Information Notice No. 84-13:Potential Deficiency in Motor-Operated Valve Control Circuits and Annunciation
SSINS No.: 6835 IN 84-13 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 February 28, 1984 Information Notice No. 84-13: POTENTIAL DEFICIENCY IN MOTOR-OPERATED VALVE CONTROL CIRCUITS AND ANNUNCIATION Addressees: All holders of a nuclear power reactor operating license (OL) or construction permit (CP). Purpose: This information notice is provided to alert licensees to a specific design in the circuitry used for control and annunciation of certain safety-related electric motor-operated valves (MOVs). This design may, under thermal overload (TOL) bypass condition, preclude timely detection of a failure of a safety-related motor. Affected licensees may elect to modify their design to provide continuous TOL trip annunciation and indication. No specific action or response to this notice is required. Description of Circumstances: On September 2, 1983, Pennsylvania Power and Light Company's (PP&L's) Susquehanna Steam Electric Station reported a condition related to a failed MOV which supplies cooling water to the barometric condenser of the high pressure coolant injection (HPCI) turbine and to the HPCI lube oil cooler pump. The TOL had tripped when the valve torque switch malfunctioned. This condition was not indicated or annunciated to the control room operator. Investigation into the valve failure found a burned out electric motor. This condition went undetected for approximately three weeks. PP&L identified seven previous MOV failures involving overloads, electric motors, and/or valve torque switches. The present control circuit design at Susquehanna does not annunciate a motor overload condition or a burned out motor if the key lock bypass switch is in a "bypass" position. The purpose of the bypass feature around the TOL device is to avoid spurious trips of MOVs under accident demand situations. One of the positions in Regulatory Guide 1.106 is that the TOL should not preclude completion of the safety function. At Susquehanna, the key lock bypass switch is normally kept in the bypass position. This continuous bypass of the TOL during normal operation is one means of complying with Regulatory Guide 1.106 since a tripped TOL will not inhibit operation of the MOV. 8401190072 . IN 84-13 February 28, 1984 Page 2 of 2 However, with the Susquehanna design, with the key lock in the bypass position, there is no indication of a tripped TOL. In such designs, emphasis is placed on assuring operability of the safety function rather than on protecting individual components from damage. However, good engineering practice would retain the TOL protection for normal or test functions of the MOV. Such a design would permit the TOL protection for the motor to be reinstated under test conditions. Corrective Action Taken by Licensee: 1. Following the discovery of this situation, PP&L inspected all AC and DC motors of the MOVs and found them satisfactory. 2. Shift supervisors were instructed that the key lock bypass switch should remain in the "open" (test) position for at least thirty (30) seconds following a valve closing operation, before the switch was placed back to the "normal" (bypass) position. This would assure indication in the control room if the overload relay actuated to protect the motor of the MOV against a TOL condition. 3. As an interim measure PP&L implemented a surveillance testing program, and is presently evaluating the bypass circuit design and possible changes to provide for continuous annunciation and indication of TOL trip conditions. Other licensees may elect to provide similar capability. If you have any questions regarding this matter, please contact the Regional Administrator of the appropriate NRC Regional Office, or this office. Edward L. Jordan, Director Division of Emergency Preparedness and Engineering Response Office of Inspection and Enforcement Technical Contact: W. Laudan, IE (301) 492-9759 Attachment: List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021