 1 ta DE SC RIP TORS
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