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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 k:\n1a\dresden\9412p21.wpf:2 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. k:\n1a\dresden\9412p21.wpf:3 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. k:\n1a\dresden\9412p21.wpf:4 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 k:\n1a\dresden\9412p21.wpf:5 *** END OF DOCUMENT ***