United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 88-42: Circuit Breaker Failures due to Loose Charging Spring Motor Mounting Bolts

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                      OFFICE OF NUCLEAR REACTOR REGULATION
                             WASHINGTON, D.C.  20555

                                  June 23, 1988


Information Notice No. 88-42:  CIRCUIT BREAKER FAILURES DUE TO LOOSE 
                                   CHARGING SPRING MOTOR MOUNTING BOLTS


Addressees:

All holders of operating licenses or construction permits for nuclear power 
reactors.

Purpose:

Information Notice No. 87-41, "Failures of Certain Brown Boveri Electric 
Circuit Breakers" was issued August 31, 1987.  This information notice is 
being provided to alert recipients of additional information regarding circuit 
breaker failures due to loose charging spring motor mounting bolts.  It is 
expected that recipients will review the information for applicability to 
their facilities and consider actions, as appropriate, to avoid similar 
problems.  However, suggestions contained in this information notice do not 
constitute NRC requirements; therefore, no specific action or written response 
is required.  

Description of Circumstances:

There are two emergency diesel generators (EDGs) at North Anna Unit 2 ("H" and 
"J").  On May 18, 1988, with the unit at power, the licensee removed the "J" 
EDG from service for scheduled preventive maintenance.  On May 19, 1988, fol-
lowing completion of the scheduled preventive maintenance, the "J" EDG failed 
to pick up and carry the required load during preoperational testing.  The 
licensee then shut down the "J" EDG and performed unplanned corrective mainte-
nance.  The licensee's technical specifications require that the operable EDG 
be tested within 24 hours if the inoperable EDG is inoperable due to any cause 
other than preplanned preventive maintenance or testing; thus, because of the 
unplanned maintenance on the "J" EDG the licensee tested the "H" EDG.  During 
this test, the "H" EDG output circuit breaker (ITE Type 5HK) failed to close.  
The licensee's investigation determined that the "H" EDG output breaker 
closing spring had not been charged because the charging spring motor mounting 
bolts had become loose, allowing the motor to become detached from the frame.  
The output breaker for the "H" EDG had been successfully closed on May 6, 
1988; however, procedures did not require verification that the closing spring 
had successfully charged.  Thus, both EDGs were inoperable for approximately 
38 hours.

A similar occurrence was previously reported in accordance with the 
requirements of 10 CFR 50.55(e) by Philadelphia Electric Company (the Limerick 
Units 1 and 2 licensee) on August 27, 1984.  During an EDG preoperational 
test, the charging 


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spring motor of a BBC Brown Boveri, Inc. 5HK breaker failed to perform its 
intended function.  The licensee determined that three out of the four hori-
zontal charging spring motor mounting bolts had loosened, allowing the 
charging spring motor to rotate.  Subsequent inspections identified a similar 
breaker with loose charging spring motor mounting bolts.  The licensee 
indicated that the charging spring motor mounting bolts had not been 
sufficiently torqued by the vendor (e.g., measured torque values were 3 to 4 
foot-pounds).  Although the vendor recommends inspections of all accessible 
bolts after 1000 breaker operations, the breaker failure occurred after only 
several hundred operations.  The licensee indicated that charging spring motor 
mounting bolts in similar breakers would be removed, cleaned, coated with 
Locktite, and torqued to 12 foot-pounds.

Discussion:

Failure of a circuit breaker to perform its intended function can result in 
the loss of a power supply (such as a vital bus or an EDG).  The occurrence of 
these events, including the event at River Bend previously discussed in 
Information Notice 87-41, indicates that loose charging spring motor mounting 
bolts may be a generic concern.  In addition, because of changes in corporate 
name, mergers, etc., circuit breakers similar to those discussed above may 
indicate manufacture by ITE, ITE Imperial, Gould, Brown Boveri, or a 
combination thereof.  Recipients may need to be cognizant of this when 
determining whether they utilize similar equipment.

No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical 
contact listed below or the Regional Administrator of the appropriate regional 
office.  




                              Charles E. Rossi, Director
                              Division of Operational Events Assessment
                              Office of Nuclear Reactor Regulation

Technical Contact:  Jack Ramsey, NRR
                    (301) 492-1167

Attachment:  List of Recently Issued NRC Information Notices
.                                                            Attachment
                                                            IN 88-42 
                                                            June 23, 1988 
                                                            Page 1 of 1

                             LIST OF RECENTLY ISSUED
                            NRC INFORMATION NOTICES 
_____________________________________________________________________________
Information                                  Date of 
Notice No._____Subject_______________________Issuance_______Issued to________

88-41          Physical Protection           6/22/88        All holders of OLs
               Weaknesses Identified                        or CPs for nuclear
               Through Regulatory Ef-                       power reactors. 
               fectiveness Reviews (RERs) 

88-40          Examiners' Handbook for       6/22/88        All holders of OLs
               Developing Operator                          or CPs for nuclear
               Licensing Examinations                       power reactors. 

88-39          LaSalle Unit 2 Loss of        6/15/88        All holders of OLs
               Recirculation Pumps With                     or CPs for BWRs. 
               Power Oscillation Event 

88-38          Failure of Undervoltage       6/15/88        All holders of OLs
               Trip Attachment on General                   or CPs for nuclear
               Electric Circuit Breakers                    power reactors. 

88-37          Flow Blockage of Cooling      6/14/88        All holders of OLs
               Water to Safety System                       or CPs for nuclear
               Components                                   power reactors. 

88-36          Possible Sudden Loss of RCS   6/8/88         All holders of OLs
               Inventory During Low Coolant                 or CPs for PWRs. 
               Level Operation                              

88-35          Inadequate Licensee Performed 6/3/88         All holders of OLs
               Vendor Audits                                or CPs for nuclear
                                                            power reactors. 

88-34          Nuclear Material Control      5/31/88        All holders of OLs
               and Accountability of                        or CPs for nuclear
               Non-Fuel Special Nuclear                     power reactors. 
               Material at Power Reactors 

87-61,         Failure of Westinghouse       5/31/88        All holders of OLs
Supplement 1   W-2-Type Circuit Breaker                     or CPs for nuclear
               Cell Switches                                power reactors. 
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit 
Page Last Reviewed/Updated Tuesday, November 12, 2013