ML20126B505
| ML20126B505 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 12/15/1992 |
| From: | Mcmeekin T DUKE POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 92-20, NUDOCS 9212220113 | |
| Download: ML20126B505 (24) | |
Text
__ _____- _ ___
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Lade 1%ier Company T C A!.uuv%
AlcGuirr Nuclear (kneration ikpartment Vice l'rrsident 12700 flagers I?rry Roud (AfG0lA)
(704 sis-4800 llunteru die, NC 28078-8.985 (704)8754809145 DUKC POWER December 15, 1992 U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C.
20555
Subject:
McGuire Nuclear Station inplant Review Report Number 92-20 Gentlement Attached is Inplant Review Hoport Number 92-20.
This report is being submitted to the NRC as a voluntary special report to address a postulated scenario that could introduce air into the Auxiliary Foodwater suction piping.
Very truly yo rs,
/
/4(/4G T.C. McMookin TLP/bcb Attachmont xct Mr.
S.D.
Ebneter INPO Records Centor Administrator, Region II Suite 1500 U.S.
Nuclear Regulatory Commission 1100 Circlo 75 Parkway 101 Marietta St., NW, Suite 2900 Atlanta, GA 30339 Atlanta, GA 30323 Mr. Tim Reed Mr. P.K. Van Doorn U.S.
Nuclear Regulatory Commission NRC Resident Inspector Office of Nuclear Reactor Regulahlon McGuire-Nuclear Station Washington, D.C.
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e McGUIRE SAFETY REVIEW GROUP INPLANT REVIEW REPORT 1.
REPORT NUMBER:
92-20 2.
DATE OF REVIEW October 26, 1992 through December 10, 1992 3.
SUBJECT DESCRIPTION:
This Inplant Review is submitted to the NRC as a voluntary special report of the circumstances relating to the incident described in Problem Investigation Report (pIR) 0-M92-0406, Introduction of Air Into tha CA System Resulting From a Seismic Event.
The specific purpose of the review is to dotermine the cause of the incident and to ferm*.ilate solutions to prevent future problems of a similar nature.
4.
EVALUATION AND COMMENT On October 27, 1992, PIR 0-M92-0406 was issued by the McGuire safety Review Group to address a postulated scenario that could introduce air into the Auxiliary Feedwater (CA) suction piping. The concern was identified by thy McGuire Engineering Group during the review of calculations performed to verify Auxiliary Feedwater swapover pressure switch setpoints.
The calculations were part of the Design Basis Document (DBD) analysis review. During this review, questions were raised concerning the operability of the CA Pumps following a seismic event that resulted in a break in the normal CA pump suction line at the service / auxiliary building wall prior to pump start.
A piping break at this location would permit the draining of condensate (CM), which provides normal suction to the CA pumps. The resulting drain down would occur before the Nuclear Service Water (RN) Swapover Prescure Switches, which activate the assured makeup supply, could detect the drop in the pump suction pressure.
Upon cA pump startup, the air introduced into the pump supply header as a result of water drainage, would be forced into the pump inlet ahead of assured CA suction source-(RN) water, resulting in potential pump damage / inadequate pump performance.
e DPC/MNS INPLAttT REVIEW No. 92-20 PAGE 2 l
4.1 nackgrounds The CA system is a nuclear safety related system which is j
designed to provide a means of dissipating heat from the Reactor Coolant (NC) system if the CH system and Main Feedwater (CF) system are not available. The CA system is also used during normal startup and shutdown.
The CA system is provided with two motor driven (MD) pumps and_one terbine driven (TD) pump.
In addition to the three primary sources which supply the CA system sucticn, tle RN system provides the nuclear safety related assured CA system suction source.
CA pump suction diversity is provided by using several water sources and adequate valving for source-change. The CA pumps are normally supplied from a common header widc5 can be aligned to the upper surge tank, the CA condensate storage tank, or the condenser hot oell.
In accordance with the requirements set forth in Re ulatory Guide 1.70 and NUREG-0611, safety grade instrumentatiran is provided to detect loss of normal pump suction sources and swspover to the assured RN supply..This awapover lo
and instrumentation is required to ensure that long term safn*,y grade supply of water is available to mitigate the consequences of a design basis event.
When the CA pump suction pressure dro se below 2 pair for three seconds, RN will automatically. align to the CA suction header. A low suction pressure on the associated pump will cause the following valves to open CA PUMP PRESSURE SWITCil ISOLATION VALVE MDP A CAPS 5002 CA-15A CAPS 5350 RN-69A MDP B CAPS 5360.
CA-18B CAPS 5012 RN-162D j
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+
0 DPC/MNS i
INPLANT REVIEW No. 92-20 PAGE 3
)
TDP CAPS 5042 CA-86h CAPS 5370 RN-69A s
CAPS 5390 CA-116B 1
CAPS 5381 RN-162B CAPS 5044 CA-161C CAPS 5380 CA-162C l
l The RN system consists of Trains A and B which are normally l
aligned to Lake Norman. The RN system assured suction source to the CA system is available to each of the 3 CA system pumps by independent flow paths. Three independent flow paths are also available to the Turbine Driven Auxiliary Feedwater (TDCA) pump. Each flow path is isolated by 2 valves in series. The normal supply valves are motor operated and can be controlled either in the control Room or at local panels. One of the assured CA system suction sources for the TDCA pump is controlled at the Standby Shutdown Facility (SSF).
l Technical Specification (TS) 3.7.1.2 requires that at least 3 independent CA pumps and associated flow paths be operable in Modes 1 (Power Operation), 2 (Startup), and 3 (Hot Standby). The TDCA pump is required to be operable in Moden 1, 2, and, 3 with secondary steam pressure >/= 900 pounds.
With 1 CA pump inoperable, restore the inoperable pump to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or place the unit in at i
least Hot Standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Mode 4 (Hot Shutdown) within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
4.2 Description of Incidents McGuire Engineering Services personnel had completed the Design Basis Document for the CA system on or about October 1,
1992.
During performance of Design Study 50, Verification of Instrument Setpoints, Engineer A questioned the operability status of the CA pumps following a seismic event and prior to the starting of the pumps. The CA normal
.4 r
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DPC/MNS i
INPLANT REVIEW No. 92-20
]
[
PAGE 4 suction header is seismically qualified up to the junction j
of the servico/ auxiliary building wall (AA line).
In the 4
postulated scenario, a seismic event ruptures the CA pump suction piping prior to CA pump actuation, and automatic suction supply swapover to RN.
If the CA pumps had not yet started, no pipe auction would exist to prevent the normal j
supply water from draining out of the line break. When the
]
CA pumps then started, after detection of pump suction pressure < 2 poig for 3 seconds by the RN Swapover Pressure Switches, the waterleg remaining in the suction header would be insufficient to prevent the introduction of air into the pumps ahead of the assured suction source. Additionally, the pre-existing 2 peig setpoint that initiates the swapover to the assured source, after inclusion of the maximum post accident instrument inaccuracy and piping configuration, may not be adequate to assure activation of the swapover valves prior to the introduction of air into the pumps, if the normal suction sources are depleted. The introduction of air into the pumps could result in possible pump cavitation and the destruction / inadequate operation of the pumps.
Due to the time considerations involving calculations and modeling, Engineering personr.el elected to increase the setpoint of the CA feedwater pump pressure switches by one psig and to evaluate the CA suction piping to elevation 736 feet by Seismic Experience Walkdown Methods (SEWM). The new setpoint ensured that the static head alone would activatu the swapover to RN, thus eliminating the potential of air reaching the pumps in a low flow condition. The SEWM evaluated pipe provided the needed volume, and eliminated i
the potential of air reaching the pumps in a high flow condition.
This action was taken as a proactive measure to ensure current operability. The following setpoint recalibrations were performed:
1 I
i
DPC/MNS INP1. ANT REVIEW No. 92-20 PAGE 5 UNIT 1 Work Order Number Equipment Number 92081307 1MCAPS-5002 1LCAPS-5350 92081377 3MCAPS-5042 1MCAPS-5370 1MCAPS-5390 1MCAPS-5381 92081370 1MCAPS-5360 1MCAPS-5012 UNIT 2 Work Order Number Eguipment Number 92081358 2MCAPS-5002 2HCAPS-5350 92081366 2MCAPS-5360 2MCAPS-0012 92081400 2MCAPS-5042 2MCAPS-5370 2MCAPS-5390 2MCAPS-5381 i
The pressure switches were recalibrated from the current 2 psig to 3 peig, with the exception of 2 CAPS-5002 and 2 CAPS-5350 which were recalibrated from 3 poig to 4 pnig due to a r
difference in elevation.
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DPC/MNS INP1. ANT REVIEW No. 92-20 I
PAGE 6 During this recalibration, pressure switches 1/2 CAPS-5002, 4
1 5012, 5042, 5044, 5350, 5360, 5370, 5380, 5381, and 5390 I
were found to exhibit potentially excessive
)
inaccuracy / uncertainty in their as found calibration. This j
situation is addressed in PIR l-H92-0437 which was generated 1
on October 30, 1992. Component Engineering personnel are i
currently investigating this condition.
On October 29, 1992, Engineering Services personnel determined that the higher switch setpoint enwured current I
CA system operability based on calculation HCc-1223.42 j 0030, Rev.
1.
4 1
On November 24, 1992, Engineering Services personnel I
determined that the CA system had been past inoperable from I
initial startup until October 29, 1992, based on calculation Mcc-1223.42-00-0031.
4.3 Conclusions i
This incident is assigned a root cause of Functional Design i
Deficiency, because the margin of instrument inaccuracy of the pressure switches which detect a drop in pump suction pressure was too large to ensure assured pump suction source i
actuation as designed. The margin of error in this case is equal to +/- 1.31 pai. This resulted in the possibility of the pump suction pressure decreasing to 0.69 psi before automatic RN swapover.
l The CA system was determined to be past inoperable based on the previous CA suction pressure switch setpoint of 2 peig.
The following combination of events, in the initial portion of an accident sequence, was determined to cause potential loss of function to the CA systems 1.
Loss of CA caused by a seismic event, which causes l
a.
A pipe break which results in loss of the a
i
(
s
+
DPC/MNS INPLANT REVIEW No. 92-20 PAGE 7 normal CA suction source, but does not cause a loss of offsite power (i.e. no turbine driven pump auto start).
2.
A single failure of a CA motor driven pump In this particular combination of events, the flow rate in the CA suction path could have been such that the pressure switches would not have actuated in time to prevent air introduction by the operating CA MD pump and the air introduction could have then potentially damaged the pump or prevented it from functioning as designed.
The subsequent recalibration of the pressure switches precluded this type of event.
This scenario was discovered during the performance of the DBD for instrument setpoint calibration.
To date 45 DBD reviews have been performed by Engineering personnel.
No other instrument setpoint problems have been found.
4.4 Safety Evaluations The postulated scenario involved an earthquake coincident with events requiring CA system flow to aid in plant cooldown. The events requiring the CA system flod to aid in long term core cooling include, but are not limited to, loss of non-emergency AC power, loss of normal feedwater, feedwater line break, and small break loss of coolant accident (SBLOCA). An earthquake would potentially result in damage to the non-seismically qualified main feedwater and normal condensato sources rendering them unavailable as a CA water supply. With normal condensate sources lost, automatic swapover to the assured water source should take place when the suction pressure of the CA pumps falls below 2 psig.
It is postulated for the scenario in which only one motor driven pump is operable, the CA suction flow would be too low to accomplish the swapover to RN without the introduction of air to the pump. It is assumed these pumps i
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DPC/MNS t
INPLANT REVIEW No. 92-20 PAGE B l
would fail if subjected to this air.
There would not be sufficient flow to the SGs to remove decay heat.
Without
{
the necessary heat sink available, procedure EP/1,2/A/5000/13.1, Response To Loss of Secondary Heat sink, would direct the operators to establish feed and bleed l
cooling in the Reactor Coolant (NC) system using the Pressurizer Power Operated Relief Valves (PORVs) as a relief f
path. The feed and bleed process would supply cooling water to the reactor core to prevent fuel damage due to uncovering of the core. The cooling water would also supply a heat sink to remove heat from the core.
This would allow j
operations personnel time to take action to return the CA or j
CP pumps to cervice.
The sequences of the postulated scenario result in a total loss of the CA function, however this does not lead to core damage unless additional failures occur which would fail the operator ability to perform feed and bleed cooling.
The probability of these additional events occurring is t
approximately 1E-2 per demand.
Therefore, the likelihood that the problem identified with the CA System would lead to-core damage is approximately 4E-9 per year. The McGuire Probabilistic Risk Assessment (PRA) study had estimated that the normal core damage frequency for McGuire is 7.4E-5 per year. The additional sequence caused by the postulated CA l
scenario is so low that it would not be reported in the PRA report.
i 4
This incident is not Nuclear Plant Reliability Data Systems (NPRDS) reportable.
There were no personnel injuries, radiation overexposures, or uncontrolled releases of radioactivity to the environment 3
as a result of t his incident.
t 5.
Corrective Actions:
l l
t I
L
DPC/HNS INPLANT REVIEW No. 92-20 PAGE 9 Immediate None Subsequent 1.
The setpoints of the affected pressure switches were increased.
2.
The seismically unqualified portion of the "A Suction Piping was evaluated by SEWM.
Committed:
Engineering personnel will continue to gather information on the SEWN _ portion of the CA suction piping in order to formulate corrective actions to resolve this problem.
1
t DPC/ MMS INPIANT REVIEW No.
PAGE 10 ENCIDSURE 1 Prepared By:
J.M. Washam Dates December 10, 1992 Reviewed
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Dates
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Date
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W Date: __
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$ 0; I %.
W Date Date:
Dates Dates Approved By Jfh n17 7.
4 W M ates dDW
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D Hanithr, Safeh Review Distributions T.C. McHeekin
'O.D.
Gilbert J.W. Boyle P.R. Herran B.H. Hamilton B.F. Caldwell R.B. White J.N. Pope NRC Representative J.W. Foster.(as necessary)
CSRO R.P. Michael (as necessary)
OSRG Group Files MC-834.02 K.L. Crane ENCIDSURES:
1)
Safety Review Signature Sheet 2)-
References 3)
Corrective Action Schedule
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._. _ _ - ~ _.. -..
DPC/MNS INPI. ANT REVIEW No. 92-20 4
PAGE 11 4
ENCLOSURE 2 REFERENCES 1.
McGuire Nuclear Station Technical Specification 3.7.1.2 i
2.
Nuclear Generation Department Design Calculation HCC-1223.42 0030, current CA Operability.
3.
Nuclear Generation Department Design Calculation HCC-1223.42 0031, Past CA operability.
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f DPC/MNS INPLANT REVIEW No. 92-20 PAGE 12 l
ENCLOSURE 3 CORRECTIVE ACTION SCHEDULE 1
Corrective Person (s)
Person (s)
Action Contacted Assigned To Due Date J.R.
Pring T.D. Curtis June 1, 1993 s
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Dube Ibuer Company T C AI uu ns 61cGuire Nuclear Generation Department Vice President 12700llagers l' rry Road (AIGotA)
(104)STS 4M4 e
Iluntersalle, hC 2$078 895S (704)875 4809 th 1.
i DUKE POWER 4
l-December 15, 1992
}
U.S. Nuclear Regulatory Commission Document Control Desk
-l l
Washington, D.C.
20555 i
Subject:
McGuire Nuclear Station j
Inplant Review Report Number _92-20 i
u-j Gentlemen:
l' i
Attached is Inplant Review Report Number 92-20.
This report is being.
submitted to the NRC as a voluntary special report to address a i
postulated scenario that could introduce air into the Auxiliary i
Feedwater suction piping.
i-l Very truly yo rs, L
9(MJ/
T.C. McMeekin l
TLP/bcb Attachment i
xc Mr.
S.D. F.bneter INPO Records Center' Administrstor, Region II' Suite 1500 U.S.
Nuclrar Regulatory Commission 1100 Circle _75 Parkway l
101-Marioita St.,-NW, Suite 2900 Atlanta,-GA_ 130339_
j Atlanta,JJ.A 30323 Mr. Tim RNd Mr.
P.K._ Van Doorn-U.S..Nuclu r-Regulatory Commission NRC Resident Inspector-Office of Nuclear Reactor Regulation-McGuire Nuclear Station.
Washingtoo, D.C.
-20555:
i s
me.m e n w
bxc: T.S.
Barr B.L. Walsh R.C. Futrell (CNS)
R.L. Gill R.E.
Itall P.R. lierran R.G. Ilull R.C. Norcutt M.E. Patrick (ONS)
G.li. Savage R.O.
Sharpe G.B.
Swindlehurst li.B. Tucker R.L. Weber W.M. Sample D.B. Cook NSRB Support Staff (EC 12-A) l t
yr-e #- v
i j
McGUIRE SAFETY REVIEW GROUP INPLANT REVIEW REIVRT l.
REPORT NUMBER:
92-20 2.
DATE OF REVIEW October 26, 1992 through December 10, 1992 3.
SUBJECT DESCRIPTION:
This Inplant Review is submitted to the NRC as a voluntary special report of the circumstances relating to the incident described in j
Problem Investigation Report (PIR) 0-M92-0406, Introduction of Air Into the CA System Resulting From a Seismic Event.
The specific purpose of the review is to determine the cause of the incident and to formulate eulutions to prevent future problems of a similar nature.
4.
EVALUATION AND COtMENT:
On October 27, 1992, PIR 0-M92-0406 was issued by the McGuire Safety Review Group to address a postulated scenario that could introduce air into the Auxiliary Feedwater (CA) suction piping.
The concern was identified by the McGuire Engineering Group during the review of calculations performed to verify Auxiliary Feedwater awapover pressure switch setpoints. The calculations were part of the Design Basis Document (DDD) analysis review. During this review, questions were raised concerning the operability of the CA Pumps following a seismic event that resulted in a break in the normal CA pump suction line at the service / auxiliary building wall prior to pump start. A piping break at this location would permit the draining of condensate (CH), which provides normal suction to the CA pumps. The resulting drain down would occur before the Nuclear Service Water (RN) Swapover Pressure Switches, which activate the assured makeup supply, could detect the drop in the pump suction pressure.
Upon CA pump startup, the air introduced into the pump supply header as a result of water drainage, would be forced into the pump inlet ahead of assured CA suction source (RN) water, resulting in potential pump damage / inadequate pump performance.
4 i
4 9
]
DPC/MNS INPLANT REVIEW No. 92-20 PAGE 2 4
4.1 Hackgrounds l
The CA system is a nuclear safety related system which is designed to provide a means of dissipating heat from the Reactor Coolant (NC) system if the CH system and Main Feedwater (CF) system are not available. The CA system is 1
also used during normal startup and shutdown. The CA system is provided with two motor driven (MD) pumps and one turbine
]
driven (TD) pump.
In addition to the three primary sources which supply the CA system suction, the RN system provides the nuclear safety related assured CA system suction source.
i CA pump suction diversity is provided by using several water sources and adequate valving for source change.
The CA pumps are normally supplied from a common header which can i
be aligned to the upper surge tank, the CA condensato storage tank, or the condenser hotwell.
In accordance with the requirements set forth in Regulatory Guide 1.70 and NUREG-0611, safety grade instrumentation is provided to detect loss of normal pump suction sources and swapover to the assured RN supply. This awapover logic and instrumentation is required to ensure that long term safety l
grade supply of water is available to mitigate the consequences of a design basis event.
When the CA pump suction pressure drops below 2 peig for three seconds, RN will automatically align to the CA suction header. A low suction pressure on the associated pump will cause the following valves to open CA PUMP PRESSURE SWITCH ISOLATION VALVE MDP A CAPS 5002 CA-15A CAPS 5350 RN-69A MDP B CAPS 5360 CA-18B CAPS 5012 RN-162B l
l l
l
i DPC/MNS INPLANT REVIEW No. 92-20 l
PAdB 3 l
TDP CAPS 5042 CA-86A CAPS 5370 RN-69A CAPS 5390 CA-116B CAPS 5381 RN-162B CAPS 5044 CA-161C l
CAPS 5380 CA-162C t
The RN system consists of Trains A and B which are normally aligned to Lake Norman. The RN system assured auction source to the CA system is available to each of the 3 CA system pumps by independent flow paths. Three independent flow paths are also available to the Turbine Driven Auxiliary Feedwater (TDCA) pump.
Each flow path is isolated by 2 valves in series. The normal supply valves are motor operated and can be controlled either in the Control Room or 4
at local panels. One of the assured CA system suction sources for the TDCA pump is controlled at the Standby Shutdown Facility (SSF).
Technical Specification (TS) 3.7.1.2 requires that at least 3 independent CA pumps and associated flow paths be operable in Modes 1 (Power Operation), 2 (Startup), and 3 (Hot Standby). The TDCA pump is required to be operable in Modes i
1, 2, and, 3 with secondary steam pressure >/= 900 pounds.
With 1 CA pump inoperable, restore the inoperable pump to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or place the unit in at least Hot Standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Mode 4 (Hot Shutdown) within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
i 4.2 Description of Incident:
McGuiro Engineering Services personnel had completed the Design Basis Document for the CA system on or about October 1, 1992. During performance of Design Study 50, l
Verification of Instrument Setpoints, Engineer A questioned the operability status of the CA pumps following a seismic-event and prior to the starting of the pumps.
The CA normal l
l i
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e l
DPC/HNS INPLANT REVIKW No. 92-20 PAGE 4 i
l suction header is seismically qualified up to the junction Q
of the service / auxiliary building wall (AA line).
In the postulated scenario, a seismic event ruptures the CA pump suction piping prior to CA pump actuation, and automatic d
suction supply swapover to RN.
If the CA pumps had not yet d
started, no pipe suction would exist to prevent the normal supply water from draining out of the line break.
When the CA pumps then started, after detection of pump suction pressure < 2 peig for 3 seconds by the RN Swapover Pressure Switches, the waterleg remaining in the auction header would j
be insufficient to prevent the introduction of air into the j
pumps ahead of the assured suction source.
Additionally, the pre-existing 2 psig petpoint that initiates the evapover to the assured source, after inclusion of the maximum post accident instrument inaccuracy and piping configuration, may not be adequate to assure activation of the swapover valves prior to the introduction of air into the pumps, if the normal suction sources are depleted. The introduction of air into the pumps could result in possible pump cavitation and the destruction / inadequate operation of the pumps.
J l
Due to the time considerations involving calculations and modeling, Engineering personnel elected to increase the setpoint of the CA feedwater pump pressure switches by one l
peig and to evaluate the CA suction piping to elevation 736 feet by Seismic Experience Walkdown Methods (SEWM).
The new setpoint ensured that the static head alone would activate the swapover to RN, thus eliminating the potential of air reaching the pumps in a low flow condition. The SEWM i
evaluated pipe provided the needed volume, and eliminated the potential of air reaching the pumps in a high flow condition, s
This action was taken as a proactive measure to ensure current operability. The following setpoint recalibrations were performed
_ _.. _ _ - -..~..--._ -__,_.. ~ ~
_.=.
1 4
]I DPC/MHS i
INPLANT REVIEW No. 92-20 PAGE 5 Y
UNIT 1 i
)
Work Order Number Equipment Number i
92081307 1MCAPS-5002 1MCAPS-5350 92081377 1MCAPS-5042 5
1MCAPS-5370 3MCAPS-5390 1MCAPS-5381 92081370
- 1MCAPS-5360 1MCAPS-5012 1
)
UNIT 2 i
Work Order Number Equipment Number 92081358 2MCAPS-5002 2MCAPS-5350 92081366 2MCAPS-5360 2MCAPS-5012 92081400 2POAPS-5042 JMCAPS-5370 2MCAPS-5390 2MCAPS-5381 l
The pressure switches were recalibrated from the current 2 psig to 3 psig, with the exception of 2 CAPS-5002 and 2 CAPS-5350 which were recalibrated from 3 peig to 4 psig due to a difference in elevation.
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DPC/KNS INPLANT REVIEW No. 92-20 PAGE 6 1
During this recalibration, pressure switches 1/2 CAPS-5002, 5012, 5042, 5044, 5350, 5360, 5370, 5380, 5301, and 5390 were found to exhibit potentially excessive ina: curacy / uncertainty in their as found calibration.
This situation is addressed in PIR 1-H92-0437 which was generated
]
on October 30, 1992. Component Engineering personnel are I
currently investigating this condition.
i on October 29, 1992, Engineering Services personnel determined that the higher switch setpoint ensured current 4
CA system operability based on calculation HCC-1223.42 0030, Rev. 1.
on November 24, 1992, Engineering Services personnel determined that the CA system had been past inoperable from initial startup until October 29, 1992, based on calculation HCC-1223.42-00-0031.
4.3 conclusion
This incident is assigned a root cause of Functional Design Deficiency, because the margin of instrument inaccuracy of the pressure switches which detect a drop in pump suction pressure was too large to ensure assured pump suction source i
actuation as designed. The margin of error in this case is equal to +/- 1.31 pai. This resulted in the possibility of the pump suction pressure decreasing to 0.69 psi before l
automatic RN swapover.
The CA system was determined to be past inoperable based on the previous CA suction pressure switch setpoint of 2 psig.
The following combination of events, in the initial portion I
of an accident sequence, was determined to cause potential loss of function to the CA systems 1.
Loss of CA caused by a seismic event, which l
causes:
l l
A pipe break which results in loss of the a.
l t.
DPC/HNS INPI. ANT REVIEW No. 92-20 PAGE 7 normal CA suction source, but does not cause a loss of offsite power (i.e. no turbine driven pump auto start).
2.
A single failure of a CA motor driven pump In this particular combination of events, the flow rate in the CA suction path could have been such that the pressure switches would not have actuated in time to prevent air introduction by the operating cA MD pump and the air introduction could have then potentially damaged the pump or prevented it from functioning as designed. The subsequent recalibration of the pressure switches precluded this type of event.
This scenario was discovered during the performance of the DBD for instrument setpoint calibration.
To date 45 DBD reviews have been performed by Engineering personnel. No other instrument setpoint problems have been found.
4.4 Safety Evaluation:
The postulated scenario involved an earthquake coincident with events requiring CA system flow to aid in plant cooldown.
The events requiring the CA system flow to aid in long term core cooling include, but are not limited to, loss of non-emergency AC power, loss of normal feedwater, feedwater line break, and small break loss of coolant accident (SDLOCA). An earthquake would potentially result in damage to the non-seismically qualified main feedwater and normal condensate sources rendering them unavailable as a CA water supply. With normal condensate sources lost, automatic swapover to the assured water source should take place when the suction pressure of the CA pumps falle below 2 peig.
It is postulated for the scenario in which only one motor driven pump is operable, the CA suction flow would be too low to accomplish the swapover to RN without the introduction of air to the pump. It is assumed these pumps
4 DPC/MNS INPLANT REVIEW No. 92-20 PACH 8 would fail if subjected to this air.
There would not be sufficient flow to the SGs to remove decay heat.
Without the necessary heat sink available, procedure i
EP/1,2/A/5000/13.1, Response To Loss Of Secondary Heat Sink, would direct the operators to establish feed and bleed cooling in the Reactor Coolant (NC) system using the Pressurizer Power Operated Relief Valves (PORVs) as a relief path. The feed and bleed process would supply cooling water to the reactor core to prevent fuel damage due to uncovering j
of the core.
The cooling water would also supply a heat j
sink to remove heat from the core. This would allow i
operations personnel time to take action to return the CA or l
CF pumps to service -
i The sequences of the postulated scenario result in a total loss of the CA function, however this does not lead to core damage unless additional f ailures occur which would f ail the operator ability to perform feed and bleed cooling. The probability of these additional events occurring is approximately lE-2 per demand. Therefore, the likelihood that the problem identified with the CA System would lead to core damage is approximately 4E-9 per year. The McGuire Probabilistic Risk Assessment (PRA) study had estimated that the normal core damage frequency for McGuire is 7.4E-5 per year. _The additional sequence caused by the postulated cA scenario is so low that it would not be reported in the PRA 4
report.
1 This incident is not Nuclear Plant Reliability Data Systems (NPRDS) reportable.
4 There were no personnel injuries, radiation overexposures, or uncontrolled releases of radioactivity to the environment as a result of this incident.
U 5.
Corrective Actions:
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i DPC/MNS j
INPIANT REVIEW No. 92-20 PAGE 9 Immediates None a
subsequent:
1.
The setpoints of the affected pressure switches were increased.
1 2.
The seismically unqualified portion of the j
CA Suction Piping was evaluated by SEWM.
1 Committed:
Engineering personnel will continue to gather information on the SEWN portion of the CA suction piping in order to formulate corrective actions to resolve this problem.
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