United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 95-22: Hardened Or Contaminated Lubricants Cause Metal-Clad Circuit Breaker Failures

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                            WASHINGTON, D.C.  20555

                                April 21, 1995

                               METAL-CLAD CIRCUIT BREAKER FAILURES


All holders of operating licenses or construction permits for nuclear power


The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to problems that could result from failing to
periodically check the condition of lubricants that may become hardened or
contain contaminants used in HK series (4-kV and 6.9-kV) and K-Line (600-V)
circuit breakers manufactured by Asea Brown Boveri (ABB, formerly ITE) and 
DB-50 (480-V) breakers manufactured by Westinghouse.  It is expected that
recipients will review this 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

Hardened Grease in Breaker Operating Mechanisms

On October 4, 1988, during surveillance testing of the low-pressure core spray
pump at River Bend, Unit 1, the safety-related ABB HK 4-kV circuit breaker
failed to close after the closing circuit was energized from the control room. 
The failure was attributed to breaker linkage grease that had solidified with
age, thus causing the closing mechanism to bind.

On February 8, 1989, during post maintenance testing at D.C. Cook, Unit 1, an
ABB HK 4-kV breaker failed to close after the closing circuit was energized. 
On February 27, 1989, another HK breaker failed to close during a test.  Both
failures were attributed to hardened grease that caused the operating
mechanism to bind.  Seven additional HK series breakers used in safety-related
and balance-of-plant applications also failed in this manner.  The breakers
were 17 years old and had been inspected and serviced several times.  However,
the revision of the vendor manual in use and, consequently, licensee
procedures did not state the need to disassemble, clean or relubricate the
operating mechanism on a periodic basis, except when grease is found to be
"contaminated" or when parts are replaced (see NRC Inspection Report
50-315/89031 for additional information).

9504180073.                                                            IN 95-22
                                                            April 21, 1995
                                                            Page 2 of 4  

During an October 1992 surveillance test at LaSalle, Unit 1, an ABB HK 4-kV
reactor recirculation pump breaker failed to trip.  The failure was attributed
to hardened grease in the operating mechanism.  In October 1993, during a Unit
2 refueling outage, a nonsafety-related ABB HK 4-kV pump breaker failed to
close.  This failure also was attributed to hardened operating mechanism
grease.  The licensee breaker maintenance procedures did not require
inspection (other than visual), disassembly, or relubrication of the breaker
operating mechanism on a periodic basis (see NRC Inspection Report 50-373/
93031 for additional information).

Contamination of Grease on Sliding Electrical Parts

On November 5, 1989, during surveillance testing at D.C. Cook, a Westinghouse
DB-50 480-V "B" train reactor trip bypass breaker failed to close electrically
because of high resistance in the auxiliary contacts that were part of the
closing circuit.  The high resistance may have resulted from contamination of
the conductive graphite grease prescribed by the vendor manual.  The revision
of the Westinghouse instruction manual in use at D.C. Cook did not contain a
recommendation for periodically replacing the graphite grease or checking its
condition (e.g., by measuring contact resistance).  However, recent guidance
issued by the vendor provided for such checking and replacement, as required.


The ABB HK breakers failed because lubricating grease solidified with age in
the breaker operating mechanisms.  As the grease hardened, friction increased
in the metal-to-metal contact areas.  The additional metal friction, as well
as some interference from hardened grease deposits, caused the mechanism to
become increasingly difficult to operate freely, eventually resulting in
failures of the breakers to open or close.  The circuit breakers discussed
above had been routinely inspected on numerous occasions.  However, while the
licensees adequately verified cleanliness in the visual inspections, they
failed to identify lubricant that was solidified or contaminated.  Preventive
maintenance activities did not include periodic cleaning or disassembly of the
operating mechanism to determine if the operating mechanism should be

Until 1991, all the revisions to the ITE/ABB HK and K-Line vendor manuals
stated that breaker operating mechanisms were factory lubricated and should
not require additional lubrication during breaker service life.  However, as
early as 1972, ABB manuals, such as ITE HK Switchgear Instruction Book
IB-8.2.7-1, and medium-voltage switchgear maintenance and surveillance manuals
MS (for HK) and MS (for K-Line), did call for cleaning
and relubrication of the mechanism with ANDEROL 757 grease (or NO-OX-ID grease
for mating surfaces of moving, current-carrying joints) should any lubricant
be found contaminated or when parts are replaced.

In response to a 1989 10 CFR Part 21 report from D.C. Cook of mechanism
binding due to hardened grease, ABB sent a letter to the NRC and all known
affected licensees or purchasers of HK and K-Line breakers that described the

                                                            IN 95-22     
                                                            April 21, 1995
                                                            Page 3 of 4  

problem and recommended solutions.  LaSalle, for example, had received this
letter, yet had not updated procedures to prevent the 1992 and 1993 failures. 
Other plants with the affected breakers included Perry, Comanche Peak, and
Fermi.  Comanche Peak had taken action to prevent these failures.

In 1991, ABB issued revisions to the HK and K-Line manuals that called for
periodic (10-year) cleaning and relubrication of the operating mechanism with
ANDEROL 757 and the mating surfaces of moving, current-carrying joints with
the NO-OX-ID, although mechanical failures to operate have only been
attributed to hardened mechanism lubricant.  In September 29 and October 3,
1994, letters to the NRC, ABB stated, on the basis of recent refurbishments,
that the condition of the mechanism lubricant cannot be determined without
complete disassembly of the mechanism.  The October letter also cited failures
of K3000 breakers as a result of hardened mechanism lubricant, but stated that
although failures of smaller K-Line breakers attributable to hardened
mechanism grease had not been reported, some had operated sluggishly.  Repor-
tedly, most of these breakers also have not been periodically disassembled,
cleaned, or relubricated in service.  In performing post maintenance testing,
licensees found no evidence of impending breaker failures due to hardened
grease because the tests were performed primarily to determine whether the
breaker tripped or closed.

Unusual service conditions such as high ambient temperatures, very dirty
atmosphere during construction or outages or mixing of incompatible greases
were not specifically identified in the instances cited.  However, such
conditions accelerate hardening of mechanism lubricants and are conducive to
dirt or chemical contamination and increased electrical resistance of
electrical part lubricants.  Note that ESSO/Humble (now EXXON) NEBULA EP5F
grease was used for these breakers prior to March 1972.  After this date, new
breaker mechanisms were factory-lubricated with ANDEROL 757.  Manufacturers
have warned that old (or unidentified) grease should be completely removed
before relubricating.

Although referring to a different type of circuit breaker, NRC IN 93-26,
"Grease Solidification Causes Molded-Case Circuit Breaker Failure to Close,"
issued April 7, 1993, and its supplement issued January 31, 1994, described a
similar problem.  In addition, addressees are reminded of commitments made in
response to the staff position in Generic Letter 90-03 and its Supplement 1,
to maintain contact with certain key vendors (which include Class 1E
switchgear vendors), in order to ensure that manuals (and equipment) are kept
up to date and the latest technical information (including 10 CFR Part 21
reports and related correspondence) is promptly obtained, evaluated for
applicability, and acted on, as appropriate.  Recommendations for switchgear
maintenance can also be found in owners group documents (e.g., the
Westinghouse Owners Group guidelines on DB and DS breaker maintenance) and
industry guidance such as National Electrical Manufacturers Association (NEMA)
publications, American National Standards Institute/Institute of Electrical
and Electronic Engineers (ANSI/IEEE) standards, and various Electric Power
Research Institute (EPRI) reports such as NP-7410, "Breaker Maintenance."

                                                            IN 95-22     
                                                            April 21, 1995
                                                            Page 4 of 4  

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

                                    /s/'d by CIGrimes/for

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

Technical contacts:  Rogelio Mendez, RIII
                     (708) 829-9745

                     Stephen D. Alexander, NRR
                     (301) 415-2995

                     Sikhindra K. Mitra, NRR
                     (301) 415-2783

                     Tirupataiah Tella, RIII
                     (708) 829-9749

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