ML20086N064

Final Deficiency Rept 84-01 Re Failure of Gould-Rundel four- Position Selector Switches.Initially Reported on 830824 & 840111.All Defective Switches Will Be Replaced

ML20086N064
Person / Time
Site:	Wolf Creek, Callaway, 05000000
Issue date:	02/09/1984
From:	Seiken S BECHTEL GROUP, INC., STANDARDIZED NUCLEAR UNIT POWER PLANT SYSTEM
To:	Jay Collins, James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III), NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
84-01, 84-1, SLNRC-84-0028, SLNRC-84-28, NUDOCS 8402170209
Download: ML20086N064 (10)

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SNUPPS Standardized Nuclear Unit Power Plant System s choke ch.,ry Road February 9, 1984 Rockwine, Maryland 20050 SLNEC 84-0028 FILE: 0491.10.2 SUBJ: Final Report: Gould/Rundel Selector Switch Failures, 10CFR50.55(e)

Report 84-01 Mr. James C. Keppler Administrator, Region III <

U.S. Nuclear Regulatory Commission 799 Roosevelt Road M@20W2  %

Glen Ellyn, Illinois 66137 3W dMr 900h'rP TNollins, y Administrator, Region IV -

U.S. Nuclear Regulatory Commission Suite 1000, Parkway Central Plaza Arlington, Texas 76012 Docket Nos. STN 50-482 and STN 50-483

Reference:

KGE Letter, G.L. Koester to W.C. Seidle dated 9/23/83:

Potential 10CFR50.55(e) Report-Gould/Rundel Handswitches Gentl emen:

Enclosed is a report concerning the failure of Gould-Rundel 4-position selector switches at the Callaway and Wolf Creek plants. The report is being submitted on behalf of Ur. ion Electric Company and Kansas Gas and Electric Company as a final Significant Deficiency Report as re-quired by 10CFR50.55(e).

The failure of the subject switches was initially reported to NRC Region IV (Johnson) for Wolf Creek on August 24, 1983, with the refer-enced interim report submitted on September 23, 19d3. A report on similar problems at Callaway was telephoned to NRC Region III (Pelke) by Union Electric Company (Laux) on January 11, 1984.

On the basis of further investigation, the 4-position selector switch failures were judged to be generic in nature resulting from a design deficiency in the switches. As ' indicated in the enclosed report, all; Callaway and Wolf Creek 4-position selector switches will be replaced

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by switches of modified design. The manufacturer, Gould/Rundel, will-be requested to notify other nuclear utilities of the problem with these switches and to consider reportability of these items under Part 21 regulations.

8402170209 840209 PDR ADOCK 050004P2 h

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SLNRC 84-0028 Page Two Please do not hesitate to call should there be any questions concerning this report.

Very trulp yours, a

S. J.VSeiken QA Manager RPW/dck/12b28 Enclosure cc: D. F. Schnell UE G. L. Koester KGE D. T. McPhee 4 CPL W. S. Schum NRC/WC J. H. Neisler fiRC/ CAL B. H. Little NRC/ CAL R. C. DeYoung NRC/IE: HQ J. E. Konklin NRC/IE: III

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FINAL REPORT-ON i

j SELECTOR SWITCH FAILURE PER

10CFR 50.55(e) i i

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SNUPPS PROJECT ~

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.PECHTEL POWER CORPORATION i

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TABLE OF CONTENTS PACE 1

1.0 Introduction 2.0 Description of Selector Switch 2 and Deficiency 3

3.0 Safety Implications 5

4.0 Resolution and Corrective Action 6

5.0 Conclusions 2

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1.0 INTRODUCTION

In August and September of 1983, during startup testing of the containment ventilation systems, deficiencies were discovered with I local selector switches provided by Gould in the SNUPPS Motor Control Centers at the Callaway (Union Electric) and Wolf Creek (Kansas Gas & Electric) stations.

In August of 1983, problems were encountered during startup testing of the Containment Air Coolers at the Wolf Creek station with the 4-position Gould-Rundel selector switches that were used as local handswitches. It was noticed that the switch cam became bound and improper contact operation resulted when the switch was operated.

In September 1983, similar problems were encountered during startup testing of the Hydrogen Mixing Fans at the Callaway station with identical switches. There, the selector switches exhibited erratic behavior such as binding, inconsistent continuity and indeterminant switch positioning.

The problems were documented on Startup Field Reports (SFR) at both sites (1-GN-4 at Wolf Creek and 2-GN-014A at Callaway). Upon learning of the deficiencies, the Kansas Gas and Electric Company reported this matter to the NRC as a potential significant deficiency under 10 CFR 50.55(e) criteria. A similar report was provided to the NRC by the Union Electric Company. The plant designer, Bechtel Power Corporation, has since determined that the j l

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failure of the switches could prevent the Containment Air Coolers and Hydrogen Mixing Fans from starting upon receiving an automatic

( actuation signal, thus resulting in a deficiency requiring a report per 10CFR50.55(e) .

2.0 DESCRIPTION

'0F SELECTOR SWITCH AND DEFICIENCY The Gould-Rundel 4-position selector switches are installed on the motor control centers for the purpose of providing a local means of operating the Containment Air Coolers and Hydrogen Mixing Fans.

The switch consists of a knob, head block unit, an operating unit, one or more contact blocks and an end plate. A shaft in the head block assembly engages a shaft coupling in the operating unit that in turn engages the first contact block mechanism via another shaft coupling. Successive shaft couplings in each contact block engage, in sequence, the next contact block.

Eight failed switches from the Callaway site were returned to the supplier (Gould) for analysis. Geuld reported that their examination of the failed switches revealed three possible failure modes: (1) Dirt accumulation on the contacts had rendered the contacts susceptible to arcing when they closed, (2) excessive force had been applied to the switch, shearing off the cams on the shaf t couplings in the contact blocks, rendering the switch position indeterminant and aggravating the problem of dirty f contacts, and (3) the design of the switch is such that, through sequential actuation of the contact blocks, the entire cam assembly

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on switches utilizing four or more contact blocks becomes susceptible to operating force-induced twisting, causing improper or delayed contact switching. (Note: The SNUPPS Switches are designed with 6 and 8 contact blocks.)

It is Bechtel's judgement that the underlying cause of the SNUPPS 4-position selector switch failures is design related, i.e.,

failure mode No. 3. Due to distortion of the long switch assembly i

during operation, proper contact making force was not applied. j Additional operating force was necessary to obtain the required electrical continuity. This force caused the switch cams to shear and the switch became non-functional. The SNUPPS Utilities concur with the Bechtel assessment of the failures.

3.0 SAFETY IMPLICATIONS The affected Gould-Rundel selector switches are used in the control circuits of the Callaway and Wolf Creek Containment Air Coolers'and the Hydrogen Mixing Fans. The design of the control circuit is such that proper operation of a contact block is required in order for these loads to start under automatic actuation.

Four Containment Air Coolers and four Hydrogen Mixing Fans are provided in the generic SNUPPS design. Failure to start of up to two air coolers and up to two mixing fans would have no safety impact since only two of each is required in order to perform i

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the intended safety functions. However it must be postulated that more than two Containment Air Coolers and/or more than two Hydrogen Mixing Fans may fail to start upon an accident signal due to the generic design deficiency described.

The loss of all 4 Hydrogen Mixing Fans is not a major concern following a LOCA. The fans serve only to enhance the uniform mixing of the containment atmosphere. The action of the containment sprays, the open design of the containment and the expected natural convection currents would ensure adequate mixing to preclude adverse concentrations of hydrogen to form in local areas.

The loss of all 4 Containment Air Coolers has not been specifically analyzed; however, the redundant and diverse containment spray system would provide pressure and temperature control for the containment atmosphere. A preliminary review of the heat removal l capability of the containment spray system acting alone indicates that the resultant containment pressure following a DBA would not likely exceed the containment design pressure of 60 PSIG. However, the resultant long-term containment temperature would, in all liklihood, exceed the maximum long-term qualified temperature profile of selected safety-related equipment needed to mitigate a DBA. Should this occur, operation of the required safety loads l

could not be assured during the long-term recovery period. On this basis, the defective switches are judged to have an adverse safety

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impact reportable under 10CFR50.55(e) criteria. Consequently, these items will be replaced with modified switches of a sound design.

4.0 RESOLUTION AND CORRECTIVE ACTION As indicated above, the MCC supplier will replace the affected switches with switches of a modified design. The new switches will be designed with a common steel shaft (in lieu of shaft couplings) running the length of the switch assembly. This will change the operation of the switch such that all contact blocks will be actuated simultaneously rather than sequentially. Thus the use of this steel shaft, resulting in the need to apply only a normal operating force to the switch mechanism, will assure proper switch operation, regardless of the additional contact blocks used. All replacement switches will be continuity tested and their design reviewed and confirmed at the time of changeout.

The new switches will be shipped to both sites and installed prior to fuel load. Direction and authorization to perform this rework has been furnished to each SNUPPS site and will be initiated upon receipt of the replacement switches.

The conclusion that the 4-position selector switches are susceptible to malfunction when utilizing an excessive number of contact blocks has caused concern as to whether other Gould switches used on the MCCs at either SNUPPS plant could be susceptible to similar malfunction. These switches are of the

2-position and 3-position design and contain up to 10 contact blocks. Although there have been no experienced failures of the 2-and 3-position switches to date, this matter is being pursued with Gould. If the 2- and 3-position switches are determined to be suseptible to similar malfunction, appropriate corrective actions will be taken and the NRC so advised.

The MCC supplier will be requested to inform othcr users of these 4-position selector switches of the problems experienced at Wolf Creek and Callaway so that corrective action can be taken if similar switches are found to be used in safety-grade nuclear systems.

5.0 CONCLUSION

S The SNUPPS Motor Control Centers supplying the Containment Air Coolers and Hydrogen Mixing Fans were found to have a selector switch of faulty design which, if left uncorrected, could potentially compromise the ability to maintain e.he station in a safe condition. The early detection and implementation of suitable l

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corrective action assures that these essential safety loads will l 1

function as designed and perform their intended safety function. I l

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