ML19325E661

LER 89-035-00:on 890930,reactor Automatically Scrammed During Performance of Routine Reactor Protection Sys.Caused by Defective Test Switch in Reactor Protection Sys.Test Switch Replaced Via Prompt Maint Work order.W/891027 Ltr

ML19325E661
Person / Time
Site:	River Bend
Issue date:	10/27/1989
From:	Booker J, England L GULF STATES UTILITIES CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-035, LER-89-35, RBG-31700, NUDOCS 8911080205
Download: ML19325E661 (5)

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?h GULF STATES UTELETIES COMPANY

! nwtw uo smon con eina nox m n enuemu tovis.. auns Aid A CODL EN E36 tiOA4 346 BEM 4 October 27, 1989 RBG- 31700 File Nos. G9.5, G9.25.1.3 i

u U.S. Nuclear Regulatory Commission L . Document Control Desk Washington, D.C.- 20555 Gentlemen:-

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River' Bend' Station - Unit 1

' Docket No. 50-458 h Please find enclosed Licensee Event Report No.89-035 for River Bend StationL- Unit"1. This report is being submitted pursuant to 10CFR50.73.

Sincerely, (f.0Mk U. E. Booker Manager-River Bend Oversight

, River Bend Nuclear Group k/)

i- JEB/TFP/RGW/JHM/DEH/ch cc U.S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 1000 Arlington, TX 76011 )

i NRC. Resident Inspector 1 P.O. Box 1051  ;

St. Francisville, LA 70775  :

INPO Records Center 1100 Circle 75 Parkway Atlanta, GA 30339-3064 H  ;

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1 At 0340 on 9/30/89 with the unit at 78 percent power (Operational Condition 1), the reactor automatically scrammed during the I performance of a routine reactor protection system (RPS) - main steam line isolation valve closure monthly surveillance test. The cause of the scram was determined to be a defective test switch in the reactor protection system. The defective General Electric switch (model CR 2940) had inadvertently placed the system in a conservative state i allowing a scram to occur after a half scram signal was initiated as required by the surveillance test.

The test switch was replaced via a prompt maintenance work order.

Prior to successfully completing the surveillance test, the procedure was revised to require verification of proper switch position prior to performing the surveillance and upon restoration. The RPS system was returned to service.

The RPS System actuated per design in response to the defective test switch condition and the reactor scram placed the unit in a safe shutdown condition. There was no adverse impact on the safe operation of the plant nor to the health and safety of the public as a result of this event.

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LICENSEE EVENT REPORT (LER) TEXT CONTINUATION **aovto o.s no mo-om ExPinil 8 31 et pacepfy seanet ene Dates 1 av.eln tai tin uunsethto F*04 @

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RIVER BNND STATION 0 l6 l0 l0 l0 l4 l5 E 819 -

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0 10 Ol2 0F 0 l4 N E M TEY CI N TYO U At 0340 on 9/30/89 with the unit at 78 percent power (Operational Condition 1), the reactor (*RCT*) automatically scrammed during the performance of a routine reactor protection system (RPS) (*JE*) main steam line isolation valve closure monthly surveillance test. The cause of the scram was determined to be a defective test switch (*33*)

in the reactor protection system control logic. This actuation of an engineered safety system is bieng reported pursuant 10CPR50. 73 (a) (2) (iv) .

INVESTIGATION An investigation into the cause of the event disclosed that the unexpected scram occurred when the main steam line 'C' inboard main steam isolation valve (MSIV) (*ISV*) test push button (B21H-S3K) was depressed as directed by the monthly surveillance test procedure which was in progress. The performance of the procedure step should have resulted in only a half scram signal being received by the RPS trip channel 'C'. A review of the emergency response information system (ERIS) (*IQ*) scram data revealed the scram occurred from a trip signal being received on RPS channel 'D' immediately after initiating the trip on RPS channel 'C'.

A review of the RPS system elementary wiring drawings showed that testing the RPS mai.1 steam line isolation valve 'C' channel also ,

causes relay (*94*) contacts C71-K3H in the 'D' trip channel to open.  !

The opening of the C71-K3H contacts is net expected to result in a  !

trip condition of the 'D' Channel because the contacts are bypassed j when test switch C71-S60 is in the normal position.

Test switch C71-S6D is a General Electric Type CR 2940, Part No.  !

145C3040P022, key operated control switch. A visual inspection of the l switch found the key slot of the operator indicating normal (mid) l position. When in the normal position, contacts 3 and 4 are designed l to be maintained in the closed position. A volt meter was used to l '

verify the position of the switch contacts; the actual switch state was found to have contacts 3 and 4 open. Immediately upon discovering the defective switch, a prompt maintenance work order was initiated to replace the switch.

The last previously documented successful operation of the defective  ;

switch (C71-S6D) was on 9/2/89 during the last performance of the RPS i main steam line isolation valve closure monthly surveillance test. 0 Data history from the plant process computer confirmed that the switch failure occurred on 9/2/89 during the restoration of the previous  !

monthly surveillance test. No known indication was readily available i, to the operator identifying that the switch contacts failed to close when returning the switch to the normal position and removing the key, and the procedure did not point out where the information was available. The defective switch permitted contacts 3 and 4 to remain g,o.m. .u.o,o,...o.u J.

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UCENSEE EVENT REPORT (LkR) TEXT CONTINUATION **aovio ove s.o mo-om t ex,ines a n e pastLITV sneast He Docati seveIDen it' tem ssubspen les PA06 tai f

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" @ II"*aTfoTI D P U Eh channel 'D' to be left in a conservative state.

' There have been no earlier LERs submitted by River Bend Station that involved a similar control switch. The root cause appears to be unique to the General Electric key operated control switch.

CORRRCTIVE ACTION Immediately upon discovering the defective switch, a prompt maintenance

! work order was initiated to replace'the switch. In addition to replacing the switch, the RPS main steam line isolation valve monthly

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surveillance test procedure was revised to include instructions for ,

verifying that the RPS test switches are in the proper position prior to performing the surveillance and during the procedure restoration.

The RPS system was returned to service following the replacement of the switch and the successful performance of the revised surveillance test procedure; As a result of a similar failure occurring during the bench testing of a replacement switch, a total of twenty three (23) spare switches of the same part number were obtained from the warehouse and bench tested.

Tests conducted by Engineering found that the switch was capable of failing such that the key may be removed prior to contacts 3 and 4 l

making up in the normal position. Eight failures of this type were

, identified from the twenty-three (23) switches tested. Two switches I

• identified as being defective have been sent to General Electric for i failure analysis. GSU is also performing an independent failure analysis on the defective switches. GSU reported this defect to the NRC pursuant to the requirements of 10CFR21.21 (b) (2) in a GSU letter i dated 10/20/89 (reference RBG-31655), j i After discovering the common failure mode of the switch, a review was l performed to identify other plant applications which utilize switches of this type. River Bend has confirmed that there are twenty four (24) safety-related control switches having Part No. 145C3040P22 that havb been installed in plant applications, e.g., as internal components in the reactor protection system and automatic depressurization system.

Engineering has verified that contacts 3 and 4 on each of the installed switches are properly made up for their intended applications.

A review was performed to identify the activities that require operation of the subject control switches. With exception of surveillance test procedure (STP) -051-0 201, "RPS - Main Steam Line Isolation Valve Closure Monthly CHFUNCT" and STP-202-0602, " ADS Safety Relief Valve Operability Test", Engineering has determined that other applicable procedures contain sufficient instructions for verifying proper positioning of the switch contacts. STP-051-0201 has oeen revised to include additional instructions for verifying proper switch positioning prior to performance and during restoration and

-STp-202-0602 will be revised prior to the next scheduled performance.

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IsAC Poem 384 U 8 EUC4 EAR 8.t!ULATEV COMedlESIO8e LICENSEE EVENT REPORT ILERI TEXT CONTINUATION AP aovio ove ao mo-om (xPing1. 6 31'N 9 ACl447V 0540118 44 DOCatiesuettR QI LOR esuhdSSR 166 Pa06 (31 vtan segsjg. e.a6 pyeYo* a RIVER BEND STATION o [s lo l D l 0 l 4l5 l8 8l 9 -

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0l0 0l 4 0F 0l4 vertgggggwmaamm The failure of the switch in the RPS placed the system in a l conservative state. The RPS system actuated per design in response to  :

the defective test switch condition and tha reactor scram placed the '

unit in a safe shutdown condition, As a result, there was no adverse impact on the safe operation of the plant nor to the health and safety of the public as a result of this event, ,

l NOTE: Energy Industry Identification System Codes are identified i

in the text as (*XX*).

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