Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
January 31, 1994
NRC INFORMATION NOTICE 93-26, SUPPLEMENT 1: 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 supplement information regarding a problem with a 400-amp frame,
600-V ac 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 (ESF) actuated at the
Nine Mile Point Nuclear Station Unit 2 (NMP2) 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 purge system) 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 close circuit breaker CB-4 manually to
restore the UPS loads. The UPS loads lost power for approximately 12 minutes
during the event.
After Information Notice (IN) 93-26 was issued on April 7, 1993, additional
information was obtained from GE and NMP2. The additional information in
this supplement is intended to assist recipients in determining the
significance of this potential failure mode at their facilities.
9401250302.
IN 93-26, Supp. 1
January 31, 1994
Page 2 of 3
Discussion
Niagara Mohawk Power Corporation, the licensee for Nine Mile Point 2
(LER 92-007-00), and Wyle Laboratories (Report No. 42370-RCCB-1) determined
that circuit breaker CB-4 had failed to close because the grease used at the
pivot points inside the breaker had dried out and solidified. When the grease
dried out, the metal-to-metal contact areas experienced increased friction and
eventual gouging. The 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.
Certain observations were made in the NMP2 analysis relative to these
breakers:
1. The safety function of these breakers is both to open and close
automatically. Normally, the only electrical safety function of a
breaker is its ability to trip. None of the breakers of this type at Nine
Mile Point 2 have failed to trip when required.
2. Due to the nature of the application of these molded-case switches, they
were cycled extensively (approximately 200-400 times). This is more than
a normal molded-case circuit breaker used in a distribution panel.
3. The breakers were in close proximity to the UPS transformers causing
operation above normal ambient conditions, which may or may not have
contributed to the solidification of the grease.
GE has stated that in early 1980 the soap-based and clay-based grease used in
this style molded-case circuit breakers was replaced with a synthetic
lubricant as a product enhancement. However, older molded-case circuit
breakers using the clay-based and soap-based grease may still be in use at
other plants, in similar applications.
.
IN 93-26, Supp. 1
January 31, 1994
Page 3 of 3
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.
/s/'d by BKGrimes
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
