ML20149M097

Final Deficiency Rept 213 Re High Acceleration Values for PSA-10 Snubbers.Initially Reported on 870819.All Snubber Installations That Use Size PSA-10 Snubbers Identified & Snubbers Mfg After June 1985 Will Be Installed

ML20149M097
Person / Time
Site:	Limerick
Issue date:	09/18/1987
From:	Kowalski S PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	Russell W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
213, NUDOCS 8802250317
Download: ML20149M097 (4)

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l PHILADELPhl A ELECTRIC COM PANY 2301 M ARKET STREET P.O. BOX 8699

? HILADELPHI A. PA.19101 1215) 84 t 4 502 S. J. KoW AL5KI V1C E PRE $1OE!1Y SEP 18 387 Mr. W. T. Russell, Administrator j U.S. Nuclear Regulatory Ccmniulco, Region ! l Attention: Doctinent Control Desk Washington, DC 20555 Docket No. 50-353

Subject:

Limerick Generating Station Unit 2 l Significant Deficiency Evaluation No. 213-2 Pacific Scientific Mechanical Shock Suppressors with High Acceleration Values l 1

Reference:

Telecon, P. K. Pav11 des to H. Williams (USNRC),

dated August 19, 1987 Flie: QUAL 2-10-2 SDR No. 213

Dear Mr. Russell:

In ccnpliance with 10CFR$0.55Ce), we are submitting our final Significant Deficiency Report concerning the subject high acceleration values for PSA-10 size snubbers.

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

Sincerely, l

iWi/pdO9088707 l Copy to: Mr. W. T. Russell, Administrator U.S. Nuclear Regulatory Ccnmission, Region 1 631 Park Ave.

King of Prussia, PA 19406 Mr. E. M. Kelly, Senior Resident inspector S. Nuc e r Regulatory Conmission Sanatoga, PA 19464 8002250317 870918 l 1 i

PDR ADOCK 05000353 .m S- - . D C.D I L' ,

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PHILADELPHIA ELECTRIC CCPPANY MECHANICAL ENGINEERING DIVISION h2 2301 Market Street SIGNIFICANT DEFICIENCY EVALUATION - SDR to. 213-2 PACIFIC SCIENTIFIC MECHANICAL SHOCK SUPPRESSORS LIMERICK GENERATING STATION UNIT 2 NRC CONSTRUCTION PERMIT NO. CPPR-107 DOCKET NO.50-353 INTRODUCTION:

This significant deficiency evaluation provides InforTnation on Pacific Scientific mechanical shock suppressors (snubbers), size PSA-10, for which test results show.activatim acceleration values greater than the manufacturers design limit (0.02g). The cause of these high acceleration values is excessive greasing of internal conponents. In the case of an earthquake or other design basis dynamic event snubbers are called upon to Ilmit piping and component displacement and thereby mitigate the consequences of the event.

This deficiency was reported via telecon to H. Williams, USNRC Region I, by P. K. Pav1fdes on August 19, 1987.

BACKGROUto:

Pacific Scientific snubbers are designed to limit the acceleration of piping and attached ccrnponents to less than 0.02g. Acceleration values in excess of 0.02g are acceptable where Justified by a case specific analysis. If a dynanic event accelerates a pipe or canponent, a restraining force Is applied by the snubber which limits the acceleration to less than 0.02g. The snubber's perfonnance is independent of the amount of force being applied and at no time does it lock and beccme a rigid structural ment >er. Another aspect of snubber design is that slow trovements, such as thermal expansion, are not inhibited.

The operation of the snubber is performed by the interaction of telescoping and rotating ccnvenents. Two non-rotating telescoping tubes connect the pipe or other conponent to a fixed structure.

Inside these tubes is a ball screw and nut which convert the linear telescoping motion to rotation of the ball screw and drum asserrbly.

The drtm assent >1y is coupled to an inertia mass via a capstan spring.

When a dynamic event occurs in excess of 0.02g the ball screw and drun begin to accelerate the inertla mass. The difference in relative angular acceleration causes a clutch spring that is attached to the Inertla mass to contact the capstan spring. This causes the capstan s;ving to tighten around a mandrel which is part of one of the structural tubes. This tightening induces a rotaticnal restraining force to be applisd to the ball screw which in turn restricts the linear notion of the telescoping tubes.

t CORRECTIVE ACTIONS:

Pacific Scientific has inforned PECo that they at one time did apply grease to specific snubber internals in order to reduce break away frictional force. They subsequently disccvered that heat, radiation and time will degrade the lubricant which In turn causes an increase in snubber break away and drag force. It is for the above reasons that Pacific Scientific discontinued the use of grease in the capstan spring area after June 1985.

PECo has identified all snubber Installations that use size PSA-10 snubbers and alll install those snubbers manufactured after June of 1985.

Due to the availability cf PSA-10 snubbers during the course of ccnstruct!on for Limerick Unit 2, if it beccmes necessary to install snubbers manufactured prior to June 1985, then only those snubbers with acceptable functional test results will be used.

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o Because the snubber rotating parts are synmetrical and unaffect.eu by the direction of rotation,.the above principles of operation. apply to the snubber in both tension and conpression.

During thermal movement, because the acceleration is much less than the threshold value of 0.02g, the Inertia mass moves slowly and does not tighten the capstan spring; therefore, no restraining force is applied by the snobber.

DESCRIPTION OF DEFICIENCY:

During-recent Technical Specification surveillance testing of Limerick Unit I snubbers approximately 30% of all size PSA-10 sntbbers that were tested were found to have acceleration values greater than 0.02g. Testing of all Unit 1 snubbers that required functional examination was perforTned by Wyle Laboratories personnel using a Wyle Laboratories Model 150 snubber test machine.

All PSA-10 snubbers with test results that exceeded the established acceptance criteria were disassenbled, inspected to determine the cause of the exceedance, and rebuilt. For the specific case of high acceleration It was determined that an excessive amount of grease was applied to Internal conponents. The excess grease was reoved from the snubber and they were re-asscrrbled and re-tested. l With the exception of 5 PSA-10 snubbers, all test results showed a drastic reduction in acceleration values. Mcwever, acceleration values for these 5 snubbers could not be reduced to less than 0.02g with degreasing alone and the final solution was to replace the clutch spring and capstan spring on each snubber with newer designed parts j frcm Pacific Scientific. Subsequent testing showed that the replacement '

parts lowered acceleration values to less than 0.02g.

Because of the identified deficiency encountered during Unit 1 testing, the corrective actions described below have been impimented for Limerick Unit 2.

ANALYSIS OF SAFETY IMPLICATIONS:

High activation acceleration values for PSA-10 snubbers represents a condition that may reduce the availability of safety related systems. High acceleration snubbers can cause failure of sensitive eculpment by allowing larger piping / equipment displacements than were originally accepted. These displacements could affect the operability of the sensitive ccmponents and possibly render a system inoperable. Since Limerick Unit 2 is under construction the Irroact of these safety inplications is minimal .

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