ML19347D729
| ML19347D729 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 03/18/1981 |
| From: | Mills L TENNESSEE VALLEY AUTHORITY |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| IEB-80-25, NUDOCS 8103261180 | |
| Download: ML19347D729 (5) | |
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400 Chestnut Street Tover II Fare" 13, 1c?1 N< GTIVto A?.
!r'ffgN/SSfg 11r. 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 b
101 Marietta Street d
Atle.nta, Georgia 30303 AsI w Dear t'r.
O'Reilly:
07F C" 0F I!'SPECT10'4 AND E ! FORCE?'S'IT FULLE'"I'? 90 RII:JPG
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>oA - 9 ROT!S FEFRY !!UaLEAR PLA!P In respon::e to your December 10, 1090, letter to H. G. Pearts 'ehich transmitted OIE Bulletin 80-2;, enclosed ?"e the results of oua investigations for our Browns Ferry Nuclear Plant.
k'e estimate that 137 nan-hours were expended in the prec3 ration of this 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 contained herein are complete and true.
Very truly vours, TFN!'ESSEE VALLEY AUTHOPITY L. ". ' tills, ?"anager
!'uclear Regulation and Safety Enclosure cc:
Mr. Victor Stello, Director (Enclosure)
Office of Inspection and Enforcement U.S. Muclear Regulatory Commission Washire; ton, DC 20555 siosseo //(#:
ENCLOSURE RESPONSE TO OIE BULLETIN 80-29 BRO'dNS FERRY NUCLEAR PLAMT ITEM 1 If your facility has not yet installed or changed or is presently in the process of changing to the two-stage S/R valves, initiate appropriate quality control procedures to ensure inspection of the solenoid actuators for excess Loc-tite prior to operation.
If the solenoid actuator manufactured by Target Rock Corporation is already installed in your facility, confirm its operability either by its operational performance (i.e., it has functioned as designed following an aging period of about 3 months in the higher temperature environment of power operating conditions) or by functional testing at full pressure during the next refueling shutdown of the facility.
Include in your report 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 least one fuel cycle. Subsequent steam bench testing or postmaintenance testing of the solenoid valves has not indicated any problems from excessive application of Lec-tite. However, we have identified seven valves on Browns Ferry unit 1, three valves on unit 2, and one valve on unit 3 that are now installed on which the solenoids have not seen prior service. Since these solenoids have not been actuated after an aging period of at least three months at operating temperatures and pressures, the appropriate procedures will be initiated to functionally test these valves during the-next refueliag shutdown. We are also preparing the appropriate quality control procedures to ensure an inspection for excessive Loc-tite of all new solenoids that may be' purchased in the near future and following any maintenance that may be performed on the solenoid valves. We have also been informed by the Target Rock Corporation that it has initiated the proper controls to alleviate the problem on future solenoid assemblies.
A followup report will be submitted describing the results of the functional testing of the seven two-stage valves on unit 1, the three valves on unit 2, and the one valve on unit 3
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_2 ITEM 2 In the event that a S/R valve, regardless of make or model (e.g., both two or three stage), fails to function as designed, excepting for pressure setpoint requirements, and the cause of the malfunction is not clearly determined, understood, and therefore corrected, standard operating procedures shall require that the entire valve be removed from service, disassembled, inspected, adjusted, and pressure setooint tested with steam for proper operation prior to returning the valve to service.
These overhaul requirements shall be at least equivalent to those applicable to periodic surveillance rehabilitation requirements.
Appropriate revisions to your operating procedures shall be made to include these requirements.
RESPONSE
The Browns Ferry technical specifications already have the appropriate operating limitations in place to fulfill your requirements.
Our procedures now require that each valve be steam tested following any maintenance that will affect the setpoint or operability.
Furthermore, to alleviate the possibility of an event occurring as you describe, we perform (1) a functional test of the solenoid valve to confirm its operability before startup of the unit and (2) a functional test of the entire valve at approximately 250 psig reactor pressure during startup.
Therefore, we believe that the necessary procedures to prevent an occurrence of this type are already being administered at Browns Ferry and 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 compared with the maximum operating pressure capabilities of the solenoid actuator valves serving the S/R valves, so es to determine whether suppiv pressure could result in valve malfunction. Protective devices (such as relief valves) shall be installed in the proxinity of the S/R valves and set to protect against supply pressure in excess of the operating pressure capabilities of the solenoid actuator device.
In addition,
-consideration should be given to modification or replacement to reduce the sensitivity of the solenoid actuator to pneumatic supply overpressure. Further, the failure, either high or low, of the pneumatic supply syst'em pressure should be measured at a location as close as
. practicable to the S/R valves and downstream of any check valve connecting two or more pneumatic sources. Appropriate operating procedures shall be provided,to guide operator response to such an occurrence of high or low supply pressure.
. RESP 0'rSE The drywell control air svstam of each reactor unit consists of two compressors which discharge into a common header before the header penetrates the drywell. The compressors are in parallel so that one serves as a redundant backup to the other.
These comoressors are caoable of operating continuously and are designed to shut off at 100 psig and start at 85 psig.
A low-pressure alarm which annunciates in the main control room is installed on the common header and set to alarm at 80 psi, Both air compressors are equipped with a safety valve set at 115 psig on the discharge line. The backup to the drvuell control air system is the plant control air systen.
However, during normal operation this supply is manually isolated from the drvwell control air system, but it could supply air to the drywell system when drywell air pressure drops below 90 psig and the isolation valve is open.
The plant control air system is also protected by safety-relief valves located at each compressor and set at 115 psig.
Each main steam safety-relief valve control air supply is on a separate branch connected to the control air header inside the drywell. Six of the safety-relief valves are provided for the autonatic depressurization system (ADS). Their suppiv branch consists of a normally open isolation
. valve, a check valve, a pressure switch, and an. accumulator.
The check valve ensures a normal air pressure will be maintained in the accumulator for 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 light and alarm in the control room when control air pressure drops below 70 psig. The remaining safety-relief valve control air supplies are on separate branches with each having a normally open manual isolation valve.
The safety-relief valve control air supply system is inspected and tested 4
during each refueling in accordance with plant procedures.
This testing and inspection are performed to ensure that the system remains leak tight and will functionally operate as designed. The pressure switches located on each supp1v branch of the ADS valves are insoected and calibrated during the system test.
Therefore, after reviewing Browns Ferry safety-relief valves' pneumatic supply system, we believe that the potential for overpressurization to the magnitude of inadvertently opening a safety-relief valve does not exist.
In addition, we believe that the drywell control air system is adequately designed with overpressure protection devices and system pressure detection instrumentation and no further modifications are necessary at this time. Operating instructions address operator response to low supply pressure.
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i 4.
Although we have not experienced the problems with the Taanet-Rock two-stage safety-relief valve as you have desnribed, we have ancountered another problen with the solenoid valves. We have determined that the solenoid valve is very susceptible to damage during maintenance and handling of the Target Rock two-stage valve. This damage can be caused by 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 will appear to function normally by opening when energined but that the solenoid valve will usually not travel fully to the closed position when deenergized. This condition will keep the pneumatic actuator in the open position and allow the main valve to open when sufficient system pressura is applied (approximately 50 psi). To date, we have experienced approximately four failures of this type. These failures have been detected and corrected before returning the unit to operation because TVA is exercising the necessary precautions during handling, installation, and preservice verification of the safety-relief valve. However, if these precautions are not taken, we helieve this damage could occur and renain undetected before unit restart.
Although it is our undarstandirq that this type of failure has occurred oniv at 3rowns Farry, ve believe this information may be of some benefit to other utilities which are now using the Target-Rock two-stage safetv-reiter valve.
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