ML20235Z469
| ML20235Z469 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 07/20/1987 |
| From: | Gridley R TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| IEB-86-002, IEB-86-2, NUDOCS 8707270307 | |
| Download: ML20235Z469 (6) | |
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ENNESSEE VALLEY AUTHORITY '
CH ATTANOOG A, TENNESSEE 37401 SN 157 Lookout Place JUL 201987 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C.
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Gentlemen:
In the Matter of
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Docket Nos 50-259 Tennessee Valley Authority
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50-260 50-296 f
BROWNS FERRY NUCLEAR PLANT - NRC OFFICE OF' INSPECTION AND ENFORCEMENT (IE)
BULLETIN 86 STATIC "O" RING (SOR) DIFFERENTIAL PRESSURE SWITCHES This letter provides.the Browns Ferry response to IE Bulletin 86-02 dated-July 18, 1986. Please note that this response is within the' alternate schedule l
provided in the bulletin for plants;in an extended shutdown.. Enclosure 1 contains information required by the referenced bulletin.
identifies commitments made in encloe re 1.
Should additional information on this, subject be required, please refer any questions to James T. Bennett, BFN Site Licensing, at (205) 729-2677.
Very truly yours, t
TENNESSEE VALLEY AUTHORITY l
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R. C idley,.Di ctor Nuclear Safet and Licensing.
Enclosures cc:
Seu page 2 f59 PDR
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An Equal Opportunity Employer tL n
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4 l i U.S. Nuclear Ret;ulatory Commission
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I ce (Enclosures):
Mr. G. G. Zech, Assistant Director Regional Inspections Division of'1'VA Projects office of,ippecial Projects U.S. Nuclear Regulatory Commission Region II j
101 Marietta St., NW, Suite 2900 j
l Atlanta, Georgia 30323
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Mr. J. A. Zwolinski, Assistant Director for Projects j
Division of TVA Projects
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l Office of,Special Projects U.S. Nuclear Regulatory Commiscion 4350 East West Highway EWW 322
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Bethesda, Maryland 20814 j
j Browns Ferry Resident Inspector Browns Ferry Nuclear Plant Route 2, P.O. Box 311 Athens, Alabama 35611 l
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ENCLOSURE 1 RESPONSE TO IE BULLETIN 86-02 BROWNS FERRY NUCLEAR PLANT (BFN)
Item 1 Within seven (7) days, submit a report on the extent te which SOR Model 102 or 103 differential pressure switches are installed (or planned) as electrical equipment important to safety, as defined in 10 CFR 50.49(b).
Include in the report:
the model number of the switch, the system in which it is installed (e.g., low pressure safety injection), the application of the switch (e.g.,
water level measurement, system flow measurement), and the function of the switch (e.g., control of minimum flow recirculation valve). A negative report, if appropriate, is required.
BFN's Resronse Two SOR differential pressure (DP) switches (model No. 103 AS-B212-NKJJTTX6) are being installed on unit 2 in the Residual Heat Removal (RHR) system as part of the environmental qualification upgrade program.
These switches (BFN device Nos. 2-FS-74-50 and 2-FS-74-64) are used to open valves in the RHR minimum flow recirculation lines so that adequate cooling to pump seals and bearings is provided when system flow is low. The same model SOR Dp switches are currently planned to be installed on unit 1 and unit 3 RHR minimum flow system before restart of the respective units.
Item 2 Within seven (7) days, take positive action to assure that licensed reactor operators on duty are prepared for potential malfunctions of SOR switches.
BFN's Response Sufficient setpoint margin is provided to ensure reliable switch operation; therefore, the need for special operator training is not necessary.
Item 3 Within 30 days, conduct a special test of each SOR switch to determine if the switch and system function properly cr if short-term corrective actions are necessary. The tests are to determine if the switches / systems will respond acceptably on the first demand af ter being at system operating conditions for a period of time.
The tests should be planned and conducted so as to minimize l
any potential adverse effects of the testing.
If any corrective action includes the replacement of SOR switches with mechanical Dp switches by another manufacturer, the licensee should submit a technical justification, including a reliability demonstration. Repeat the special tests on a monthly basis until two consecutive successful tests are attained.
BFN's Response This item is not applicable since BFN is not in operation and the switches are not currently installed. Long-term corrective action for Item 6 obviates the need for this short-term action.
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t I Item 4 Report f ailure in accordance with 10 CFR 50. 72 and 10 CFR 50.73.
BFN',s_ Response No failures ha,ve occurred to date; however, BFN is required to report any failures that could prevent fulfillment of a safety function in accordance f
with 30 CFR 50.72 and 10 CFR 50.73.
Iten S Within 60 days, develop, impicment, and submit a written report describing your interim performance monitoring program to provide continuing assurance that the performance of the switches and plant systems remains acceptably reliable until long-term corrective actions are fully implemented.
J BF('s Response This item is not applicable since BFN is not in operation and the switches are not currently installed. Long-term corrective action in Item 6 will obviate the need for un interim program.
Item 6 Within 60 days, nubmit a written report
-h describes the margin and basis for switch actuation. The report shoulJ
.so describe the long-term corrective actions to be taken, including the implementation schedule, the impacts of potential common acde failures, and an analysis to demonstrate that the system involved will meet regulatory requirements and function reliably.
The report should include specific information on the installed SOR switches, the manufacturer's specified range for the switch, the nominal and allowable values for the calibration setpoint in the technical specifications in the same terms as the manufacturer's specified range for the switch, the relative locations of the instrument taps for water level monitoring applications, sources of systematic errors such as the differences in elevations of the installation of condensing pots, and "as four.d" and any subsequent test data fo? any switch that does not conform to the technical specifications or is otherwise unacceptable.
I BFN's Response In determining the margin and basis for switch actuation, two possible failure modes were evaluated.
The failure modes are the minimum flow always open and minimum flow not open during low flow conditions.
For the case where the minimum flow valves fail to isolate, a low-pressure coolant injection (LPCI) flow analysis was performed to determine the amount of flow delivered to the reactor pressure vessel (RPV). The results obtained indicate a failure of both minimum flow lines would not divert sufficient flow from the RPV to invalidate design basis operation.
Therefore, flow diversion due to the
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l failure of the RHR uinimum flow valves is insignificant.
The other failure j
node where the minimum flow line does not.open during low flow conditions is the most critical since it creates a potectial for pump heatup. The minimum flow switch setpoint is not referenced in the technical specifications; however, a design flow of 1,000 gpm is used to protect the pumps. The manufacturer's nominal range for the switch is 10 to 100 inches water column (w.c.) and the rated minimum decreasing setpoint for the switches is 3 inches w.c. (= 3000 gpm). Margin calculations for the switches setpoints are based upon an evaluation of SOR test data for the specific models supplied to BFN.
Instrument errors that could cause the setpoint to move below the minimum tecreasing range limit and prevent the valve from opening were considered.
To prevent changes in the setpoint (due to temperature, radiation, seismic, etc.)
from preventing switch actuation, the rated minimum setpoint of 3 inches was multiplied by a factor of two. Additional margin of 3.36 inches w.c. was used to compensate for static pressure shift, repeatability, and drift and then added to twice the rated minimum setpoint (2 x 3.0 inches w.c. + 3.36 inches w.c. = 9.96 inches w.c.
(= 5,500 gpm)). T -p protection is ensured because the adjusted setpoint derived from the above calculations (5,500 gpm) provides er sufficient setpoint margin (2,500 gpm) above the rated minimum decreasing setpoint (3,000 gpm) to ensure reliable switch operation.
In addition, TVA is currently evaluating SOR's long-term test data obtained to date, which determines setpoint stability as documented in SOR test report 8601-042, dated March 1987. Upon completion of the evaluation, TVA will adjust the setpoint for more margin, if necessary, to compensate for instrument error not already bounded by the above calculations.
The long-term corrective actions will be to implement maintenance instructions which have been prepared to perform and check calibration of the setpoints for the RHR switches. After initial calibration, the instructions will be performed semiannually to verify setpoint calibration until two consecutive successful tests are attained. These instructions will include steps to record the first actuation as the "as-found" reading for the setpoints.
Swicch performance to automatically open and close the minimum flow valves will also be monitored during RHR pump flow rate testing which is performed on 4
a quarterly surveillance frequency.
Sufficient flow and valve position indication are available in the control room for the operator to assess minimum flow operability during testing.
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Since the switches have not yet been calibrated, no "as found" data is available; however, if future calibration checks indicate unacceptable readings a report will be performed in accordance with 10 CFR 50.72 and 10 CFR 50.73.
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ENCLOSURE 2 BROWNS FERRY NUCLEAR PLMT LIST OF COMMITMENTS MADE IN ENCLOSURE 1 1.
Evaluate SOR Test Report 8601-042 dated March 1987,.and if necessary, adjust setpoint for more martin to compensate for instrument drift not already bounded by margin calculations.
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Perform maintenance instructions semiannually until two consecutive tests are attained.
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Revise RHR pump flow rate test to include steps to verify RHR minimum flow system switch operability.
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