ML20150C920
| ML20150C920 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 03/11/1988 |
| From: | NRC OFFICE OF SPECIAL PROJECTS |
| To: | |
| Shared Package | |
| ML20127A683 | List:
|
| References | |
| NUDOCS 8803220422 | |
| Download: ML20150C920 (3) | |
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'o UNITED STATES 8-([ h NUCLEAR REGULATORY COMMISSION
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'E WA SHING TON, D. C. 20555 Ue SAFETY EVALUATION REPORT BY OFFICE UF SPECIAL PROJECTS EMPLOYEE C0hCERN ELEMENT REPORT 23511 "CONTROL SWITCH MALFUNCTION GIVES OPERATOR MISLEADING INDICATION OF VALVE POSITION" i
LENNESSEEVALLEYAUTHORITY SECUOYAH NUCLEAR POWER PLANT UNITS 1 AND 2 DOCKET NOS. 50-327/328.
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I.
SUBJECT Category:
Engineering (20,000)
Subcategory:
Electrical Safety (23,500)
Eler.ent :
Control Switch Malfunction Gives Operator Misleading Indication of Valve Position i
(23511)
Employeo Concern:
ECTG-3
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Element Report 23511, Revision 2 prepared March 31, 1987, involves an employee.
concern stating "Valve wiring circuits allow red and green lights to operate at reduced voltage and light dimly, if at all, upon a malfunction of the P-auto contact of the Westinghouse W-2 control switch on the unit control-board."
II.
SUMMARY
OF ISSUE The concern is that a W-2 switch malfunction could cause a misleading indica-tion of valve position.
The problem was first identified for TVA plants in the Black and Veatch Findings Report for Watts Bar (finding 112 10/27/82).
Additionally, NRC IE Bulletin 80-20. alerted TVA to the potential for W-2 switch malfunction.
TVA's response to NRC regarding compliance to IE Bulletin 80-20 stated that TVA would test and rrodify all safety related equipment utilizing W-2 switches.
TVA's response to the NRC on Bulletin IE 80-20 included an option, based on a Westinghouse recommendation, to replace W-2 switches with new W-2 switches manufactured under a new process.
After discussions with the NRC, Westinghouse reversed its position and eliminated the W-2 switch replacement option.
The 8803220422 080311 PDR ADOCK 05000320 P
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. reversal made necessary a revised final response by TVA as discussed in a TVA neco f~ rom Raulston to Mills, April 5, 1982.
However, no record could be found that a revised response had been submitted to iD.C.
Although the option-for replacement of the original W-2 switches with new W-2 switches had been rejected, TVA did replace certain W-2 switches with new
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switches manufactured by Electroswitch.
Neither drawings nor other documenta-tion could be found for the switch replacement nor could evidence be found that a revised final response had infomed the NRC of the switch replacement.
As a result of the wiring change, the sneak circuit was introduced inadvertently.
A sneak circuit can be defined as a path for electrical current, not intended by the circuit desioner, and which causes unexpected and, usually, unacceptable circuit functioning.
In this case, the sneak circuit could only exist if the W-2 switch contact, nomally closed in neutral position, would fail open, causing the valve position indicating lights to dim. The sneak circuit was later identified by Black and Yeatch on October 27, 1982, and was corrected by revision of ECN L5591.
Design drawing revisions to eliminate the sneak circuit were completeo June 8, 1984.
A TVA evaluation term found several discrepancies in the counting of W-2 switches and no evidence could be found of a program to prevent the recurrence of this problem in the future through possible circuit modifications.
TVA has certaitted to a number of steps which will be ccmpleted prior to restart:
1.
TVA will add a cautionary note to the switch contact development drawing to prevent future applications or replacement of W-2 switches or in the introduction of sneak circuit paths.
2.
TVA will identify all W-2 switches in safety related circuits.
3.
TVA vill review each type W-2 switch application to ensure that all failures which could result from spring return to neutral or sneak circuit will be detectable by the operators.
4 TVA will notify all plant operators of the possible failure mode of the W-2 switches and the effect on control board status indication.
TVA has ccamitted to a number of steps, including the following corrective actions which will be completed post restart:
1.
Revise the response to NRC IE Bulletin 80-20 to address the Reversal of the Westinghouse Positiun and the replacement of W-2 switches with Electroswitch Switches.
2.
Establish as-designed and as-constructed status listing of switch circuits.
- 3.
Revise the ECN L5591 to ensure inclusion of all applicable safety l
related switches and complete the actions required by ECN L5591.
1 4.
Verify that there are no switches with a sneak' circuit path.
III. EVALUATION NRC and its consultant, SAIC, reviewed the employee concern and prepared a request for additicnal information (RAI).
The RAI requested clarification of several TVA review efforts and requested a forecast completion date for the implementation of corrective action.
TVA provided additional information to NRC in an August 13, 1987, TVA to NRC letter.
TVA committed to review all W-?
switch applications and to advise operators of any switches which require modifications.
TVA committed to completing all reviews and modifications by April 1988.
Additionally, TVA will perform continuity checks every 31 days for i
switches requiring trodifications and will advise operators about the potential uisleading information from these switch indicators.
IV. CONCLUSION Based en our review, we find TVA's investigation, evaluation and the corrective acticn plans to resolve the employee concern as described in EN-23511 SQN, Rev. ? acceptable and believe that implementation of these corrective actions will close the issue.
Verificatien of corrective actions which TVA has identi-
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fied as a restart item should be verified by NRC inspectors in a future inspection.
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