United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9508040285

     Commonwealth Edison
     1400 Opus Place
     Downers Grove, Illinois 60515

July 31, 1995

U.S. Nuclear Regulatory Commission
Washington, D.C. 20555

Attn.:  Document Control Desk

Subject:  ComEd 10 CFR Part 21 Final Report (File 94-12)
          Limitorque Actuator Potential Motor Pinion Key Failure

Reference:  I. Johnson (ComEd) letter to U.S. NRC, dated March 31, 1995

Attached to this letter is the final evaluation report on the concerns
initiated by Commonwealth Edison Company (ComEd) regarding the subject
Limitorque AISI Type 1018 motor pinion keys.

ComEd initially informed the NRC Staff that AISI Type 1018 keys may have
insufficient strength to withstand normal operating torques for the
entire MOV life in certain MOV Limitorque actuators.  After further
evaluation and testing of the AISI Type 1018 key under worst case
conditions, ComEd has determined that the AISI Type 1018 keys installed
at ComEd Nuclear facilities are qualified for plant life.

If there are any questions regarding this notification, please direct
them to Eric Steckhan at (708) 663-7437.

Respectfully,

Irene M. Johnson
Licensing Operations Director

Attachment: 10 CFR Part 21 Final Report

cc:  H.J. Miller, Regional Administrator - RIII
     R. Capra, Directorate III-2 Director, NRR
     R. Assa, Braidwood Project Manager, NRR

U.S. NRC                         - 2 -                 July 31, 1995

G. Dick, Byron Project Manager, NRR
C. Shiraki, Zion Project Manager, NRR
J. Stang, Dresden Project Manager, NRR
R. Pulsifer, Quad Cities Project Manager, NRR
W. Reckley, LaSalle County Project Manager, NRR
M. Kunowski, Resident Inspector - Braidwood

H. Peterson, Senior Resident Inspector - Byron
J. Roton, Senior Resident Inspector - Zion
M. Leach, Senior Resident Inspector - Dresden
C. Miller, Senior Resident Inspector - Quad Cities
P. Brochman, Senior Resident Inspector - LaSalle County
Office of Nuclear Facility Safety - IDNS

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            10 CFR Part 21 Final Evaluation Report-File 94-12
         Limitorque Actuator Potential Motor Pinion Key Failure

Applicability

This report is submitted in accordance with the requirements of 10 CFR
21, Section 21.21 (a).

Identification of Facility and Component

This report concerns AISI type 1018 motor pinion key failures for use in
Limitorque actuators on motor operated valves installed in safety-related
applications at all six ComEd nuclear stations.

Identification of Component Manufacturer

                    Limitorque Corporation
                    5114 Woodall Road
                    Lynchburg, Virginia 24506
                    Phone: (804) 845-9705

Nature of Defect

Failures of AISI type 1018 keys have occurred, which have been attributed
to insufficient material strength for certain Limitorque actuators.
Limitorque had previously notified the industry in 1983 that 4140 keys
are required in SMB-3, 4, and 5 actuators with 150 ft-lb. or larger
motors.  ComEd, along with KALSI Engineering, evaluated AISI type 1018
motor pinion key failures in SMB-0 and SMB-2 actuators.  Early results
from this evaluation indicated that key failure may occur at torque
levels below the published Limitorque actuator torque ratings (MATR).
During laboratory testing, KALSI failed 1018 keys three times
consecutively at approximately 200 cycles in a SMB-0 actuator with a 61.7
to 1 gear ratio and a 1800 rpm 40 ft-lb. motor.  This appears to be
inconsistent with industry failure data which involved higher speed
actuators (for example, higher key loads).

ComEd nuclear stations have not reported any incidents of failure of a
SMB-0 actuator resulting from a sheared motor pinion key.  One SMB-2
actuator failure was reported.  Dresden, Quad Cities, and Zion Nuclear
Stations all have SMB-0 actuators which have been operated in excess of
200 cycles, which is the reported failure cycles at KALSI, without
incident.

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            10 CFR Part 21 Final Evaluation Report-File 94-12
         Limitorque Actuator Potential Motor Pinion Key Failure

Evaluation Results

ComEd completed and evaluation of this issue with the following results:

     o    AISI Type 1018 keys are qualified for use in Limitorque
          actuators with the exceptions noted by Limitorque.

     o    Motor pinion keys should be installed in accordance with
          Limitorque Guidelines provided in Maintenance Update 89-01.

These results are based on the following:

1.   ComEd successfully completed four tests at greater than 120% of the
     torque rating for a SMB-0 Actuator.

     o    All tests exceeded 2000 cycles.
     o    Two tests exceeded 5000 cycles with the KALSI motor and overall
          actuator ratio (OAR).
     o    Two tests completed 4000 cycles and 3/8" of the key not
          engaged.
     o    No Key Failures.

2.   The key material used during ComEd testing had a lower strength than
     the keys used at KALSI and are representative of typical AISI Type
     1018 keys.

3.   Shear and bearing stresses at the key are significantly below
     allowable stresses for all ComEd GL 89-10 MOV's.

Time of Discovery

On September 13, 1994, an evaluation was initiated for Part 21
reportability.

Corrective Actions

ComEd has issued guidelines to its six nuclear stations on the methods
for properly installing motor pinion keys.

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            10 CFR Part 21 Final Evaluation Report-File 94-12
         Limitorque Actuator Potential Motor Pinion Key Failure

Number and Location of Potentially Defective Components

Each of ComEd's six nuclear stations have between 50-100 safety-related
SMB-0, SMB-1, and SMB-2 actuators.

Contacts

Questions pertaining to this notification should be addressed to:

Eric S. Steckhan
Nuclear Engineering Services
ComEd
1400 Opus Place, Suite 400
Downers Grove, IL 60515.
(708) 663-7437

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