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400 Chestnut Street Tover II

Fare" 13, 1c?1

N< GTIVto A?.!r'ffgN/SSfg11r. Janes ?. O'Reitir, Director

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Office of Inspection an'. Enforcer.ent>U.S. 'Nelear Pegulatory Cemnission ,, g 7

Region II - Suite 3100 b101 Marietta Street dAtle.nta, Georgia 30303 AsI wDear t'r. O'Reilly:

07F C" 0F I!'SPECT10'4 AND E ! FORCE?'S'IT FULLE'"I'? 90-25 - RII:JPG. 0 -?5 e -?f' >oA - 9 ROT!S FEFRY !!UaLEAR PLA!P

In respon::e to your December 10, 1090, letter to H. G. Pearts 'ehichtransmitted OIE Bulletin 80-2;, enclosed ?"e the results of ouainvestigations for our Browns Ferry Nuclear Plant.

k'e estimate that 137 nan-hours were expended in the prec3 ration ofthis response. If you have any questions regarding this natter,please call Jim Doner at FTS 857-201a.

To the best of my knowledge, I declare the statements containedherein are complete and true.

Very truly vours,

TFN!'ESSEE VALLEY AUTHOPITY

L. ". ' tills, ?"anager'

!'uclear Regulation and Safety

Enclosurecc: Mr. Victor Stello, Director (Enclosure)

Office of Inspection and EnforcementU.S. Muclear Regulatory CommissionWashire; ton, DC 20555

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ENCLOSURE

RESPONSE TO OIE BULLETIN 80-29BRO'dNS FERRY NUCLEAR PLAMT

ITEM 1

If your facility has not yet installed or changed or is presentlyin the process of changing to the two-stage S/R valves, initiateappropriate quality control procedures to ensure inspection of the

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solenoid actuators for excess Loc-tite prior to operation. If thesolenoid actuator manufactured by Target Rock Corporation is alreadyinstalled in your facility, confirm its operability either by itsoperational performance (i.e., it has functioned as designed following anaging period of about 3 months in the higher temperature environment ofpower operating conditions) or by functional testing at full pressureduring the next refueling shutdown of the facility. Include in yourreport the results of all attempts to operate the two-stage S/R valve (s).

RESPONSE

We have purchased a total of 39 two-stage Target Rock valves from the,

General Electric Company (GE) for our Browns Ferry Nuclear Plant units 1,2, and 3 Most of these valves have already been in service for at leastone fuel cycle. Subsequent steam bench testing or postmaintenancetesting of the solenoid valves has not indicated any problems fromexcessive application of Lec-tite. However, we have identified sevenvalves on Browns Ferry unit 1, three valves on unit 2, and one valve onunit 3 that are now installed on which the solenoids have not seen priorservice. Since these solenoids have not been actuated after an agingperiod of at least three months at operating temperatures and pressures,the appropriate procedures will be initiated to functionally test thesevalves during the-next refueliag shutdown. We are also preparing theappropriate quality control procedures to ensure an inspection forexcessive Loc-tite of all new solenoids that may be' purchased in thenear future and following any maintenance that may be performed on thesolenoid valves. We have also been informed by the Target RockCorporation that it has initiated the proper controls to alleviate theproblem on future solenoid assemblies.

A followup report will be submitted describing the results of thefunctional testing of the seven two-stage valves on unit 1, the threevalves on unit 2, and the one valve on unit 3

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ITEM 2

In the event that a S/R valve, regardless of make or model (e.g. , bothtwo or three stage), fails to function as designed, excepting forpressure setpoint requirements, and the cause of the malfunction is notclearly determined, understood, and therefore corrected, standardoperating procedures shall require that the entire valve be removed fromservice, disassembled, inspected, adjusted, and pressure setooint testedwith steam for proper operation prior to returning the valve to service.These overhaul requirements shall be at least equivalent to those

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applicable to periodic surveillance rehabilitation requirements.Appropriate revisions to your operating procedures shall be made toinclude these requirements.

RESPONSE

The Browns Ferry technical specifications already have the appropriateoperating limitations in place to fulfill your requirements. Ourprocedures now require that each valve be steam tested following anymaintenance that will affect the setpoint or operability. Furthermore,to alleviate the possibility of an event occurring as you describe, weperform (1) a functional test of the solenoid valve to confirm itsoperability before startup of the unit and (2) a functional test of theentire valve at approximately 250 psig reactor pressure during startup.Therefore, we believe that the necessary procedures to prevent anoccurrence of this type are already being administered at Browns Ferryand no further revisions are necessary.

ITEM 3

A review of your S/R valve pneumatic supply systems shall be performed to.

determine the potential for and magnitude of an overpressure condition.The determined overpressure potential of the pneumatic supply shall be

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compared with the maximum operating pressure capabilities of the solenoidactuator valves serving the S/R valves, so es to determine whether suppivpressure could result in valve malfunction. Protective devices (such asrelief valves) shall be installed in the proxinity of the S/R valves andset to protect against supply pressure in excess of the operatingpressure capabilities of the solenoid actuator device. In addition,-consideration should be given to modification or replacement to reducethe sensitivity of the solenoid actuator to pneumatic supplyoverpressure. Further, the failure, either high or low, of the pneumatic

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supply syst'em pressure should be measured at a location as close as. practicable to the S/R valves and downstream of any check valveconnecting two or more pneumatic sources. Appropriate operatingprocedures shall be provided ,to guide operator response to such anoccurrence of high or low supply pressure.

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RESP 0'rSE

The drywell control air svstam of each reactor unit consists of twocompressors which discharge into a common header before the headerpenetrates the drywell. The compressors are in parallel so that oneserves as a redundant backup to the other. These comoressors arecaoable of operating continuously and are designed to shut off at 100psig and start at 85 psig. A low-pressure alarm which annunciates in themain control room is installed on the common header and set to alarm at80 psi , Both air compressors are equipped with a safety valve set at -115 psig on the discharge line. The backup to the drvuell control airsystem is the plant control air systen. However, during normal operationthis supply is manually isolated from the drvwell control air system,but it could supply air to the drywell system when drywell air pressuredrops below 90 psig and the isolation valve is open. The plant controlair system is also protected by safety-relief valves located at eachcompressor and set at 115 psig.

Each main steam safety-relief valve control air supply is on a separatebranch connected to the control air header inside the drywell. Six ofthe safety-relief valves are provided for the autonatic depressurizationsystem (ADS). Their suppiv branch consists of a normally open isolation

. valve, a check valve, a pressure switch, and an. accumulator. The checkvalve ensures a normal air pressure will be maintained in the accumulatorfor multiple actuations of the ADS valves upon a loss of control air.The pressure switch on each branch is set to actuate a low-pressure lightand alarm in the control room when control air pressure drops below 70psig. The remaining safety-relief valve control air supplies are onseparate branches with each having a normally open manual isolationvalve.

The safety-relief valve control air supply system is inspected and tested4during each refueling in accordance with plant procedures. This testingand inspection are performed to ensure that the system remains leak tightand will functionally operate as designed. The pressure switches locatedon each supp1v branch of the ADS valves are insoected and calibratedduring the system test.

Therefore, after reviewing Browns Ferry safety-relief valves' pneumaticsupply system, we believe that the potential for overpressurization tothe magnitude of inadvertently opening a safety-relief valve does notexist. In addition, we believe that the drywell control air system isadequately designed with overpressure protection devices and systempressure detection instrumentation and no further modifications are

necessary at this time. Operating instructions address operator responseto low supply pressure.

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Although we have not experienced the problems with the Taanet-Rocktwo-stage safety-relief valve as you have desnribed, we have ancounteredanother problen with the solenoid valves. We have determined that thesolenoid valve is very susceptible to damage during maintenance andhandling of the Target Rock two-stage valve. This damage can be causedby applying a relatively small force to the coil housine on the solencid.This load on the coil nay, in turn slightiv distort the thin wall of the, ,

bonnet tube.

We have found that, after this damage has occurred, the solanoid willappear to function normally by opening when energined but that the *

solenoid valve will usually not travel fully to the closed position whendeenergized. This condition will keep the pneumatic actuator in the openposition and allow the main valve to open when sufficient system pressurais applied (approximately 50 psi). To date, we have experiencedapproximately four failures of this type. These failures have beendetected and corrected before returning the unit to operation because TVAis exercising the necessary precautions during handling, installation,and preservice verification of the safety-relief valve. However, ifthese precautions are not taken, we helieve this damage could occur andrenain undetected before unit restart. Although it is our undarstandirqthat this type of failure has occurred oniv at 3rowns Farry, ve believethis information may be of some benefit to other utilities which are nowusing the Target-Rock two-stage safetv-reiter valve.

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