Information Notice No. 93-26: Grease Solidification Causes Molded-Case Circuit Breaker Failure to Close

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

                                 April 7, 1993


NRC INFORMATION NOTICE 93-26:  GREASE SOLIDIFICATION CAUSES MOLDED CASE        
                               CIRCUIT BREAKER FAILURE TO CLOSE                
             

Addressees

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

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to a problem with a 400-amp frame, 600 Vac molded
case circuit breaker manufactured by General Electric Corporation (GE)
(Part No. TJK436Y400) which failed to close when required due to grease
solidification.  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 are not NRC requirements; therefore, no specific action or written
response is required.

Description of Circumstances

On March 26, 1992, an engineered safety feature actuated at the Nine Mile
Point Nuclear Station Unit 2 because of the loss of output power from an
uninterruptible power supply (UPS) while the loads were being transferred from
UPS power to the maintenance supply power.  During the transfer, the
maintenance supply output circuit breaker (CB-4) failed to close causing a
loss of power to the standby gas treatment system radiation monitoring
cabinet, a false-high radiation signal, a group 9 primary containment
isolation, the loss of a control room fire panel annunciator, and a loss of
communication between the radiation monitoring system computer and non-Class
1E radiation monitors.  The operator immediately took corrective action to
manually close circuit breaker CB-4 and restore the UPS loads.  The UPS loads
lost power for approximately 12 minutes during the event.

Discussion

Niagara Mohawk Power Corporation, the licensee for Nine Mile Point 2,
determined that the cause of the failure of circuit breaker CB-4 to close was
that the grease used at the pivot points inside the breaker had dried out and
solidified.  When the grease dried out, it caused increasing friction and
gouging at the metal-to-metal contact areas.  This friction caused the breaker
to become increasingly more difficult to close, until, finally, the breaker
would not close at all.  The licensee located all breakers of the same make,
model, and year as the one that failed and scheduled their replacement.

9304010146
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                                                            IN 93-26
                                                            April 7, 1993
                                                            Page 2 of 2


GE has stated that all molded case circuit breakers manufactured prior to 1985
used a soap-based or clay-based grease that could solidify with age, and that
they recommend field testing to identify such solidification.  Since 1985, GE
has replaced the soap-based and clay-based grease with a synthetic grease that
does not dry out and solidify with age.  However, it is possible that the
older molded case circuit breakers using the clay-based and soap-based grease
may still be used at other plants and could result in similar failures.

This information notice requires no specific action or written response.  If
you have any questions about the information in this notice, please contact
the technical contact listed below or the appropriate Office of Nuclear
Reactor Regulation (NRR) project manager.


                                      ORIGINAL SIGNED BY 

                                   Brian K. Grimes, Director
                                   Division of Operating Reactor Support
                                   Office of Nuclear Reactor Regulation

Technical contact:  Mark D. Pratt, NRR
                     (301) 504-2701

Attachment: 
List of Recently Issued NRC Information Notices
.