ML20009F580
| ML20009F580 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 07/02/1981 |
| From: | Mills L TENNESSEE VALLEY AUTHORITY |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| REF-PT21- 10CFR-050.55E, 10CFR-50.55E, NCR-SWP-79-S-5, NUDOCS 8107310327 | |
| Download: ML20009F580 (3) | |
Text
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OFFICIAL Copy I
400 Chestnut Street Tower II y
,- ou July 2, 1981
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j Mr. James P. O'Reilly, Director Office of Inspection and Enfercement gUL 3 01981= y
(~6; u ra,ca. gut,,j U.S. Nuclear Regulatory Cocaission Region II - Suite 3100 g
([t 101 t:arietta Street G
Atlanta, Georgia 30303 T
Dear Mr. O'Reilly:
SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 - EXCESSIVE OUTPUT FLUCTUATIONS OF FOX 3ORO INSTRUMENTATION - NCR SWP-79-S ADDITIONAL INFORMATION The subject deficiency was initially reported to NRC-0IE Inspector M. J. Gouge en August 28, 1979 in acco:.ance with 10 CFR 50.55(e).
Interim reports were submitted on September 26 and October 30, 1979, February 5, and August 11, 1980, and February 9 and March 24, 1981.
This noncenformance report was closed for unit 1 by inspection report 50-327/80-16 and for unit 2 by inspection report 50-328/81-23 Enclosed is additional information. We consider 10 CFR 21 applicable to this deficiency.
If you have any questions, please get in touch with D. L. Lambert at FTS 857-2581.
Very ' ruly yours, TENNESSEE VALLEY AUTHORITY L. M. Mills, Manager Nuclear Regulation and Safety Enclosure cc:
Mr. Victor Stello, Director (Enclosure)
Office of Inspection and Enforcement U.S. Nuclear Regulatory Comission Washington, DC 20555 Sdd OO$0$$y PDR W
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ENCLOSURE i
SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 e
I EXCESSIVE OUTPUT FLUCTUATIONS OF FOXBOR0 INSTRUMENTATION NCR SWP 79-S-5 10 CFR 50.55(e)
ADDITIONAL INFORMATION Description of Condition E= pit ~ees at Sequoyah Nuclear Plant have noted erroneous output signals I
coming from Foxboro equipment containing magnetic amplifiers (current /
i current repeaters and square root converters). This instrumentation was i
supplied by Westinghouse on the NSSS contract. The equipment is not perfor=ing according to the specifications in the Foxboro Equipment Manual.
which specifies that this equ'pmenc is to have an accuracy of + 1/2 percent with input voltage variations of + 10 percent. Tests have shown that 1.5 and 4.5 percent input variations resulted in 5.0 and 15.5 percent output 4
j current changes. These excessive output variations have caused spurious j
operaticns of plant equipment by producing erroneous safsty injection signals. Some of the Foxboro units are used to actuate safeguards 4
equipment and to initiate teactor trip signals. There are 168 modules per I
unit containing magnetic a=plifiers at Sequoyah Nuclear Plant, j
Safety I=plications These Fcxboro cocponents are a part of essential safety-related circuits.
Erroneous safety injection signals and spurious operation of safety-related equf o=ent are degrading to these safety syste=s and could adversely affect the cafe operation of the plant during certain operational codes.
Additional Information TVA has thoroughly investigated this problem and has cet with Westinghouse j
and Foxboro to determine the causes of the problem and to discuss possible solutiens. The follcwing conclusions were made by Westinghouse:
1.
The magnetic amplifier with its line voltage compensttion circuitry is i
an inherently slow device.
The compensation c'.rcuit can correct'for l
line voltage deviations of + 10 percent only if the voltage fluctuation j
is very slow. The modu ~ es cannot correct for the type of voltage transients and fluctuatiens that normally occur in the line voltage.
2.
The magnetic a=plifiers will perform acceptably if they are supplied
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with a closely regulatec power source.
i With these conclusions in mind, TVA has replaced the inverters at Sequoyah in ceder to better regulate the power supply. Tests have shown that the
=agnetic amplifier fluctr;cion? can be limited to approximately one percent with the improved power supply.
Ittis change of inverters enables the magnetic amplifiers to perform acceptably under present inverter loading conditions.
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%t TVA's request, Westinghouse has developed and tested a field
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modification kit for the Foxboro I/I repeaters. Test results indicate a significant improve =ent in performance of the I/I repeaters. The modification involves r>gulating the output of the module's de power supply which is the primary suurce of magnetic amplifier instability.
Westinghouse is also develaping a modification for the square root converters which is scheduled to be tested in the near future. TVA will implement this field modification of the Foxboro instruments.
Field tests will verify the Westinghouse test results.
These modifications constitute the final corrective acticn for this deficiency.