ML19332E611
| ML19332E611 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 11/30/1989 |
| From: | Hairston W, Odom R GEORGIA POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| ELV-01113, ELV-1113, LER-87-005, LER-87-5, NUDOCS 8912080068 | |
| Download: ML19332E611 (10) | |
Text
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- ;, ; j Atlanta, Georgia 30308.-
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, Telephone 404 526-3105.-
-' Maihrg Address:
-40 inverness Center Parkway
, , Post Offce Box 1295 - .
- 7. _: Birmingham'. A:abama 35201..
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, ' Telephone 205 868 5581 jtl No'vember 30, 1989. " = ^e""**cSreem
- : W. G. Hairston, lll -
t M*e E-Senior Vce Presdent
, ; - Nuclear Operations
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, s ELV-0111'3 p '- 1 , , ,
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39 . Docket- No. : 50-424 U.: S. Nuclear Regulatory Commission
-r# ' ATTN: Document Control Desk Washington, D. C.-l20555-
' Gentlemen:
V'0GTLE ELECTRIC GENERATING PLANT 1 m LICENSEE EVENT REPORT 120V AC VOLTAGE TRANSIENT CAUSES ESF ACTUATIONS g
i o ,
< LIn accordance with 10 CFR 50.73; Georgia Power Company hereby submits the !
Lenclosed report revision.concerning r.ctuations of ESF-systems.- This revision !
.. jupdates_ the cause and corrective action as a result'of further investigation-T- $followingasimilarevent-;on, November 13,.1988 (Ref. LER 50-424/1988-035-01).
Sincerely, r
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W.~ G. Hairston, Ill
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Enclosure:
- LER 50-424/1987-005-06
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-xc: -Georaia Power' Company j
. Mr.
Mr.jC. K. McCoy ,Jr.
G. Bockhold,- j' Mr.
JMr.'R.'M.-Odom P. D. Rushton M NORMS. -
U. S.-Nuclear Reaulatory Commission cp .Mr. S. D. Ebneter, Regional I.dministrator Mr. J. B. Hopkins, Licensing Project Manager, NRR
.Mr.cJ. F. Rogge,-~ Senior Resident Inspector, Vogtle p2-L t g ;
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.120V:AC VOLTAGE TRANSIENT CAUSES ESF ACTUATIONS EV8NT DATI (S)
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'Since February 23, 1987, Plant Vogtle has experienced six control room ventilation isolation signals from control room outside air duct radiation monitor-1RE-12116. These actuations occurred on February 23 and 27, 1987; March 26 and 30,' 1987; and April 6 and 22, 1987. On March 4, 1987, a Containment
. Isolation Actuation (CIA) and a Containment Ventilation Isolation Actuation (CVI) occurred as a result of spurious signals from high range radiation monitor 1RE-0006_and. low range radiation monitor 1RE-0003. Investigation and testing revealed'that voltage transients are being introduced on the 120V AC vital power r supply whenever the Safety Features Sequencer System (SFSS) is re-energized p after being de-energized for maintenance, testing, etc. This voltage transient sometimes causes the data processing modules (DPM's) in the radiation monitors
., ; to sense a loss of power, thereby initiating a false high radiation signal and causing a control room ventilation isolation.
~
, The.cause-of the . control room ventilation isolations was apparently due to 1
random failures of the DPM, which was replaced. The apparent cause of the L CIA /CVI was a conservative setpoint in an inverter circuit which shuts down E
power to the radiation monitor's OPM whenever a large inrush of current is experienced, such as when the SFSS is re-energized. Plant personnel plan to increase the circuit's setpoint during the next refueling outage.
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'A.- REQUIREMENT FOR REPORT-
-Thisireport is required per 10 CFR 50.73 (a)(2)(1'v) since actuations of the !
control: room ventilation isolation system, ' containment isolation, and the !
containment ventilation isolation as a result of the high radiation signals. >
from the radiation monitors constitute unplanned automatic Engineered Safety '
. Feature (ESF) actuations.;
B.: UNIT STATUS AT TIME OF EVENT
-At.the: time of the February 23, 1987 event, the unit was in Mode 3 (Hot
-Standby) with:a reactor coolant system (RCS). temperature of 400 degrees Fahrenheit and a pressure of 600 psig. Control room outside air intake radiation monitors--1RE-12116 and '1RE-12117 were operable. The control room '
ventilation system was in the normal mode.
- At theltime of the February 27, 1987 event, the unit was heating up in Mode ,
4-. (Hot Shutdown) prior to entry into Mode'.3. Control room outside air intake radiation monitors 1RE-12116 and'1RE-12117 were operable. The control room' ventilation system was in'the emergency mode, undergoing HVAC filter unit testing.
' At the time of the March 4,1987 event, the unit was in Mode 3 (Hot Standby) at 0-percent of rated thermal power (RTP). RCS temperature and pressure were approximatelyz 557-degrees Fahrenheit and 2235 psig..
At the time-of the March 26,'1987 event, the unit was in Mode 1 (Power 10perations) at 12 percent RTP. Control room air intake radiogas monitors 1RE-12116 and 1RE-12117 were operable. The control room ventilation system
- was in the normal mode of operation.
At the time'of the April 5, 1987 event, the unit was in Mode 3 at zero percent RTP. RCS temperature and pressure were 557 degrees Fahrenheit and 2235 psig, respectively.
. At the time of the April 22, 1987 event, the unit was in Mode 1 at 74 I percent RTP. RCS temperature and pressure were approximately 580 degrees .i y ' Fahrenheit and 2235 psig, respectively. Radiation monitor 1RE-12117 was out I of.. service (in' a Limiting Condition of Operation per Technical Specifications) at the time of the event.
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T C. DESCRIPTION 0F EVENT
~At-1954 CST on February 23, 1987, a Control Room Ventilation Isolation (CRI)~
occurred' as;a result of a high radiation signal from instrument -1RE-12116,
- one of the two radiation detectors monitoring' the control room outside air duct. The cards for the- alarms to alert the operators were out of. service
- for testing.- This event was-immediately apparent to the control room !
operators due ,to the monitoring light indications in the control room. I Operations personnel immediately' checked radiation monitor 1RE-12117 (which 1 is11ocated -in the same outside air duct), noted no alarm condition and l'
& - therefore. concluded that monitor 1RE-12116 had malfunctioned. Operations
_ personnel removed 1RE-12116 from service and returned the control room ventilation system to normal configuration. The false high radiation signal 'i y < ; initiated a CRI signal which actuated the control room isolation system. 1 L Emergency supply inlet and outlet dampers opened, both control room filter !
L unit fans started, normal discharge and return air dampers closed, and i E normal control room fans tripped on low flow, as designed. j At 1030 CST, on February 27, 1987, a CRI occurred because of an. isolation l signal generated by radiation monitor 1RE-12116. This was not immediately apparent to the control _ room operators since the control room ventilation ,
system had earlier been placed in the emergency mode for testing. At-1614 CST, a Chemistry Department supervisor notified the main control room '
operations personnel that radiation monitor 1RE-12117 was in an alert alarm state.(approaching setpoint). Operations personnel reviewed equipment i L ~ status data (e.g., sequence of events recorder print-out and plant effluent !
L radiation monitoring' system) and discovered the previous control room 1 L
isolation. Only the control room kitchen, toilet, and conference room fan ;
inlet dampers-(1HV-12162 and 1HV-12163), which are in series, closed because ;
the ventilation system had previously been placed in the emergency mode for HVACl filter unit testing.
[ On March 4, 1987, plant operators were performing startup test #1-588-02,
?
--" Pressurizer Heater and Continuous Spray Flow Verification", and Instrument and Control- (I&C) personnel were changing circuit boards- on the Safety i Features. Sequencer System (SFSS). At 1248 CST the control room received !
spurious signals-from.the containment high range radiation monitor (1RE-0006), which automatically actuated the Containment Isolation (CIA),
and low range radiation monitor (1RE-0003), which automatically actuated the Containment Ventilation Isolation (CVI) system. These systems are s
Engineered Safety Features.(ESF's) of the plant. After verifying that no condition existed which required these actuations, which included checking the redundant high and low range radiation monitors (1RE-0005 and 1RE-0002),
plant operators reset the CIA /CVI signals and began to reopen the affected valves. Startup test 1-5B8-02 was stopped and Engineering Support personnel were called to the control room to assist in determining the cause of the actuation.
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DOCKtT NUMSER m LER NUMBER (61 ~ PAGE(31 Y8^R '
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'l At: 1305, a second CIA /CVI occurred. again, as a result of spurious signals
. generated from radiation monitors 1RE-0006 and IRE-0003. Again, plant O operators verified that no condition existed which required these .
actuations, reset the CIA /CVI . signals and began to reopen the affected -
valves. Work on the SFSS was ~ stopped while Engineering Support, I&C and Operation personnel analyzed these events. Operation's personnel discovered l that the4 undervoltage (UV)- relays energized on the 120 VAC Class IE Power i Panel'(IBY2B)' and that the inverter (IBD1112)'had experienced a voltage drop. Both the; power panel and inverter supply electrical power for
-radiation monitors IRE-0006 and IRE-0003.
~
The discovery indicated that if an UV condition'had occurred, it would have f u ide-energized-the data processing module (DPM) for these radiation monitors and. allowed a logic signal to be generated for CIA /CVI actuations. This was
'later confirmed by allowing-the "B" train sequencer to be re-energized while -
monitoring-the DPM cf 1RE-0006. It showed that this 'JV condition precipitates a CIA /CVI, as expected. Although startup test #1-5BB-02 was i temporarily stopped during these-events, it neither contributed to nor was ,
! ~a ffected by them.
IT On March 26, 1987 at 1341 CST a CRI automatically occurred. The operator checked -the Safety Related Display Console (SRDC) for an alarm condition of H the control room air intake monitors,1RE-12116 and IRE-12117. No alert or high-radiation alarm existed on either monitor, but a trouble light was indicated-on the SRDC for monitor 1RE-12116. Monitor 1RE-12117 indicated normal,.while monitor 1RE-12116 was reading default values. Default values are permanent inserted values inputted whenever there is a loss or
- interruption of power to the DPM. Since monitor 1RE-12117 was indicating l normal, and since there was a trouble light but no alarms on monitor
.1RE-12116, it was concluded a problem with the power supply to the DPM for L monitor 1RE-12116 had caused the CRI. Monitor 1RE-12116 was removed from service and the. control room ventilation was returned to normal ventilation l at.approximately 1350 CST on 3/26/87. Plant systems functioned as designed to-' isolate the control room.
'On March 30, 1987, at 0045 CST, a CRI occurred. The operator checked the
- SRDC for'an alarm condition of the control room air intake monitors, IRE-12116 and 1RE-12117. No alert or high radiation alarm existed on either monitor, but a _ trouble light was indicated on the SRDC for monitor '
1RE-12116, which had failed downscale. Monitor 1RE-12117 indicated normal, while monitor 1RE-12116 was reading default values. Since monitor 1RE-12117 ,
~
was indicating normal, and since there was a trouble light but no alarms on monitor 1RE-12116, it was concluded that a problem with the power supply to the~DPM for monitor 1RE-12116 had caused the CRI. Monitor 1RE-12116 was removed from service and the control room ventilation was returned to normal ventilation at approximately 0435 CST on 3/30/87. Plant systems functioned as designed to isolate the control room.
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0l 6 0 l5 oF 0 l9 j mrw n uM.*.o .a - acr..manmn On April- 6,-1987- at 0122'CDT, a CRI occurred. A trouble light was indicated 0; :on the SRDC:for 1RE-12116. Before the control room operators could 3 determine the cause of the trouble light,- a CRI occurred. The' operator l
- checked the SRDC for' an alarm condition of the control room air intake ;
monitors,i1RE-12116. and ~ 1RE-12117. No alert or high radiation alarm existed . ~t on.either monitor. The-shift supervisor (SS) attempted to reset the CRI signal. The initial reset attempt was unsuccessful; however, at approximately 0129 on April 6, 1987,- the control room ventilation was 1 returned to normal. Prior to this event, a recorder had been installed to measure any. voltage transients to the DPM's. The recorder installed prior toLthe: event indicated that no change in voltage had occurred.
. J0n'Aprik22, 1987, at 1907 CDT, a CRI occurred. The operator checked the SRDC for an alarm condition of the control room air intake monitor,
-1RE-12116. No alert-or high radiation alarm existed, but a trouble light n was' indicated on the SRDC. Monitor 1RE-12116'was reading default values l: while 1RE-12117 was out of service. Since an input voltage recorder showed no abnormalities, and because there was a trouble light but no alarms on
< monitor.1RE-12116, it was concluded that an internal problem with the power l supply in the DPM for monitor 1RE-12116 had caused the CRI. Monitor
" 1RE-12116 was removed from service and the control room emergency
~
- ventilation remainedLin service. . Plant systems functioned as designed to isolate .the control-room and to start the control room emergency HVAC.
D. ~CAUSE.0F EVENT
'Immediate Cause:
Control building control room outside air intake radiation monitor 1RE-12116 apparently sensed.a voltage transient, causing a false high radiation signal
- to= actuate the CRI logic. Additionally, the containment high range
_(1RE-0006) and containment low range (1RE-0003) radiation monitor DPM's sensed an undervoltage condition and both monitors generated a high radiation signal to actuate the CIA /CVI logic.
Root Cause:
o Initially, the apparent root cause of these events was that whenever the
< SFSS_was re-energized after maintenance, surveillance testing, or troubleshooting, a voltage transient occurred on the 120V AC distribution panel. The voltage transient sometimes caused the DPM's for the radiation a monitors to sense a loss of power which in turn may cause a false high
-radiation signal to be transmitted to the Engineered Safety Features Actuation System logic. Further investigation and testing was planned to verify that the voltage transient was causing the control room isolations.
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is However during the-April 6 and 22, 1987 events, involving 1RE-12116 only, a
, - voltage recorder was installed- to_ measure vol' age transients. Since the recorder did not indicate a change in the voltage to the radiation monitor, it now appears that IRE-12116 may have had an-internal defect which would l
..have caused the3 trip of this monitor in this and previously reported events. ;
lThe 120V AC panel voltage ~ transients are still the apparent cause of the failures of.lRE-0003-and IRE-0006. 'Both-the sequencer and radiation monitors _ receive power from the same distribution panel, IBY2B, which is, in
- turn, powered from inverter. 1801112. While it cannot be definitively ascertained,s because the. inverter which supplies IBY2B can not be taken out ,
'of service while the unit 11s in Modes-1, 2, 3-or 4, it is possible that the-
" zip"-circuit'in the inverter shut down the inverter when the sequencer was L < reenergized,;resulting in the loss of power to IBY2B. The zip circuit is b . internal' overcurrent protection in the 1BD1112 inverter. -This protection circuit is activated on overcurrent and on the rate of change of current.
'After this circuit shuts down-the inverter, the inverter is brought up by ramping tt.a inverter output from zero to full voltage. The sequencer load o- .is a capacitive load which may draw a large inrush of current depending on !
l
- what point, fin the voltage cycle, the breaker is closed.
E. ANALYSIS OF. EVENT
' These events were- considered reportable per 10 CFR 50.73 (a)(2)(iv) because the signals from the radiation monitors resulted in unplanned automatic H -actuations'of ESF equipment.
' During the February 23, 1987 event, the Unit was in Mode 3 (Hot Standby) and had not yet achieved initial criticality. Redundant radiation monitor ,
1RE-12117 was -in operation at the time of the event, had not alarmed, and no i f reasonable explanation for the high radiation signal from 1RE-12116 existed. l L _ Since the cause was determined to be a false high radiation signal, and all safety systems responded as designed, no safety hazard was created and the health and safety of the public'was not affected and would not have been affected at higher power levels.
During the February 27, 1987 event, the Unit was in Mode 4 (Hot Shutdown) and still had not yet achieved initial criticality. The control room ventilation system was already in emergency mode to support HVAC filter unit '
testing. Redundant radiation monitor 1RE-12117 had not alarmed, and no reasonable explanation existed for the high radiation signal from radiation l
. ' monitor 1RE-12116. Plant operators concluded that radiation monitor 1RE-12116 had again malfunctioned. Since the cause was also determined to be a false high radiation signal, no safety hazard was created and the health and safety of the public was not affected and would not have been affected at higher power levels.
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- During:the event of March 4,1987, Unit I was in Mode 3 (Hot Standby) and-
.had not yet achieved initial criticality. Redundant radiation monitors 1RE-0003 (low range) and 1RE-0005 (high range), in~ operation at the time of the< event, did not alarm, norL did either monitor display abnormal readings.
1 Therefore, no reasonable explanation existed for the high radiation signal '
, from high range monitor 1RE-0006 or the high radiation signal from low range ,
monitor 1RE-0003.- Since the cause has been determined to be spurious high
+ "
radiation signals, and all safety related ventilation systems responded as -.'
designed .no safety hazard was created and the health and safety of the public was not affected and-would not have been affected at higher power !
L levels.
l The redundant' radiation monitor 1RE-12117 in operation during the March 26, j
1987 event, displayed a normal reading and no alarm condition. Monitor n IRE-12116 did'not show a visual high radiation alarm, but a trouble light on the SROC_ indicated a fault. The control room operators determined a valid radiation signal did not exist. _ Since the cause was determined to be a false CRI actuation signal, and since plant safety systems- functioned as designed 11t is concluded that this event had no adverse effect on plant L safety.
L L The redundant radiation monitor 1RE-12117 in operation during the March 30, 1987 event,-displayed a normal reading and no alarm condition._ Monitor 1RE-12116'did not show a ' visual high radiation alarm, but a trouble light on !
.the SRDC indicated a fault. The control room operators determined a valid radiation; signal did not' exist. Since the cause was determined to be a
' false-CRI actuation signal, and since plant. safety systems functioned as designed, it is concluded that this event had no adverse effect on plant safety. . Since this ESF (CRI) functions independently of reactor power, this event:would also. have had no adverse effect on plant safety even at higher power levels.
The redundant radiation monitor 1RE-12117 was-in operation at the time of
- the event' of' April 6,1987 and had not alarmed or showed any increased radiation. Since the radiation monitor 1RE-12116 never exhibited an actual
- ' radiation condition and a false signal initiated the ESF actuation signal, no safety hazard was created and the health and safety of the public was not affected. .
y
-During the event of April 22, 1987, monitor 1RE-12116 did not show a visual high radiation-alarm, but-a trouble light on the SRDC indicated a fault.
' Additionally, the monitor itself displayed low, or default values. The y.; control room operators determined a valid radiation signal did not exist.
Since the cause was determined to be a false CRI actuation signal, and since
- plant safety systems functioned as designed, it is concluded that this event had no adverse effect on plant safety. Since the ESF (CRI) functions independently of reactor power, this event would also have had no adverse effect on plant safety even at higher power levels.
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0 l 0l 5 _. 0;6 0l8 or 0 j9 vanta - A w ,w w r.,,,,,su u nn F. . CORRECTIVE ACTIONS The failed DPM was replaced and returned to the vendor for additional e : testing. =The vendor testing could not establish a failure mode for the DPM.
, After the re)lacement of the DPM, no more . failures of this type have m
coccurred. :T1us, even though-vendor testing could not determine a failure mode, it: can be_ concluded-that-the DPM was the cause of the CRI' events. l
,. Additional. tests.were performed to simulate a voltage drop on the inverters; '
however,-intentional 4 9 rounding of the bus did not duplicate the voltage
~
drop. The incident clearly demonstrated that any type of inverter failure j
'could cause an ESF actuation. Also, the transfer mechanism for the power f
L l supply for the 120V AC: panels to their alternate power supply is a break before make type of transfer. Thus, an intentional transfer to the 1 l
Lalternate. power supply, _without'taking steps to block the ESF actuations,
- - would causesimilar actuations, i lThe corrective a'ction previously identified was to aroceed with the
-installation of static transfer switches for distri)ution panel IBY28.
These switches provide automatic transfer capability to an alternate power L
supply in case of _ inverter failure, ~ The present transfer mechanism requires ,
'_ operator action-for repositioning the distribution panel input breakers and Lis a break'before make type of transfer. Further study of this proposed
' modification-indicates that this may not' resolve this problem due to the short response time required. Raising-the setpoint of the zip circuit
'should help prevent a momentary loss of power to the radiation monitor !'
during the sequencer power up evolution. Current data does not provide l
' positive indication that installation of the static transfer switches would have prevented this event.
'During.the Spring.1990 refueling outage, the setpoint of the zip circuit ,
will be raised to a higher setting. Eighteen month surveillance testing for !
the sequencer will also occur at that time.
\
4 9
'U,0 GPGs 1986-U O-i39 00070 N C FQRM 366A -
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- IUCENSEE EVENT REPORT (LER) TEXT. CONTINUATION ': maovio ous No mo-oior b,g 5lI ,
EXPIRC3: t/31/M . ,
P44ttlTV ffAhlt 01: DOCKET NUMS4R (23 LtR NUMSER (8) - PAGE lat vtan -
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G'i. ADDITIONAL INFORMATION <
I-- g , ., ..
.It Failed $ Components
' DPM manufactured by Westinghouse Electric Corporation s-4; ;Model f#6091D46G01 '
l s s-L2.- Previous Similar- Events' i None.
1~
lg J 3. -' Energy. Industry ~ Identification. System
+ .'
. < : Low Voltage Power System.- Class IE - ED l!L
~
Radiation Monitoring' System -
'IL
- ~
Engineered: Safety Features Actuation System - JE Containment, Isolation Control System --JM
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! NXC 80XM M '- ou,s. cros 1988-520-589,00070 l^_ -_- ~_ ,, ._ -
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