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January 22 , 1992RBG- 36289File Nos. G9.5, G9.25.1.3

U.S. Nuclear Regulatory CommissionDocument Ccntrol DeskWashington, D.C. 20555

Gentlemen:

River Bend Station - Unit 1Docket No. 50-458

Please find enclosed Licensee Event Report No. 91-022 forRiver Bend Station - Unit 1. This report is submittedpursuant 10CFR50.73.

Sincerely,

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W .1 . ellManager - Oversight

['h.[ 1U k, Vf}Y. River Bend Nuclear Group

IJ LE/PDG/ GAB /DCH/ TAR /kvm

cc: U.S. Nuclear Regulatory Commission611 Ryan Plaza Drive, Suite 400Arlington, TX 76011 <

NRC Resident InspectorP.O. Box 1051St. Francisville, LA 70775

INPO Records Center1100 Circle ParkwayAtlanta, GA 30339-3064

Mr. C.R. Oberg'

Public Utility Commission of Texas7800 Shoal Creek Blvd., Suite 400 NorthAustin, TX 78757

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INDETERMINATE EQUIPMENT QUALIFICA110N STATUS OF RESISTANCE TEMPERAIJREDETECTORS IN THE FUEL-BUILDING FILTER TRAINS

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On 12/23/91, with the reactor in operational condition 4, it wasdiscovered that'from 6/4/91 to 6/8/91,-fuel was moved in the fuel

|-building while resistance temperature detectors'(RTDs) installed in the

j fuel building heater trains were not environmentally and seismicallyqualified. Thus, the fuel building filter-trains are considered to.havebeen inoperable. Therefore, this report is submitted pursuant'to10CFR50.73 (a) (2) (i) (B) ' as operation prohibited by ' the TechnicalSpecifications.

The subject RTDs have been replaced with qualified models. Training! will be provided on the importance of communication when performing! operability analyses.|

| -GSU has performed an ambient humidity. analysis and a decay time analysisfor.the_ fuel-in the spent fuel pool. The results show that it was

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unlikely that fuel building charcoal filter efficiency was degraded andthat 1f a fuel handling accident had occurred, offsite doses would have

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I been bounded by the design basis fuel handling accident calculation.|

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REPORTED CONDITION

.On 12/23/91,. With the reactor in Operational Condition 4, it wasdiscovered that from 6/4/91 to 6/8/91, fuel was moved in the fuelbuilding (*ND*) while resistance temperature detectors (RTDs) (*26*)installed in the fuel building heater trains (*VG*) were notenvironmentally and seismically qualified. Thus, the fuel buildingfilter trains (*VG*) are considered to have been inoperable. Therefore,this report is submitted pursuant to 10CFR50.73 (a) (2) (1) (D) as operation-prohibited by the Technical Specifications. ,

INVESTIGATION

A review of Pyco RTD documentation was performed by GSU as a result of a.

10CFR21 notification issued by Niagara Mohawk Power Corporation. GSU's. investigation identified RTDs in the standby gas treatment system (SGTS)( * B:|* ) filter trains, control building chilled water system (*VI*), and-the fuel building filter trains (*VG*) as not being environmentally orseismically qualified.-The RTDs provided by Stone and WebsterEngineering Corporation (SWEC) for River Bend Station (RDS) werr,-notinstalled to Pyco's designed and qualified configuration. SWECredesigned the original qualified Pyco configuration for Model 222-4030RTDs_(*26*) to allow installation without a thermowell to improve theresponse time. This specific Pyco RTD model regttires a thermowell inorder to provido a moisture proot seal per Pyco test report 16436-82N,Rev. 5. This deficiency could cause-moisture intrusion into the RTD'selectronic components, resulting in failure. SWEC performed anengineering-analysis of this configuration (installed under E&DCR P-.41,000) and determined it to be qualified. However, the availableinformation supporting this position was inadequate. Therefore, the RTDs:could not be considered environmcntall,y qualified. The absence of thethermowell also rendered the RTDs seismically unqualified.

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In April 1991, an operability analysis was performed on the systemsy affected by the RTD problem. The fuel building filter trains (*VG_*) were' determined to be operable for normal operations, no fuel _ movement, with

'the RTDs seismically and environmentally unqualified. The operability ofthe fuel building filter trains (*VG*) during fuel movement was notconsidered at that time because no fuel movement was taking place and nofuel movement was expected to take place until the fourth refueling; outage (RF-4)..A modification request was initiated (MR 91-0039) to, replace these RTDs; however, the replacement was not implemented priorto.the fuel movement during a failed fuel inspection that took placefrom 6/4/91 to 6/8/91. Proper administrative controls were not pu' inplace prior to RTD replacement.

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A tracking limiting condition for operation (LCO) TR 91-136 wasinitiated on-8/24/91. This tracking LCO prohibits entry into OperationalCondition */RF-4 (fuel handling per the applicability statement of

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Technical Specification 3.6.5.6) prior to RTD replacement. The concernthat prompted its initiation is the possibility of a full core off-loadduring RF-4. A hypothetical accident could occur in which the higherheat load in the pool could cause boiling in the pool and thus put thefilters in a harsh (i.e., steam) environment. This was not a majorconcern during the tuel inspection because the heat load in the pool waslower and there was no possible accident which would cause a harshenvironment to exist.

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Tne operability analysis that was performed for both the SGTS and fuelbuilding filter trains was adequate. The urgency of the SGTS operabilityanalysis overshadowed the proper documentation and communication of theassumptions and conditions that went into the fuel building filter trainoperability analysis. The root cause was that the basis of the analysiswas not properly communicated which led to insufficient implementationof administrative controls. It should have been communicated thatoperability had not been determined for the condition of moving fuel inthe fuel building.

A similar event was identified in LER 91-007. In this case, the SGTS wasconsidered to have been inoperable due to the questionable qualificationstatus of the Pyco RTDs. An operability analysis defined acceptableauxiliary building humidity levels for which the SGTS could beconsidered operable with the unqualified RTDs. This analysis permittedRTD replacement while maintaining the SGTS operable. As previouslystated, the original Pyco RTD design was redesigned by SWEC andavailable documentation did not support qualification of the installedconfiguration.

QORRECTIVE ACTION

As previously stated, LCO TR 91-1M served as an administrativerestriction on entering Operational Condition * prior to RTD repair orreplacement. However, the original RTDs have been replaced withqualified models, and thus the LCO has been cancelled.

Training will be provided for the Engineering Analysis Group on theimportance of communication when performing operability analyses. Thisevent will be used as an example. This training is currently scheduledto be completed by 3/4/92.

SAFELY ABBESSMENT

One of the intended functions of the fuel building filter trains is tomitigate the consequences of a fuel handling accident (FHA) by limiting

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offsite doses to within 10CFR100 guidelines. The design basic FHAcalculation (PR(C)-418) is a boLnding calculation which determines thedose from an FHA assuming a filter efficiency of 99%, a bundle drop frommaximum height, a maximum broakage of pins, and a decay time of 24hours.

The concern with the RTDs is that if the RTDs fail to ope.ata properly,the_ heater may not operate. If the heater falls, the humidity of theair passing through the filter will increase. This can degrade theefficiency of the filter and therefore, its ability to removeradioactive iodines. Thus,.with degraded RTDs, the design basis FHAcalculation may not'be bounding.

The safety assessment of this event considered two approaches. The firstwas to assume that the ambient humidity was equal to the humidity of thefuel building and then determine if the filter efficiency was degradedat the time of fuel movement. The second approach was to calculate,based on_the spent: fuel poc1 loading at the time of the fuel movement,the time it would take for the radiciodines to decay to the point atwhich the calculated doses would be bounded by the FHA without takingcredit for the charcoal filter trains at all (0% efficiency).

LUIENT HUMIDITY ANALYSIS

The. filter efficiency would have degraded enly if the relative humidityin the Fuel Building was above 95%. The bumidity inside the building.is driven by the moisture content of the outside air, the moisture addedby the spent fuel-pool, and the moisture removed by the fuel buildingunit coolers.- It is difficult to quantify.the relative humidity in thefuel-building during the failed fuel inspection because of the lack ofinformation about the ambient conditions'both inside and outside thebuilding.-

The relative humidity outside during the failed fuel inspection did notrise above 95%-at Ryan. Airport (National. Weather Service Information).The relative humidity at River Bend is' expected to be similar to that atRyan Airport. Also, one radwaste chiller was operating throughout thefuel' inspection (per auxiliary control room logs), so cooling wasavailable to the fuel building unit coolers. Given what is known aboutthe-ambient conditions, it is unlikely that the relative humidity in thefuel building exceeded 95% during the inspection. Since this providesonly a qualitative analysis having the crude assumption that the fuelbuilding humidity was similar to that at Ryan Airport, a decay timeanalysis was perfcrmed.

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DECALTlHE ANALYSIR

In an FliA, the offsite and control room doses are due to the release offission product gases from the fuel building. Using a conservativecalculation, GSU has determined that a 57 day decay time will temove atleast as much of the initial activity of the fission gases as a 99%efficient charcoal filter. Note that the design basis Fila calculationassumes that an Fila cannot occur until 24 hours following-shutdown, thus-providing a 24 hour decay time following shutdown. Therefore, if thedecay time of the spent . fuel is 58 days, then the calculated doses willbe within the design basis Fila calculation, even if filter efficiency isdegraded to 0%.

,

Spent fuel-was moved for a failed fuel inspection which started at 1424hours'on 6/4/91 and ended at 1209 hours on 6/8/91 (por control roomlogs). All of the. fuel in the pool had decayed since the beginning ofthe third refueling outage, approximately 9 months beforo. This decay-time is significantly greater than 58 days; therefore, if an Fila had-occurred, the offsite doses would have been bounded by thoso calculatedin the design basis Fila calculation.

,

Another reason why the design basis Fila calculation was conservative isthat the. fuel movement was not directly over other spent fuel. Thiscareful planning ensured that if a bundle was dropped, it would not dropdirectly on other spent fuel. Since a direct drop was not-apossibility, the_ number of pins assumed to break in the design basis Filacalculation is greater than the number of pins that could actually havebroken.

CONCLESIONE

The ambient humidity analysis shows qualitatively that it was unlikely'that fuel building humidity levels exceeded 95%. Thus, even if it isassumed that the FTDs fail, followed by the heaters, it was unlikelythat the fuel building charcoal filter efficiency was degraded during.the fuel movement.

-The decay _ time analysis demonstrates that even_1f the worst case isassumed,_that the fuel building filter train charcoal filters wereoincapable of performing their design function, offsite doses would stillbe bounded by-the design basis' Fila calculation,

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