ML20238A212

Significant Deficiency Evaluation Rept 209 Re Limitorque Motor Operators W/Hydraulic Locking.Initially Reported on 870626.Limitorque Motor Operators Being Processed Through Rework Program.Item Not Reportable Per 10CFR50.55(e)

ML20238A212
Person / Time
Site:	Limerick
Issue date:	08/24/1987
From:	Kowalski S PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	Russell W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
209, NUDOCS 8708280362
Download: ML20238A212 (4)

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PHILADELPHIA A ELECTRIC COM PANY 2301 MARKET STREET P.O. BOX 8699 PHILADELPHIA A, PA.19101 1215) 841 45o 2

s. J. KoWALSKI VIC E-P R E hiD E N T a waim a s RING AND R$$$ ARCH AUG 241987 Mr. W. T. Russell, Administrator U. S. Nuclear Regulatory Commission, Region I Attentioni Document Control Desk washington, DC 20555

SUBJECT:

Significant Deficiency Evaluation No. 209 Limitorque Motor Operators with Hydraulic Locking Limerick Generating Station, Unit 2 NRC Construction Permit No. CPPR-107 FILE:

QUAL 2-10-2 SDR No. 209 REF:

1) Telecon, P. K. Pavlides, PECo to Sam Cellins, USNRC dated 6/26/87

2) Telecon, J. P. Evans, PECo to Sam Collins, USNRC dated 7/28/87 3 ) Telecon, W. J. Boyer, Jr., PECo to Sam Collins, USNRC dated 8/6/87

Dear Mr. Russell:

l We have completed our evaluation of the condition verbally reported to you as a significant deficiency on June 26, 1987, and conclude that it is not reportable under the requirements of 10CFR50.55 (e). The attached memorandum documents our evaluation of this deficiency.

We are sorry for the delay in furnishing the written response to our initial notification.

We trust that this satisfactorily resolves this item. If further information is required, please do not hesitate to contact us.

SI"C'#'lY 8708280362 870824 PDR ADDCK 05000353 h

S PDR Attachment Copy tot W. T. Russell, Administrator U. S. Nuclear Regulatory Commission, Region 1 631 Park Ave.

King of Prussia, PA 19406 I

E. M. Kelly, Senior Resident Inspector U. S. Nuclear Regulatory Commission i

P. O. Box 46 Sanatoga, PA 19464

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ELECTRICAL ENGINEERING DIVISION J

N3-1, 2301 Market Street I

Significant Deficiency Evaluation - SDR No. 209 Limitorque Valve Motor Operators Limerick Generating Station, Unit 2 NRC Construction Permit No. CPPR-107

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INTRODUCTION:

This Significant Deficiency Evaluation provides information on hydraulic locking associated with Limitorque type SMB motor operators.

These operators are used on a large number of safety related valves at Limerick Generating Station Unit 2.

In the case of an accident, these valves would be called on to open or close to mitigate the accident.

This was previously reported as a significant deficiency via tele-con to S. Collins, USNRC Region I, by P. K. Pavlides on June 26, 1987.

After further evaluation, Philadelphia Electric Company (PECo) has con-cluded that this deficiency is not reportable under the requirements of 10CFR50.55 (e).

BACKGROUND Limitorque operator control circuits use a torque switch to limit the output torque / thrust of the operator. The torque switch limits cperator output torque / thrust by sensing the compression of a spring inside the operator. This spring is commonly called a spring pack. The spring pack consists of a set of Belleville washers stacked on a common shaft. At the ends of the Belleville washer stack are two flat thrust washers. Surrounding the Belleville washers is a cylinder called a torque limiting sleeve. The spring pack is located in a cavity ma-chined in the operator housing and held by the spring cartridge cap.

When the valve is seated or a mechanical overload occurs, the spring pack is com. pressed a distance proportional to the output torque of the operator. The torque switch operates when the spring pack is com-pressed a preset distance as determined by the torque switch setting.

DESCRIPTION OF DEFICIENCY:

During the startup of Limerick Unit 1, the torque switch on sever-al motor operators failed to operate during valve closure. This caused the motor to stall and trip on operation of the thermal overload -

i device. An investigation concluded that grease in the spring pack l

cavity in conjunction with other factors prevented sufficient spring j

pack compression to actuate the torque switch.

This is commonly called i

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" hydraulic lock".

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4 DESCRIPTION OF DEFICIENCY - Con't.

Normally, during spring pack compression, any grease in the spring pack cavity is expelled to the main housing or spring cartridge cap If the grease cannot escape from the spring pack cavity, area.

hydraulic lock occurs. This appears to be related to the following j

The torq. limiting sleeve is in a position whereby it re-stricta the flow of grease from the spring pack area to the main housing or spring cartridge cap area.

1 The spring pack compression rate is greater 2.han the rate at which grease csn be expelled from the spring pack cavity.

The sprir.g pack cavity is easily filled by a high grease level in the operator housings ANALfGIS OF SAFETY IMPLICATIONS:

Hydraulic locking of a Limitorque motor operator represents a con-dition that may reduce the availability of safety related systems.

Hy-draulic locking can cause valve motor operator failure whenever the thermal overload device is bypassed (e.g., during automatic actuation).

Failure would make the valve inoperable and, depending on valve posi-tion and operability requirements, possibly render a system or train inoperable. However, valve motor operator failures due to hydraulic locking occur infrequently and sporadically, hence on a random basis.

No mechanism har been identified which would cause valves in redundant trains or systems to hydraulically lock during the short time required

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for operability following en accident. For this reason, PECo concludes f

that hydraulic locking does not present a subtantial safety hazard.

With respect to normal operating conditions, it should be noted that Limerick is provided with annunciation of thermal overload opera-tion at all times to provide prompt indication of an overload condition.

CORRECTIVE LCTIONS:

All of the Limerick Unit 2 Limitorque me.or operators are being processed through the Limerick Limitorque Rework Program. As part of this program, two clots ar6 being machined at each end of the torque limiting sleeve. These slota provide additional area through,which grease can escape from the spring pack cavity to the main housing or i

spring cartridge cap area during spring pack compression. Limitorque has evaluated th6 addition of the slots and concluded that they will have no detrimental effects en the motor operator or its operation.

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CORRECTIVE ACTIONS - Con't.

Limitorque has advised PECo that they are investigating this prob-lem further. They may be taking actions in addition to previous changes to preclude this problem in the manufacturing process.

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