United States Nuclear Regulatory Commission - Protecting People and the Environment

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. 




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                                                        IN 84-13           
                                                        February 28, 1984  
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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 

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