ML20034B963
| ML20034B963 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 04/25/1990 |
| From: | Owen T DUKE POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| -C90-79, 0-C90-0079, NUDOCS 9005010239 | |
| Download: ML20034B963 (8) | |
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' Duke Iburr Crur+any WWIOOOO Catawba Nuclear Station l'O lha 256 Clowr, S C 29710 -
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. DUKE POWCR April 25, 1990 Document Control Desk U..S. Nuclear Regulatory Commission Washington, D. C.
20555-
Subject:
' Catawba Nuclear Station:
_ Docket No. 50-413 PIR 0-C90-0079; IIR C90-024-0 Genticmen:
Attached is our. Problem Investigation Report 0-C90-0079, submitted concerning IDENTIFICATION OF-THE: INABILITY OF AUXILIARY FEEDWATER PUMPS TO TAKE SUCTION'FROM THE CONDENSER HOTWELL.
This incident was determined to be NRC non-reportable but has.been1 investigated and l
documented as a Special Report.
This event was considered to be of no significance with respect j
to the' health and safety of the public.
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Very truly yours, lth Tony B. Owen-Station Manager keb\\ REPORT.SP i
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Mr. S. D. Ebneter American Nuclear Insurers Regional Administrator, Region II c/o Dottie Sherman, ANI Library U. S. Nuclear Regulator Commission The Exchange, Suite 245 101 Marietta Street, NW, Suite 2900 270 Farmington Avenue Atlanta, GA 30323 Farmington, CT 06032 M & M Nuclear Consultants Mr. K. Jabbour 1221 Avenues of the Americas U
S. Nuclear-Regulatory Commission New York, NY 10020 Office of Nuclear Reactor Regulation Washington, D. C.
20555 INPO Records Center Suite 1500 Mr. W. T. Orders 4
1100 circle 75 Parkway NRC Resident Inspector Atlanta, GA 30339 Catawba Nuclear Station 9005010239 900425 i
i PDR ADOCK 05000413
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' -.c DUKE POWER COMPANY CATAWBA NUCLEAR STATION PROBLEM INVESTIGATION REPORT NO. 0-C90-0079-IDENTIFICATION-OF THE INABILITY OF AUXILIARY FEEDWATER PUMPS TO TAKE SUCTION FROM THE CONDENSER HOTWELL ABSTRACT
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On March 7, 1990 at approximately 1800 hours0.0208 days <br />0.5 hours <br />0.00298 weeks <br />6.849e-4 months <br />, with Unit 1 in Mode 5, Cold Shutdown,land Unit 2 in Mode 1, power Operation, Auxiliary Feedwater (CA). Pump 1A tripped on low' suction pressure during a functional-test of check valve 1CA-1 (CA Pumps Suction Check'From Hotwell).z The functional. test involved a pump-suction lineup from the Condenser Hotwell with the CA pump operating in the manual mode. -The cause of the event is attributed to a functional design deficiency due to an inadequate margin between existing Hotwell head pressure.
and the low suction. pressure pump trip set point.. The Unit 1 event, in which_a
. Technical Specification requirement is non-applicable for the Condensate Storage System'(CS)-, provided evidence that the similar condition existed on Unit 2,-
where the requirement-is specified. The Unit 2 CS System was. declared-
-inoperable. :The low suction pressure > pump trip.was bypassed by appropriate procedure changes in ordor to complete the Unit 1 functional test. Procedure changes and-compensatory measures were incorporated'into abnormal procedure AP/1&2/A/5500/06, Loss of Steam Generator Feedwater, to allow utilization of the Hotwell as a direct suction source for the CA pumps. This; incident was determined to be NRC non-reportable but has been investigated and documented as a Special Report.
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L U' PIR 0-C90-0079 LPage,2 BACKGROUND The Auxiliary Feedwater.[EIIS:BA)-(CA) System is a safety-related system which is designed to assure sufficient feedwater' supply to the steam generators
[EIIS HX) in the event of loss of the Condensate /Fecdwater_(EIISISD/SJ) (CM/CF)
System, to cooldown the Unit to allow initiation of Residual Heat Removal-
[EIIStBp) (ND) System operation.
The CA System operates in either the automatic or manual mode of operation..The
. automatic mode is initiated in response.to'any of the following signals loss of offsita power, safety injection, 1/4 and 2/4' low-low steam generator level logic, loss of both main feedwater pumps (EIIS p), and AMSAC (ATWS Mitigation System Actuation Circuit).- Manual mode is initiated by the Operator, either by.
manually' starting the pumps or by resetting the CA System controlu following an automatic start.
The CA pumps can take suction from three sources; the Condensate Storage (EIISIKA] (CS) System, the Nuclear Service Water [EIIS:BI] (RN) System, and the Condenser Circulating Water [EIISISG) (RC) System.
The CS System is the normal source, RN the assured source, and RC is reserved for Standby Shutdown Facility Events. Within the CS System, the Auxiliary Feedwater Condensate Storage Tank (CACST) and the Upper Surge Tanks (UST) are the only condensate' grade sources-suitable for direct supply to the CA pumps suction without having to manually defeat re-alignment interlocks to RN and RC, and breaking condenser vacuum. The
-CACST and the UST have a volume capacity of-42,500 and 85,000 gallons, repectively.
The Condeca 'r Hotwell provides an additional' 170,000 gallons of condenbate grade feedwtp.c supply. The CACST and the UST are available to the CA pumps in all modes of operation, with adequate net positive suction head available due to the elevation differences between the tanks and the pumps. For a postulated event requirlog prolonged operation of the CA System,~the contents of the Hotwell would be used to supply CA pump succlon following depletion of the CACST and the UST, rather than utilizing the raw water quality of the assured RN source. With a Hotwell pump available, the contents of the Hotwell when needed would be transferred to the UST. Otherwise, as-in the case of a Loss of Offsite power (LOOP), CA pump suction can be aligned directly to the Hotwell.
Iow suction pressure protection is provided for the CA pumps according to the=
following:
During an auto-start of the CA System coincident with low suction aressure,.
a swap to RN will occur when the auto-swap valve position switches are in their normal "AUT0" position.
During a manual start, or following reset of an automatic start, low suctica pressure will initiate a trip of the running CA pumps at the same setpoint as the RN swap.
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DUKE POWER. COMPANY / CATAWBA NUCLEAA STATION t
pIR 0-C90-0079 page,3 During any code of operation if the suction pressure drops below the RC pressure switch setpoints, the RC supply will align to the CA suction.
It is assumed that'these condensate grade water sources would be available for short term (7-8 hour). response to non-seimic. events, however this event showed' that premature swapover to RN could occur or that upon CA reset a CA pump trip occur when a large volume of condensate inventory remained.
Technical Specification 3.7.1.5 requires that:a minimum of 225,000 gallons of water be available in Modes 1, power Operation, 2, Startup;'and 3, Hot Standby,;
for Unit 2 only. A comparable specification is not applicable for Unit 1.
With the CS System inoperable, an action statement option includes demonstration of the operability of the RN backup supply and restoration of the CS System to operable status within seven days, s
EVENT DESCRIPTION On March 7, 1990, modified periodic test pT/1/A/4250/03A, CA pump 1A performance Test, was performed in order to conduct a functional / retest on check valve (EIIS:V] ICA-1 following corrective maintenance.
Restricted Change #27 to the PT was issued to allow the realignment of CA pump suction.from the UST to the condenser Hotwell, with condenser vacuum broken, in order to full stroke 1CA-1.
As the suction source was realigned to the Hotwell, operating CA pump 1A tripped on low suction pressure, contrary to the intended functional design of operation with adequate not positive suction head (NPSH) provided by the Hotwell.
In order to complete the functional test of ICA-1, it was.necessary to disable the pump trip circuitry for low suction pressure.
Restricted Change #28 to.
PT/1/A/4250/03A specifies the opening of sliding link Fal in control panel 1APWpTCP in order to block the CA pump 1A trip on low suction pressure on a I
manual pump start. Additionally as part of the test change, instructions were l-included for defeating the automatic swap of CA pump suction to the RC System l
makeup source.
(Automatic swap to RN is effectively defeated by the manual start.) Guidance on low pressure protection for the CA pumps in the Hotwell l
alignment was obtained from Design Engineering. To ensure that CA pump suction
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pressure does not reach a specified mininum value of 3.5 psig, the test L
procedure change also included cautionary guidance to maintain suction pressure greater than 4.0 psig. The swap to RN on low suction pressure interlock, coincident with a pump auto-start, is unaffected by the temporary circuit modification.-
l With the test procedure modified, the test.was repeated and successfully completed on March 8.
Test data of CA flow, suction pressure, and Hotwell level was collected at the request of Design Engineering.for the purpose of further evaluation.
The data was compiled as Design calculation CNC-1223.42-00-0022 and was used to generate the graph entitled 'CA pump suction pressure Based on
DUKE POWER COMPANY / CATAWBA NUCLEAR STATION pIR 0-C90-0079 paga,4-i r
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Hotwell Level and Flowrate.'
The graph provides specific guidance for the-purpose of ensuring that suction pressures are maintained above 3.5 psig.
The graph became an enclosure of abnormal procedure AP/1(2)/A/5500/06, Loss of Steam Generator Feedwater.
Following the test, the Unit 2 Condensate Storage System was declared inoperable at 0200 hours0.00231 days <br />0.0556 hours <br />3.306878e-4 weeks <br />7.61e-5 months <br /> due to the failure to meet the requirements of Technical Specification 3.7.1.5.
The corrective actions necessary to restore operability were identified, initiated, and completed in compliance with the ACTION statement of the Technical Specification.
The corrective actions involved various additions to Ap/2/A/5500/06 to provide guidance to operators for i
aligning the CA pump suction sources when the Hotwell pumps are not available.
i for transferring water from the Hotwell to the UST. Statements were-also added to caution operators of the automatic actions which could occur when the CA pumps are aligned to the Hotwell. The Unit 2 CS-System was declared operable on March 14 at 1753 hours0.0203 days <br />0.487 hours <br />0.0029 weeks <br />6.670165e-4 months <br />, i
CONCLUSION The cause of this incident is attributed to a functional design deficiency due to an inadequate operating margin between existing Hotwell head pressure and the low suction pressure pump trip setpoint._ The type of evolution that was conducted to functionally retest check valve ICA-1, was intended to be possible' even with the Condenser under normal vacuum. The actual condition would have prevented the use of the Hotwell as a CA pump suction source if appropriate-compensatory measures were not employed. The CA pumps were verified during pre-operational testing to be. functionally capable of receiving adequate suction directly from the Hotwell; however, this activity was not required as part of the initial test program. Since the pre-operational system check-out was i
performed with the low suction pressure trip interlock intentionally blocked, the system limitation was not evident. The. initial system check-out's were performed with the Condenser under vacuum, in which possible interference from the low suction pressure interlock was expected and therefore blocked.
It was known that in a situation of actual necessity for CA pump; suction on the Hotwell, that condenser vacuum would be previously broken as n' result of the-event or by associated mitigative actions, and would thereby provide adequate suction margin above the pump trip setpoint.
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Although numerous design deficiencies in general have been identified, there have been no similar previous occurrences to the discovered condition in this incident; therefore, this event is not considered a recurring event or problem.
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DUKE' POWER COMPANY / CATAWBA NUCLEAR STATION L
PIR 0-C90-0079
'Page,5 CORRECTIVE ACTION SUBSEQUENT 1)
Restricted Change #28 to PT/1/A/4250/03A was lssued to provide instructions for blocking the low suction pressure trip of CA Pump 1A
'for manual operation. Also included' wore cautionary statements-regarding a minimum suction pressure of 4.0 psig.
2)
The functional /retsat of; check valve ICA-1 using PT/1/A/4250/03A was-repeated and successfully completed.
3)
CA flow, pump suction pressure, and Hotwell level test data was gathered and provided to Design Engineering.
4)
The Unit 2 Condensate Storage System was' declared inoperable.
5)
Abnormal procedure AP/1(2)/A/5500/06 was revised to provide guidance to Operators for aligning the CA Pump suction sources when the Hotwell pumps are not available for transferring water from the Hotwell to the UST.
Statements were also added to caution Operators of the automatic actions which could occur when the CA pumps are aligned to the Hotwell.
PLANNED 1)
Performance, Operations, and Maintenance Engineering Services personnel will evaluate a recommendation from Design' Engineering of installing a duplicate set of pressure switches to those existing, which will monitor CA pump suction pressure in relation to a lower setpoint for the purpose of not positive suction head (NPSH) protection during modes of manual pump operation..The existing switches [EIIS XIS) would function for pipe'(EIIStPSP] brehk protection in cases of automatic operation.
SAFETY ANALYSIS The vital safety-related function served by the CA System during all postulated-occurrences requires the assurance of two trains supplied by a safety grade, seismically designed water source for pump suction to assure pump operability.
and function.
The safety-related suction function is accomplished via an automatic re-alignment feature to the RN. System.
In view of the consequences of unnecessary alignment of RN to the steam generators, maintaining a minimum condensato inventory is an important operational consideration. For chemistry F
concerns in events such as a blackout or loss of normal feedwater, the CA pumps are normally aligned to utilize the condensate quality water of the non-seismic
DUKE POWER COMPANY / CATAWBA N0 CLEAR STATION a
pIR 0-C90-0079 Page,6 o
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CACST, UST, and if necessary, the Condenser Hotwell. A combined water volune of
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225,000 gallons is to be available in Modes 1, 2, and 3, contained in the said-non-seismic sources, according to Unit 2 Technical Specification 3.7.1.5.
This value is based on a safe and orderly shutdown /cooldown with natural Reactor Coolant [EIIS:AB] System circulation.
For the purpose of this safety analysis, it is assumed that the contents'of the Condenser Hotwell would not have been avai..able as a non-safety CA pump suction source.during a postulated loss of feedwater/offsite power event., Since an automatic or manual start of the CA System is assumed in the FSAR Accident j
Analysis in conjunction with the LOOP, the LOSS OF NON-EMERGENCY AC POWER TO THE STATION AUXILIARIES event, described in FSAR Section 15.2.6, is considered the
'l bounding analysis for the subject condition.
The exclusion of the Hotwell storage capacity results in only the combined j
127,500 gallons of the CA CST and UST being available to " maintain the Reactor.
Coolant System at Hot Standby conditions for 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> followed by approximately 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> cooldown with steam discharge to the atmosphere concurrent with total loss-of-offsite power." This condition appears to have existed since initial Unit licensing.
i Prior to discovering the described functional discrepancy and since initial Unit licensing, alternative msans of avoiding an unanalyzed situation are considered L
to have been available. CA pump operability is maintained by compliance with t
tha surveillance requirement to verify the automatic availability of the seismically assured RN suction source, limited only.by the volune of the Standby i
Nuclear Service Water Pond (SNSWP) and RN water chemistry.
Since it was recognized during pre-operational' testing that blocking of the pump suction pressure interlock permitted " safe-if-monitored" operation of the CA l
pumps while aligned to the Hotwell, it is considered to have been a viable option at any time that it became necessary.to preclude the undesired swap to I
RN.
a To reiterate, the postulated unusable contents of the Hotwell are a result of a loss of power to the Hotwell pumps, which would normally be used to pump the Hotwell contents to the UST. Depending on the: circumstances surrounding the initiating 100P, methods are available by procedure for realigning offsite electrical power from the opposite unit, thereby restoring available power to the Hotwell pumps.
t Present operability of the Unit 2 Condensate Storage System has been addressed in the 10CFR50.59 evaluation which accompanied a necessary procedure retype for abnormal procedure AP/2/A/5500/06. Procedure revisions included provisions;for aligning the Hotwell to the CA Pump suction when the Hotwell pumps are not available for transferring water from the Hotwell to the UST.
Instructions were i
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DUKE POWER' COMPANY / CATAWBA NUCLEAR STATION
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pIR 0-C90-0079 Page,7-outlined for blocking the low pump suction pressure interlock as well as the automatic swap capability to the RC System piping.
Cautionary statements pertaining to pump protection and the remaining automatic interlocks were also added..(Similar changes,were,made to:the equivalent-Unit 1 procedure even though a similar Technical-Specification requirement does not' apply.)' These act. tons and demonstration of the operability of-the SNSWP as a backup supply to the CA pumps, constitute' full compliance with the Unit 2 Technical Specification action statement.
The health and safety of the public were unaffected by this' incident.l The incident was determined to be of no nuclear safety significance.
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