ML17312A678

Forwards Engineering Evaluaion Rept of MOV Key Failures Which Represent Potential common-mode Failure Mechanism for Associated safety-related Sys

ML17312A678
Person / Time
Site:	Palo Verde
Issue date:	03/29/1996
From:	Rossi C NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD)
To:	Gillespie F, Thadani A, Zimmerman R NRC (Affiliation Not Assigned)
Shared Package
ML17312A680	List: ML17312A678 ML17312A681
References
NUDOCS 9604160252
Download: ML17312A678 (6)

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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 March 29, 1996 MEMORANDUM TO:

FROM'UBJECT:

Frank P. Gillespie, Director, DISP:NRR Ashok C. Thadani, Director, ADTR:NRR Roy P.

Zimmerman, Director, ADP:NRR Gary M. Holahan, Director, DSSA:NRR Brian W. Sheron,

Director, DE:NRR Dennis M. Crutchfield, Director, DRPM:NRR Bruce A. Boger, Director, ORCH:NRR Lawrence C. Shao, Director, DET:RES M. Wayne Hodges, Director, DST:RES Bill M. Morris, Director, DRA:RES James T. Wiggins, Director, DRS:RGN-I Albert F. Gibson, Director, DRS:RGN-II Geoffrey E. Grant, Director, DRS:RGN-III Thomas P.

Gwynn, Director, DRS:RGN-IV Charles E. Rossi, Direct Safety Programs Division Office for Analysis and Evaluation of Operational Data MOTOR-OPERATED VALVE KEY FAILURES Attached is an engineering evaluation report of motor-operated valve (MOV) key failures.

This study was initiated following several occurrences of motor pinion key failures at Palo Verde Unit 1 which were reported as a Licensee Event Report (LER) in April 1995.

The key failures were not detected during surveillance testing but were discovered in several separate maintenance activities.

The key failures represent a potential common-mode failure mechanism for the associated safety-related systems.

A significant number of MOV key failures which involved anti-rotation

keys, valve operator-to-valve stem keys, and motor pinion gear keys have been identified.. Many of these key failures were not detected during surveillance tests but were detected on demand, during valve operations, or during maintenance activities and had existed for some time before they were discovered.

The dominant attributed cause of these key failures was key loosening associated with setscrew loosening or improper staking.

In addition to key loosening, high impact loads and improper material were also major contributors to motor pinion key failures.

The pinion key failures attributable to high impact loads or improper material appear to involve AISI type 1018 keys in high speed and high inertia configurations.

CONTACT:

Chuck Hsu AEON/SPD/m (301) 415-6356 9604f60252 960329',

PDR ADQCK 05000528 P

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F. Gillespie, et al.

The replacement of 1018 keys with harder 4140 keys, in some cases, ma lead to keyway deformation or damage, depending on impact loads and the sha material.

The situation may present a complex stress problem tha is not completely considered in design and could produce a severe and c

plex stress concentration on the key as well as the keyway.

This could le to cracking and failure of the shaft.

In view of the potential for these key problems to render afety systems inoperable, additional emphasis should be placed on ens ing that industry personnel responsible for valve maintenance and design and NRC inspection personnel are aware of the problems which have occurr d.

The attached engineering evaluation report delineates the follow ng:

(1)

The importance of plant maintenance rograms to verify that MOV keys are staked and secured as req red.

(2)

The importance of plant MOV sur illance and maintenance activities to assure the early detection of key degradation.

(3)

The possibility of shaft cr cking as a result of replacement of 1018 keys with harder mat ial when the replacement will involve a

relatively soft shaft a

high impact loads.

We would like to discuss with yo how the information in the attached report can be used to reduce the numbe of problems caused by MOV key failures in the future.

Attachment:

As stated cc w/att:

V. K. Chexal, EPRI Pat Lewis, INPO Debbie W. gueener, OAC Distribution w Public Central File RAB R/F SPD R/F t:

EJordan DRoss FCongel DHickman PBaranowsky KRaglin

AChaffee, NRR

RWessman, NRR MMayfiel d, RES

REmrit, RES

RSavio, ACRS

LSoffer, EDO D

CUMENT NAME:

C: iWP5liWPDOCSiEEMEMKEY.CCH; C; 'ItWP5ltt,WPDOCSiEEKEY. CCH See previous concurrence:

o receive a copy of this document, Indicate In the box:

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D:SPD NAME DATE 01/26/96*

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