United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 82-01: Auxiliary Feedwater Pump Lockout Resulting from Westinghouse W-2 Switch Circuit Modification

                                                            SSINS:  6835 
                                                            Accession No.: 
                                                            8107230043 
                                                            IN 82-01 

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C.  20555

                              January 22, 1982

Information Notice No. 82-01:  AUXILIARY FEEDWATER PUMP LOCKOUT RESULTING
                                  FROM WESTINGHOUSE W-2 SWITCH CIRCUIT 
                                  MODIFICATION 

Description of Circumstances: 

On September 14, 1981, Commonwealth Edison's Zion Unit 2 was conducting a 
normal plant cooldown to begin a refueling outage.  The reactor coolant 
system was operating at 350 psig and 250oF.  Both residual heat removal 
(RHR) systems were operating to remove decay heat and control reactor 
coolant system temperature.  Steam generator water levels dropped below the 
10% low level auxiliary feedwater (AFW) pump auto-start setpoint, and the 
motor-driven AFW pumps activated as designed.  The operator placed the 
control switched in the pull-to-lock-out position to stop the AFW pumps.  
Later, to control the rate of plant cooldown, the operator tried to increase 
the cooldown rate by feeding water to the steam generators.  The AFW pumps 
would not restart on command. The power supply circuit breaker for one of 
the pumps was momentarily racked out to the disconnect position and then 
racked back in for service.  As result of this procedure, the AFW pump 
restarted.  No further problems were encountered during the plant cooldown 
operation. 

Investigation into the problem revealed that the licensee's modification to 
the Westinghouse W-2 control switch used with the AFW pumps differed from 
that recommended in IE Bulletin 80-20 (IEB).  IEB 80-20, entitle "Failures 
of Westinghouse Type W-2 Spring Return to Neutral Control Switches," 
recommended using only the existing green status light to provide early 
detection of an open circuit caused by a neutral position (auto-start) 
contact failure of the control switch.  However, in this application, the 
licensee's modification included both the red and green status lights.  This 
resulted in a sneak circuit path which prevented AFW pump restart under 
certain circumstances. 

Following an auto-start of the AFW pump and the subsequent securing of that 
pump by placing the control switch in the pull-to-lock-out position, the 
licensee found that a live continuous circuit existed between the red light 
and the anti-pump coil.  This sneak current path prevented deenergization of
the anti-pump coil (circuit reset) that is necessary for pump restart. 

The licensee reports that, following the initial circuit modification, the 
sneak path was noted to cause the red indicating light to glow only dimly 
when the control switch was placed in the pull-to-lock-out or trip positions 
(see Figures 1 though 3 and Table 1).  However, the sneak path was not fully
analyzed at that time, and no detailed function testing of the modified 
.

                                                            IN 82-01 
                                                            January 22, 1982
                                                            Page 2 of 2 

circuit was performed.  Note that when the red light is used to indicate 
"pump on," as in this application, the light should not go on when the 
control switch has been placed in either the pull-to-lock-out or trip 
positions. 

Circuit modifications may have been made at various plants in response to 
information in IEB 80-20.  These modifications, where different from IEB 
80-20 recommendations, may have caused sneak paths with various degrees of 
impact that may not have been detected by previous engineering analysis or 
post-installation testing. 

This information notice is provided as an early notification of a 
potentially significant matter.  It is expected that recipients will review 
the information for applicability to their facilities.  No specific action 
or response is required at this time.  If you have any questions regarding 
this matter, please contact the Regional Administrator of the appropriate 
NRC Regional Office. 

Attachments:
1.  Figures 1, 2 and 3
2.  Recently issued IE Information Notices

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