ML20127E019
| ML20127E019 | |
| Person / Time | |
|---|---|
| Site: | McGuire  |
| Issue date: | 09/09/1992 |
| From: | Mcmeekin T DUKE POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9209150261 | |
| Download: ML20127E019 (13) | |
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11 l-I)ake Mgr Cmpany T C W wtEUN Mc&.re Nuclear Gewuth,n ikportment the l>rsudent 12700llagers inty %d tMG01A)
(704)$i5 4h00 Iluntenville. NC23078 iM5 (i)4)bi5 4M9 fu DUKEPOWER September 9, 1992 U.S. Nuclear Regulatory Commission Document Control Desk Washirigton, D.C.
20555
Subject:
- Inplant Review 92-06' h
Gentlemen Attached you will find Inplant Review 92-06.
This report is being i
submitted as a voluntary special report.
The report describes the circumstanced relating to an Unusual Event which was declared on April i
21, 1992.. The event was caused by a loss of Train B of the Solid l
State Protection System in conjunction with a Technical Specificatloa related load reduction.
This event is considered to be of no significance with respect to the health and safety of the public.
'Very truly yours, Nb T.C. McMeekin TLP/bcb L~
Attachraent xc:
Mr.
S.D.
Ebneter INPO Records Center Administrator, Region II Suite 1500 L
.U.S.
Nuclear Regulatory Commission-1100 Circle 75 Parkway L
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 Of fice. of Nuclear Reactor Regulati.n McGuire Nuclear Station Washington, D.C.
20555-9209150s.'61 920909 PDR ADOCK 05000369 o?J)
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MedUIRE SAFETY REVIEW GROUP INPLANT REVIEW REPORT 1.
REPORT NUMBER:
92-06 i
2.
DATE OF REVIEW:_ April - Scutember, 1992 3.
SUBJECT DESCRIPTION:
This Inplant Review Report is beAng submitted to the NRC as
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4 a voluntary Special Report of the circumstances relating to an Unusual' Event which was declared on April 21, 1992, and documented on-Problem Investigation Report (PIR) 1-M92-0002.
L The event was caused by a loss of Train E of the Solid State Protection-System (SSPS).
The specific purpose of tha review was to determina the cause of the event and possible solutions to prevent further problems of the type that occurred during the event.
4.
EVALUATION AND COMMENT:
7 Abstract On April _ 21,-1992, at 1110, an Unusual Event was declared because Unit 1LTrain B of the SSPS was inoperable, and a load reduction was initiated por Technical Specifications (TSa).
At 1127, Operations (OPS) personnel made the required notification to the state and county warning points.- Unit 1 was in Mode 1-(Power Operation) at 90
. percent-power prior to the ovent.
At 0900, OPS Cortrol Room (CR) personne1'had started receiving multiple alarms on multiple CR annuncle'orn.
The erroneous alarms were subsequently.' traced o a defective circuit card within the SSPS.
At the time, itJwas believed Lhat the SSPS failure was due to the elevated temperature in the CR which had f
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i DPC/MNS INPLANT REVIEW No. 92-06 PAGE 2 of 12 tesulted from a CR dir llandling Unit (AHU) chiller failure i
earlier that day.
A load reduction was commenced at 1100 because the SSPS could not be repaired within the time allowed by TSs.
The SSPS was later repaired, the load I
decrease -was secured, and the Unusual Ever.' was terminated et 1316 _ This_ event is assigned a cause of Equipment Failure because of the failed circuit card within the SSPS.
The. circuit card was sent to Westinghouse for repair and failure analysis.
Background
The SSPS takes digital inputs from the 7300 Process Control system and nuclear instrumentation channels corresponding to conditions (normal / abnormal) and combines these signals in the required logic-combination and generates a trip cignal to the Reactor Trip circuit breakers when the necessary combination of signals occur.
The system-also providev
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input signals to annunciators, etatus lights, and the Operato.i Aid Computer for phrtial and full trip functions and the status of the various blocking, permissive and actuation-functions.
TS Action Statement No._14, Table 3.3-3, in part, states:
"With the number of operable channels one less than the minimum channels operable requirement, be in at least Hot Standby within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Cold Shutdown within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />",
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Notification of an. Unusual Event is required when events are
. in the process of' occurring 'r have occurred which indicate
. a potelitial degradation of the level of safe *.y of the plant.
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.DPC/MNS INPLANT REVIEW No. 92-06 PAGE 3 of 12 Procedure RP/0/A/5700/00, Classification Of Emergency, requires, in part, an Unusual Event be declared, if less than the minimum channels of Engineered Safety Features (ESP) function are operable
.d a load reduction or plant cool down is laitiated-in accordance with TSs.
The Control Area Ventilation (VC) system is designed to maintain the environment in the CR within acceptable temperature limits for safe occupation, to perform maintenance, and equipment operation Two redundant 100 l
percent AllUs are provided for the CR.
TS 3/4.7.6 requires 2 l'
independent VC systems to be operable in all modes of operation.
Description Of Event On December 17, 1991, Nuclear Station Modification (NSM) 52125 was completed which added an oil reclaim line to CR VC Chiller-B.
The installation of the oil reclaim line is documented on work request 952841.
In order to meet the requirements of TS 3/4.7.6, and verify operability of CR VC
-Chiller B, a pressure test was su_sequently performed.
The pressure test of CR VC Chiller B incluoed a visual inspection and a bubble leak test of the isolation valves to tru) lines and fittings added by NSM MG-52125.
The leak test, as. documented on work request 98894, was performed l_
both with the chiller off and at a pressure of approximately and with the chiller running.
Both teats were 75 psi, 1
completed with satisfactory results, and no leaks observed.
CR VC Chiller B was then returned to operable status,
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however, the 031 reclaim line was intentionally left isolated from the~ system.
4 DPC/MHS
.INPLANT REVIEW No. 32-06 PAGE 4 of 12 During the time period of December 17, 1991 through April
- 21, 1992, the VC system was periodically swapped between CR VC Chiller A and CR VC Chillar B approximately every two weeks.
On April 13, 1992, the functional verification of the oil reclaim system on CR VC Chiller B was completed as directed by temporary procedure TN/0/A/2125/00/AM1, Implementation Procedure For NSM MG-52125.
On April 21, 1992, CR VC Chiller A had been running for approximatelyLtwo weeks; therefore, OPS personnel began the routine swap from CR VC Chiller A to CR VC Chiller B.
Heating,' Ventilation, and Air Conditioning (HVAC) crew personnel were on standby near the CR VC chiller equipnient in case a problem developed.
At 0848, an OPS person started CR VC Chiller B.
' This was the first t*me CR VC Chiller B was placed in service with the new oil reclaim line in service.
At 0852, CR VC Chillei B tripped on low freor, pressure.
HVAC personne] immodlately started troubleshooting CR VC Chiller B.
At 0500, multiple spurious alarms were received on CR Annunciator. panels 1AD1, 1AD2, 1AD3, 1AD4, 1 ADS, 1AD6, and 1 F01. - OPS CR personnel noticed that the temperature in the CR was' rising and referred to procedure AP/0/A/5500/39, CR L
High Temperature. - Priority E wJrk request 147384 was generated to investigate the VC system chiller problem.
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At 0901, OPS CR personnel observed a temperature of 79 degrees F near.the SSPS ce.binets.
Instrument and Electrical (IAE) and Maintenance Engineering Services (MES) personnel
- were notified to investigate the annunciator spurious alarm l
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Dh'C/MNS INPLANT REVIEW No. 92-06 i
PAGE 5 of 12 problem.
CR VC Chiller A was restarted to return VC system operability, while MES and IAE personnel investigated the annunciator problem.
At the time, OPS CR personnel believed that the annunciator problem was due to the elevated CR temperature.
IAE personnel opened the 7300 cabinet doors to allow additional air circulation and cool the cabinet r
interiors.
i At 0914, MES personnel notified CPS CR personnel that a failed demultiplexer circuit board in SSPS Train B had caused the spurious annunciator alarms.
SSPS Trajn B was declared inoperable and the output was inhibited which
. cleared the spurious annunciator alarms.
MES and IAE-personnel continued to investigate why tne demultiplexer circuit board had failed.
f By'0915, the temperature in the CR had started to return to aormal and work request 147303 was written to repair Train B SSPS.
During troubleshooting and repair activities, MES personnel determined 1that a: procedure change was required to procedure IP/0/A/3010/07, Procedure For Troubleshooting The SSPS, to prevent: generating a Reactor Trip signal._IAE and MES hli personnel were nct sure that the required procedure change could be implemented, and SSPS Train B su"1oguently repaired within the time allowed prior to commencing-a unit shutdown.
This'was discussed with OPS personnel and at - 1100, a load reduction of 6 megawatts (MW) per minute was initiated to meet TS requirements.
At_approximately 1110 to 1115, an Unusual Event was declared
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e DPC/MNS INPLANT REVIEW No. 92-06 PAGE 6 of 12 in accordance with the requirements of procedure-RP/0/A/5700/00, because Unit 1, Train B SSPS was inoperable which resulted in loss than the minumum chann la of ESF functions operablo, and a load reduction or plant cool down in accordance with TSs had been initiated.
At 1127, Operations (OPS) personnel made the required notification to the state and county organizations.
At 1220, the load decrease was reduced to 2 MWs por minuto.
At 1230, the=1oad decrease was secured at 680 MW.
L By'1315, the demultiplexor circuit board ir Train B SSPS was replaced.
Train a SSPS was returned to service and declared operable and, at-1316, the Unusual Event was terminated.
By 2130, all. troubleshooting and repairs were complete on CR VC Chiller a and it was subsequently returned to oporable status.
On May'6, 1992, a meeting was held between OPS, IAE, MES, Performance, Maintenance (MNT), Management, and Safety Review Group personnel, to discuss the findings from L
troubleshooting the SSPS and VC chiller problems assc ulated with the Unusual Event.
.5.
CONCLUSION-L This event is assigned a cause of Equipment Failure because j
- a circuit board in Train B SSPS failed.
When the I
demultiplexer circuit board failed, erroneous signals were
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DPC/MNS INPLANT hEVIEW No. 92-06 PAGE 7 of 32 processed by the downstream portion of the SSPS.
Subsequently, orratic and erroneous signals woro sont to output devices (annunc.iators) connected to the SSPS.
- After initial investigation, MES personnel do not think that the circuit board Ialled solely due t.o a higher than normal temperature in the CR.
MES personnel stated the olovated CR temperature may.have contributed to an accolorated failuro of the circuit board but was not the primary failuro initiator.
They attempted to reproduce the operating conditions of the fallod circuit board by utilizing a heat gun, however,=the results of this test were inconclusivo.
MES personnel believe the failure was either random or the circuit board was near the cnd of its service lifo.
The particular circuit board had been in service since initial operation.of the SSPS.
Similar components have a history of high reliability, however the Nuclear Plant Reliability Data System does not track this individual component.
Prior to this ovent, McGuire Nuclear Station (MNS) had never had another circuit board of this type fail.
The circuit board failure was isolated by IAE and MES-personnel to 1 bad
. integrated circuit (IC) chip on the circuit board.
The defective IC chJp contains a clock-circuit which runs continuously.
Tho-other circuit boards in the SSPS do not run continuously and,-therefore, chould' experience a much longer'servico. life.
Therefore, MES personnel have E
dotermined that additional SSPS circuit boards are not required to be changed out as a result of this event.
MES personnel havo contacted Westinghouse and other industry personnel about the possible failure mechanisms of the defectivo' circuit board. -The failed circuit board has been removed from the McGuiro inventory of spare SSPS parts, t,t-l :--
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DPC/MNS INPLANT REVIEW No. 92-06 PAGE 8 of 12 This event is also assigned a chuse of Defective Procedure due to the change required to procedure IP/0/A/3010/07 before troubleshooting and repair activities could be completed on Train B SSPS.
The necessity to perform a procedure change delayed recovery efforts and contributed to an extended time Train B SSPS was inoperable.
Had Train B SSPS been returned to operable status prior to initiating a load reduction, ah Unusual Event would not have been required to be declared.
MES personnel concluded that the SSPS problem was not solely temperature related.
Therefore, the circumstances regarding the CR VC chiller did not contribute significantly to the event, however, at the tiae, it was believed by OPS CR personnel that thu olevated temperature in the CR was the primary cause of the spurious annunciator alarms and Train B SSPS failure.
OPS CR personnel were aware that elevated temperatures in the CR have contrJbuted to erratic electronic equipment performance in the past and took action to restore cooling to the CR.
As a result of previous difficulties with the VC system, it is norma) operating practice for HVAC crew personnel to be
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on stand.y whenever a U #c chiller is scheduled to be swapped.
As soon as CR VC Chiller B tripped, HVAC cre.1 personnel immediately started troubleshooting and attempted to restore a source of cooling to the CR.
Neither CR VC Chiller A or B could be restarted immediately because the chiller control circuitry contsins a timer which prevents restarts until 15 minutes have elapsed.
This feature is pravided to allow adequate time for heat dissipation from the chiller motor due to high starting currents, thus preventing chiller motor da;;. age.
CR VC Chiller A was
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DPC/MNS INPLANT REVIEW No. 92-06 PAGE 9 of 12 restarted to return the VC system to operation while repairs were implemented on CR VC Chiller B.
IIVAC crew personnel found a loose flare nut fitting on the oil recirculation line installed by NSM MG-52125.
The fitting was tightened, freon was added to the system, and the repaired component was checked to ensure no additional leaks were present.
This event is aJso assigned a cause of Management Deficiency
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due to insufficient written instructions.
At the time of the event, there was inadequate procedural guidance in place to direct. OPS CR personnel to consider application of screening criteria for declaring an Unusual Event.
The l
information needed-for this decision is included in procedure RP/0/A/5700/00, however, procedure RP/0/A/5700/00
- was not initially referenced and declaration of an Unusual Event was not initially considered by OPS CR personnel at the appropriate time.
The Unusual Event was declared after plant conditions were discussed with licensed OPS management personnel.
The PIR documenting the event stated that OPS personnel did not make the required state and county notifications within the 15 minute. time requirement as stated in procedure RP/0/A/5700/01.
This notification occurred at 1127 which is 17 minutes after the documented Unusual Event declaration L
time of 1110.
The exact time the Unustal Event was declared could not be-determined during the event investigation.
When questioned during the event investigation, OPS Management personnel. involved in the event stated that the Unusual-Event was declared at 1115.
However, the OPS person
- completing the required Unusual Event Notification documentation stated he was unsure of the exact time the Unusual Event was declared and conservatively wrote the l
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-INPLANT REVIEW No. 92-06 PAGE 10 of 12 Unusual Event declaration time as 1110.
Corrective _ Actions 1 Immediate:
An Unusual Event was declared.
Stibsequent:
1.
VC system operability was re-established by restarting CH VC Chiller A.
2.
The loose flare nut fitting on CR VC l
Chiller B was tightenod, froon was added to the system, and the repaired i
component was checked to ensure no l
additional leaks were present.
3.
MES and IAE personnel performed an investigation to determine what caused the spurious CR annunciator alarms.
4.
Procedure IP/0/A/3010/07 was revised to permit continued troubleshooting and repair of the SSPS.
5.
The failed Train B SSPS circuit board
,was replaced.
6.
MES personnel discussed possible tallure mechanisms of the defective circuit board with Westinghouse and other industry personnel.
7.
OPS CR personnel referred te procedure i
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8.
OPS CR personnel made the appropriato notifications to NRC, state, and county organizations.
9.
MES and OPS personnel evaluated change out of all SSPS clock counter circuit boards. It was subsequently decided that-these components should not be replaced at this time.
l-Planned:
OPS personnel will ovaluate' appropriate i
controlling procedures for unit operation and load reduction und add. steps to these procedures for CR personnel to refer to procedure RP/0/A/5700/00 requirements it other than a normal load reduction or shutdown is initiated.
Sa'foty:Analysisg The spurious annunciator alarms were caused by a failed I
-circuit card in the Train B SSPS.
Train A SSPS' remained.
operable during-the event and was capable of providing the required fur.ctD na of the SSPS.
Once Train B SSPS output was disabled, e 1. spurious annunciator alarms in the CR clearen
-During the event when both trains of the VC system were not Lin operation,. OPS CR personnel-referred to the CR high
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DPC/MNS INPLANT REVIEW No, 92-06 PAGE 12 of 12 temperature procedure which ensured CR temperature did not exceed 120 degrees F as specified _n TS 3/4.7.6.
During the i
event, the temperature did not exceed approximately 79 degrees F.
During the event, there were no events that would have
. required operation of the VC system to maintain the habitability of the CR.
No other plant safety systems were required to, and did not operate, as a result of this event.
There were no personnel injuries, radiation overexposures, or. releases of rauloactive material as a result of this event.
The health and safety of the public were not affected by this event.
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