United States Nuclear Regulatory Commission - Protecting People and the Environment

IE Circular No. 81-13, Torque Switch Electrical Bypass Circuit for Safeguard Service Valve Motors

                                                          SSINS No.: 6830  
                                                          Accession No.:   
                                                          IEC 81-13        

                               UNITED STATES 
                           WASHINGTON, D.C. 20555 
                             September 25, 1981 

                         SAFEGUARD SERVICE VALVE MOTORS 


A common wiring discrepancy between the as-designed and as-installed valve 
motor control circuitry caused, at least in part, a valve malfunction at two
operating boiling water reactors. In each case, an electrical bypass circuit
around the valve-open torque switch on a Limitorque valve operator was not 
installed as designed. The intent of this bypass feature is to override the 
valve-open or valve-close torque switch circuits to ensure that full motor 
torque is applied to the valve until it is near full open or full closed. 
This is to eliminate the chance of the valve stalling out under emergency 
conditions before it has completed its travel. 

Description of Circumstances: 

Brunswick Unit 2 - During a test of the reactor core isolation cooling 
(RCIC) system at this facility, in March 1978, the injection valve would not 
open. The valve and valve motor were checked, cycled and tested; no problems 
were identified. In September 1980, following a reactor scram, the same 
valve failed to fully open. An inspection of the valve motor control 
circuitry by the licensee revealed that the electrical bypass circuit wiring 
around the valve-open torque switch was not installed as designed. 
Examination of other RCIC system valves revealed that four of ten similar 
torque switch bypass circuits had not been installed. The missing electrical 
bypasses were installed. 

Cooper Station - During a test of the residual heat removal (RHR) system at 
this facility, in December 1980, one of the RHR loop injection line 
isolation valves would not open. The problem was reported to be an incorrect 
closing torque switch setting. However, it was noted and reported, as 
unrelated to this event, that both Train A and Train B injection valve-open 
torque switch bypass circuits had not been installed in the valve motor 
control circuitry as designed. This discrepancy was corrected. 

Recommended Action for Holders of Operating Licenses or Construction 

1.   Verify that all valves important to safety, which are required by the 
     design to have torque switch bypass circuits installed, do in fact have
     these circuits installed. 

2.   Verify that all applicable electrical drawings correctly reflect these 
     electrical bypass circuits. 


                                                      IEC 81-13           
                                                      September 25, 1981  
                                                      Page 2 of 2         

3.   If inspection reveals that required bypass circuits are not installed, 
     installation should be initiated as soon as practicable after the need 
     has been determined. 

4.   Establish controls to assure that torque switch bypass circuits are not
     inadvertently removed and that they are restored if they are removed 
     for maintenance or test. 

No written response to this circular is required; however, if discrepancies 
are found, a report may be required by applicable Technical Specifications 
or other NRC reporting requirements. If you need additional information with
regard to this subject, please contact the Director of the appropriate NRC 
Regional Office. 

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