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While in Cold Shutdown on October 3, 1986, during Instrument & Controlinvestigation of abnormal indication on panel 1125f0 for Occay ticat System(0l15) "0" Room sump stack lights, SFAS "B" bistables tripped causing flV-20002to close, which tripped OllS "B" Pump. The plant was without the use of thenormal OllS for approximately 13 minutes. Due to the extended period that theplant has been shutdown, there was a small, but detectable increase of reactorcoolant temperature. Steps were taken immediately to restore a OllS train toservice in accordance with the intent of Technical Specification 3.1.1.5. Thisevent is reportable according to 10 CFR Part 50.73(a)(2)(iv & v).

the cause of the incident was I&C technicians troubleshooting abnormalindication on panel ll2SFB for Oll5 "0" Pump Room (East) Sump stack lights(10 inch Icvel indication) on Panel ll2SFB.

the ininediate cause of the spurious actuation was an electric ara f rom the sumplevel stack light when " rolling-over" the respective bulb. The arc initiatedthe trip of inverter "0".

As a long term corrective action, the DC vital power supplies will be modifiedto be equipped with static transfer switches. those switches, upon detectionof a fault, will very rapidly transfer the vital bus to an alternate power.This transfer will allow the fuses in the bulb circuit to operate and isolatethe fault without affecting the remainder of the DC vital power supplied loads.

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While in Cold Shutdown on October 3, 1986, during Instrument & Controlinvestigation of abnormal indication on panel H2SFB for Decay Heat System(DHS) "B" Room sump stack lights, SFAS "B" bistables tripped causing HV-20002to close, which tripped DHS "B" Pump. The plant was without the use of thenormal DHS for approximately 13 minutes. Due to the extended period that theplant has been shutdown, there was a small, but detectable increase in reactorcoolant temperature. Steps were taken immediately to restore a DHS train toservice in accordance with the intent of Technical Specification 3.1.1.5.This event is reportable according to 10 CFR Part 50.73(a)(2)(iv & v).

The plant was in cold shutdown, using functional DHS "B" Train to provide heatremoval, while the OHS "A" Train was being drained for repairing a leakingpump casing drain line. The plant was in the " action statement" of (non-STS)Technical Specification 3.1.1.5.

At the time of the event, both of the steam generators (OTSG's) were inoperabledue to the RCS piping snubber seal replacement work being performed at thetime, although the manways were installed following 0T50 sleeving activities.However, the primary side upper hand holes were open in order to provide lowtemperature over-pressure protection of the RCS. Casualty Procedure C.12" Loss of Decay Heat Removal System" was in effect during the period to providedecay heat removal, had the system remained out-of-service for an extended

a period.

OHS f low to the RCS was lost at 0947 on October 3,1986 when the "VliAL POWERBUS 10 TROUBLE" alarm (window number 32 on panel H2ES) and its associated"f!HSI 001" red light (window number 16 on H2PSA) was received along with manyother alarms on panels H2ES, H2PS, and H2SfB. It was restored at 1000 thesame day.

The cause of the incident was 1 & C technicians troubleshooting abnormalindication on panel H2SfD for DHS "B" Pump Room (East) Sump stack lights(18 inch level indication) on Panel H2SfB. The incident was readily apparentto the Control Room Operators,

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An operator was instructed to don protective clothing and obtain dosimetry inorder to enter the Reactor Building to manually open HV-20002 if it could notbe reopened from the Control Room. Control Room operators were directed tomonitor incore temperatures. They set up an initial group of incorethermocouple temperatures on the ! DADS computer system (NRC LER System "!D")printer, along with a visual system display print-out. An auxiliary operatorwas directed to inverter "B" and SIB, and since he was in the vicinity, heobserved normal conditions very soon after the trouble started. The ! & C

! technicians checking the DHS "B" pump room sump stack lights were instructedto come to the Control Room. The control room began steps according toCasualty Procedure C.12. " Loss of Decay Heat Removal System." The SFAS "B"analog bistables were noted to all be in the tripped condition. The reset ofHV-20002 at panel 20107 was directed, but did not occur since the contactbuffer was not yet reset. The contact buffer was reset, followed by reset atpanel 28101, resulting in regaining control of HV-20002. Normal flow with theDHS pump was established at 1000 hours. The monitored incore temperatures didnot increase more than one to three degrees-f, depending upon the computerpoint used. The temperatures recorded were initially in the low-to-mid-eighties (in degrees-f).<

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The sump stack lights are indications of the sump DHS Pump rrom sump level inthe Con * el Room. The indicators are a series of Master Specialties (NRCManufacture Code - M128) back-lighted push-buttons which need to be " rolled"after disconnecting them from their socket in order to change the lightbulbs. The part which rolls is spring loaded into its respective socket. Thesump stack lights are related to a circuit which activates and de-activatesthe sump pumps in those rooms.

The District recently revised Casualty Procedure C.12 to reflect current coldshutdown conditions. This procedure uses the gravity head of the Borated WaterStorage Tank (BWST) to provide DHS flow to the RCS. In addition, recentcalculations of existing core decay heat have determined that there is greaterthan six hours time before any core cooling would be necessary to keep thereactor coolant below 200 degrees-f. Therefore, the plant operators hadsufficient time to enter the Reactor Building, manually control HV-20002 andrestart the otherwise functional DHS "0" pump for long term cooling of thecore, or to implement procedure C.12 before any genuine concern for corecooling would exist.

Due to the compensatory measures available, the public's health and safetywere not affccted by this event. The normal long term cooling configurationof the DHS is more crucial during a shutdown, than during power operations. Amore crucial time for this event to have occurred is not likely in that theredundant loop was out-of-service.

The error was associated with an activity or task that was not covered by aprocedure. The type of personnel involved were utility personnel other thanplant operators,

the immediate cause of the spurious actuation was an electric arc from thesump level stack light when " rolling over" the respective back-lightedindicator. Based on experience with these components, the arc could have beendue to an incorrectly sited bulb inserted in the back of the indicator, or abroken spring clip which holds the iqdicator in its socket. The arc initiatedthe trip of inverter "0". The loss of inverter "0" caused numerous alarms tobe logged on the alarm typer by the plant computer. A short circuit caused byan arc from a bulb in a stack of lights for DHS "0" Room sump Icvol indicationcaused a voltage transient on tPo 120 VAC Vital Bus "0", (NRC LER System "[[")which tripped the inverter, tripping SFAS "0" analog bistables, causing DHSdropline isolation valve HV-20002 to close (spurious high (> 255 psig) reactorcoolant system pressure indication) and simultaneously causing a trip of theOHS "0" pump. Inverter "0" reset itself automatically, as designed, duringthis transient, ihr consequences of 1 loss of inverter "0" are minimited bythe presence of inverter "A". Howeve*, the spurious trip of HV-20002 resultedin the normal UHS being taken out-of-service.

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The plant Electrical Group wrote Work Request #119898 to examine the actualcause of the short circuit during the indicator roll-over. This diagnosticwill be performed when a similar failure will have less significantconsequences. The results of that investigation will dictate the requiredcorrective actions with respect to the lighting circuit short. This LER willbe revised, following the completion of that investigation, by July 31, 1987.As a long term corrective action, the DC vital power supplies will be modifiedto be equipped with static transfer switches. Those switches, upon detectionof a fault, will very rapidly transfer the vital bus to an alternate power.This transfer will allow the fuses in the bulb circuit to operate an<* isolatethe fault without affccting the remainder of the DC vital power sup.slied loads.After a fault is detected, the current Auxiliary Building Inverters do notreset fast enough to prevent the SFAS logic from sensing a loss of power onthe vital bus. The work to add the static transfer switches to the vitalbusses will be completed prior to Restart.

The inverter is referred to in the NRC LER System Component list as "INVi".Rancho Seco's SFAS is NRC LER System "JE." The decay heat system (OHS) is theNRC LLR System "0P."

Loss of an inverter. SFAS actuation, and plant trip due to a similar shortcirt. ult was reported previously by LER 70 01 when a light bulb was droppedinto an exposed indicator socket,,

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