ML19332B971

LER 89-018-00:on 891017,inadvertent Plant Protection Sys Actuation Occurred When 120 Volt Ac Vital Electrical Distribution Panel Breaker Opened.Caused by Personnel Error. Personnel Reinstructed on Removal of channel.W/891116 Ltr

ML19332B971
Person / Time
Site:	Arkansas Nuclear
Issue date:	11/16/1989
From:	Ewing E, Millar D ARKANSAS POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
2CAN118904, LER-89-018-01, LER-89-18-1, NUDOCS 8911220133
Download: ML19332B971 (5)

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Correspondence i I

November 16, 1989

, l 2CAN118954 U. S. Nuclear Regulatory Comitission Document Control Desk F Mail Station P1-137 I Washington, D.-C. 20555

SUBJECT:

Arkansas Nuclear One - Unit 2 Docket No. 50-368 License No. NPF-6 Licensee Event Report No. 50-368/89-018-00 I

Gentlemen:

In accordance with 10CFR50.73(a)(2)(iv), attacheo is the subject report concerning a personnel error allowing maintenance activities in two Plant Protection System channels simultaneously which resulted in an unexpected automatic actuation of the Plant Protection System.

Very truly yours.

E. C. Ewing General Manager.

Technical Support and Assessment ECE/0M/sgw

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Form 10f.2. cia

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, (9 83) Approved OMB No. 31b0 0104 -

Empires: 8/31/$b LICEN5Lt tVENT RtPOR1 (L E R) i l FACILITY hAME (1) Arkansas Nuclear One, Unit Two 100CAET NVMB(R (2) IPhD (3) 10151010101 31 61 Bl110Fl014 YTTLE (4) Personnel Error A110 wing Maintenance Activities in Two Plant Protection System Channels

$1multaneously Resulted in an unexpected Automatic Actuation of the Plant Protection System .

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tillN5f( CONTACT FOR THIS LER (12)

Name l Telephone Number IArea l Dana Miller, Nuclear Safety and Licensing Specialist ICode I 1610111916141 13111019  :

COMPLif t DNf L1ht FOR E ACH COMPONENT F AltpRf DESCRIBED IN THIS kiPoki (13) '

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On October 17, 1989, an inadvertent Plant Protection System (PPS) actuation occurred when a 120 VAC vital electrical distribution panel breaker was opened. The system had been partially oeenergired prior to this occurrence due to an unrelated maintenance activity on a pressuriser pressure variable '

setpoint card. A reactor trip signal occurred and a Main Steam Isolation Signal (M515) were generated I as a result of the PP5 actuation. Upon reclosing of the breaker, Safety injection, Containment Cooling, Containment Isolation and Containment Spray Actuation Signals were generated. Since the plant was in a '

re'ueling outage, with the fuel assemblies stored in the Spent Fuel Pool, at the time of occurrence of this event, a limited amount of Engineered Safety Features ([5F) was aligns.1 for automatic actuation. ,

Nowever, those components which were inservice actuated as oesigned. When the breaker was opened, 5 team Generator pressure instrumentation failed low resulting in the M515 and when the breaker was reclosed, Containment Building pressure instrumentation spiked causing the other E5F actuations. The PPS channel which was Oeenergized was returned to service and the 15F actuation signals were cleared.

The root cause was personnel error, in that maintenance activities were allowed to be performed in two PP5 channels simultaneously. This event is reportable pursuant to 10CFRb0.73(a)(2)(iv).

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Foren 1002.010 -

NRC F. ore 366A U.S. Nuclear Regulatory Commission o *(9 83)- Approved OMB No. 31b0 0104 i

[xpires: 8/31/65 LIC(N5([ [vtNT REPORT (LlR) T[KT CONTINUATION FACILITV NANC (1) lDOCsL1 NU4l'!R (2) l tlk NLB4B(k (6) l PAG [ (3) l l l l$equentiell l Revision l Arkanse6 Nuclear One, Utitt Two l l Yearl l Mumber i Number l  !

10151010101 31 61 61 M 91 I 01 Il el - 01 Ol0lF10F igy TE AT (If more space is required, use auditions) NRC iorm 366A's) (17)

A. Plant Status At the time of occurrence of this event. Arkansas Nuclear One, Unit Two (AND 7) was defueled.

A11 the fuel assemblies were stored in the spent fuel pool. The reactor had been shutdown since the beginning of the seventh refueling outage (!R7) on September 25, 1989. The reactor vessel was defueled on October 16, 1989. ,

B. Event Description The Reactor Protective System (RPS) [JC) and the Engineered Safety Features Actuation System (ESFAS)

[Ji] are subsystems of the Plant Protective System (PPS) and consist of sensors, initiating it.gic and actuation logic circuits which monitor selected plant parameters and generate a reactor trip signal and automatic actuation signals to components in the Engineered Safety Features (t$F) systems if these parameters reach preselected setpoints. The reactor trip signal is used primarily to open reactor trip circuit breakers, interrupting power to the control element assemblies (CIAs), i.e. , control rods, which f all into the core if withdrawn, ensuring the reactor is shut down. Thc Core Protection Calculators (CPCs), a subsystem of the RPS, supply a reactor trip signal for low Departurs from Nucleate Boiling Ratio (DNBR) and high Local Power Density (LPD) to each RPS channel. The ESF actuation signals are used to automatically actuate systems / equipment t

needed to mitigate the consequences of design basis events.

The fo16owing actuation signals are generated by the (5 RAS.

1. Containetnt Isolation Actuation Signal (CIAS)

2. Conteinment Spray Actuation Signal (CSAS)

3. Containment Cooling Actuation Signal (CCAS)

4. Main Steam Isolation Signal (M515)

6. Safety Injection Actuation Signal (51AS) >

6. Recirculation Actuation Signal (RAS) '

7. (mergency Feedwater Actuation Signal (IFAS)

Four independent measurement channels (A, 8. C and D) are provided and designed such that a two out of four coincidence of like initiating trip signals is required to generate a reactor trip Or actuate an E5F system. Each channel is separated f rom other channels to provide physical and electricai isolation of the 61gna16 to the system initiating logic. Each channel is also supplied electrical power from a separate Class II, 120 VAC vital electrical distribution panel (2RS 1 through 2R5 4). The system is designed so that a loss of power to the measurement channels ,

and/or to the logic systems will cause system actuation, i.e., fail safe. For example, a loss of  !

power f rom vital power panel TRS 1 will cause system components in channel "A* to deenergire and '

results in what is termed a

• half leg" trip. This produces essentially half of the logic necessary for generation of a reactor trip signal and all ($F actuation signals, however, no component sctuation (no (SF signal generation) should occur as a result of this condition alone. With the system in this condition, a failure or loss of power tu other system components (power supplies, relays, bistables, etc.), or the presence of an initiating signal of some type in channels. *B." '

"C." or *0" could produce a reactor trip signal and/or tsF actuation signal (s) and satisfy the other half of the trip logic. The type of signals generated are dependent upon the specific component failure or the type of initiating signal pre 6ent. Several different failure modes are j possible which could cause the generation of one or more actuation signals, t On October 17, 1989, the 'D' channel of PP5 was deenergized to perform maintenance on a pressurtrer pressure variable setpoint card. The channel was not bypassed and a half leg trip of the PPS was generated as expected by the Control Room Operations personnel. A plant modification was also in progress to replace the existing CPCs with new CPCs. The modification required wiring changes in the 1PD VAC vital electrical distribution panel to connect the new CPCs to electrical power. On October 17,1989, at 0928 hours0.0107 days <br />0.258 hours <br />0.00153 weeks <br />3.53104e-4 months <br />, to support the required wiring changes, a breater (2RS217) in the 120 VAC vital electrical distribution panel which supplies 'B' channel CPC and PP5 was opened, which resulted in an unexpected M515 and reheter trip signal on channel 'B' of the [5FAS. With a half *1eg trip already generated by channel 'O' being deenergited, a reactor trip and an [$F actuation occurred. Instrumentation signals from a 5 team Generator pressure transmitter failed low when the breaker was opened resulting in the MSIS. Upon receipt of the M515, the Auxiliary Cooling Water (ACW) system (KG) header isolation valves and the service water System (SWS) [BI) inlet supply valves to the Spent Fuel Pool Heat Exchanger and the Component Cooling Water Heat

g-O Form 1062.01B l * ,WRC Form 366*, U.$. Nuclear Regulatory Commiction >

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Arkansas Nuclear One, tinit Two l l Yearl i Number i i Number l 10151010101 31 61 BI el 91--I of 11 el- I 01 Ol013l0Fl0l4 TLA1 (if aiore space is required, use accitional NfW: Form 360A's) (17) l

[xchangers closed as designed. To recover from the MSIS trip, breaker 2R52 17 was reclosed at which time an 51 A5, CIAS, CCA5 and CSA5 were unexpectedly received on channel 'B'. Again unexpectedly an ($F/RPS actuation occurred upon achieving the two out-of four trip logic. When the breaker was closed, a Containment Building pressure instrument momentarily spiked high above the tMp setpoints for SI AS, CI AS, CCA5 and CSAS. As a result of the 51AS, a standby Emergency Diesel Generator (IDG) ((K) started automatically as designed. Other E5F equipment that was available for autosiatic ,

operation, i.e. , not tagged out for maintenance or otherwise locked out, actuated as designed. ,

There were no adverse consequences as a result of the equipment actuations. Control Room Operations personnel took the appropriate steps to recover from the t&F actuations and restored power to 'D' PPS channel to reset trip paths and actuation signals.

C. Safety significance The unit was in a defueled condition, therefore, no components were actuated as a result of the  ;

reactor trip signal generated ty RPS.

To supply emergency power to L5F equipment electrical busses, only one EDG was required to be aligned for automatic operation prior to this event. The standby EDG started automatically as y desioned upon receipt of an $1AS. However, normal offsite power to the [$F buses was maintained [

throughout the event, therefore, the (DG was not required to supply emergency power. The unit operated in a running standby condition for approximately one hour, then was secured.

AP&L administratively controls the position of certain ESF actuated components while the phnt is in shutdown modes to minimize the consequences of inadvertent automatic actuation of the ESFAS.

For example, the control handswitches for the high pressure safety injection pungs and containment building spray pumps are maintained in a

• pull to-lock" position so that the pumps can not automatically start. These components / systems are not required to be capable of automatic operation when the  ;

plant is in these modes and it is recognized that the probability of inadvertent actuations is +

higher during conditions when systems are in abnormal configurations while maintenance activities f are being performed. Therefore, as a result of the inadvertent PPS actuation, a minimum amount of equipment was actuated. .

Considering the plant condition existing at the time of this event and the fact there were no I adverse consequences resulting from the inadvertent actuation of the ESF equipment, there was no i safety significance as a result of this event.  !

D. Root Cause i t

The root cause of the E5F/RPS actuation was determined to be personnel error. The Operations Shift Supervisor allowed maintenance activities to be performed in two PPS channels simultaneously.

Although, the work associated with 'B' channel CPC was alone not expected to result in a condition which would cause an [$F actuation, precautions should have been taken since breakers in the 120 VAC electrical distribution panel for 'B' channel PP5 were being opened and closed while PPS channel 'D' was already in the tripped condition.

E. Basis for Reportability [

This event is reportable pursuant to 10CFR$0.73(a)(2)(iv), automatic actuation of an E5F/RP5 The event was also reported pursuant to 10CFR50.72(b)(2)(11) as a non emergency event.  ;

I F. Corrective Actions Control Room personnel were instructed to not allow maintenance to be performed in two PPS channels simultaneously. During power operations the breakers in the 120 VAC electrical distribution  ;

panels (2RS 1 through 2RS 4) are not opened, therefore, this condition would not occur during power operations. No changes to the electrical system are planned as a result of this event.

t Operations Management discussed with each operating crew the removal of more than one channel of PPS simultaneously. Additionally, it was emphalited that work activities should be paced such that safe operations are maintained. Pre-startup meetings are being held by Operations Management reviewing previous operational events to increase overall performance and awareness of plant operations.

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s. O l t- i Form 1062.010

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Arkansas Nuclear One, Unit Two l 1.Yearl I humber I Number l l 10l$1010101 Si 61 81 el 91--I 01 11 ti - 01 Ol01410Fl014 i TEKT (If more spece is required, use additional NRC Form 3664's) (17) .

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Arkansas Power and Light Company (AP&l) recognizes the need to further evaluate peneric 'j implications related to this and previous events and intends to incorporate the results of the j t'

a; evaluation in AP&L's response to the Diagnostic Evaluation.  ;

G. Additional Inforsetion  !

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.. There are no previous similar events resulting in E5F/RPS actuations caused by maintenance activities  !

being performed in two PP5 channels simultaneously.

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