Information Notice 2007-34, Operating Experience Regarding Electrical Circuit Breakers

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Operating Experience Regarding Electrical Circuit Breakers
ML072390061
Person / Time
Issue date: 10/22/2007
From: Michael Case
NRC/NRR/ADRA/DPR
To:
Joseph Giantelli, NRR/DIRS/IOEB
References
IN-07-034
Download: ML072390061 (6)
v • d • e


UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, DC 20555-0001 October 22, 2007 NRC INFORMATION NOTICE 2007-34: OPERATING EXPERIENCE REGARDING

ELECTRICAL CIRCUIT BREAKERS

ADDRESSEES

All holders of operating licenses for nuclear power reactors, except those who have

permanently ceased operations and have certified that fuel has been permanently removed

from the reactor vessel.

PURPOSE

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform

addressees about operating experience regarding low-, medium-, and high-voltage circuit

breakers. The NRC expects that recipients will review the information for applicability to their

facilities and consider appropriate actions to avoid similar problems. Suggestions contained in

this IN are not NRC requirements; therefore, no specific action or written response is required.

DESCRIPTION OF CIRCUMSTANCES

The Office of Nuclear Reactor Regulation (NRR) reviewed recent operating experience related

to electrical circuit breakers and found that breaker problems were often caused by the

following:

  • Deficient fit-up with cubicles
  • Inadequate or excessive tolerances and gaps
  • Worn or misadjusted operating linkages
  • Inadequate or inappropriate maintenance practices
  • Configuration control errors
  • Deficiencies from original design and refurbishment
  • Design changes

The following are examples of recent circuit breaker problems:

River Bend Station Unit 1

On May 27, 2006, while the unit was operating at 100 percent power, the licensee determined

that one of the required offsite power supplies to the Division 3 standby switchgear had been

inoperable because a 4160-volt circuit breaker was not functional. The licensee found that the

breaker was not fully racked in and the racking mechanism was unusually difficult to operate.

The licensee had an outstanding maintenance work order to address that the control power light

for the breaker in the main control room was not illuminated, which it turned out was due to the

breaker not being fully racked in. The licensee also found that one of the permissive signals

necessary to close the breaker was not present - the next breaker upstream was not closed.

The licensee found that the surveillance test procedures for verifying the alignment of offsite

power supplies did not verify the supplies to Division 3. Corrective actions included (1) revising

the operations procedure for breaker racking to verify indication of control power, and to perform

a functional test of breakers that support a safety function; and (2) revising the technical

specification bases and surveillance test procedure to verify the alignment of breakers to the

Division 3 switchgear. (LER 50-458/2006-006, ADAMS Accession No. ML062130074)

Crystal River Unit 3

In November 2006, the licensee found that the 1A emergency diesel generator was inoperable

because the breaker charging motor direct current power control switch was found in the off

position and the breaker closing spring was not charged. Since the breaker performed as

expected during post-maintenance testing, operations and maintenance personnel did not

recheck or verify the position of the toggle switch, which is located in the closed breaker cubicle.

The problem was subsequently revealed during the next periodic surveillance test.

(LER 50-302/2006-002, ADAMS Accession No. ML070030513)

Indian Point Unit 2

On January 2, 2007, during quarterly surveillance testing, a residual heat removal pump failed

to start on demand. A control power fuse had blown in the pump 480-volt alternating current

electrical supply breaker, a Westinghouse type DB-50 breaker. The licensee found that the

inertia latch (which is designed to prevent a breaker re-closure due to contact bounce following

a breaker trip) was binding and did not reset following the last breaker trip operation causing the

closing coil to remain energized until the protective fuses opened. Foreign material was found

imbedded on the surface of the inertia latch bushing creating a rough and uneven surface. As

corrective actions, the licensee cleaned and lubricated the inertia latch and changed the breaker

preventive maintenance procedure to emphasize the importance of assuring freedom of

movement and smooth operation of the inertia latch. (LER 50-247/2007-001, ADAMS

Accession No. ML070650407)

Fort Calhoun

On January 25, 2007, the 4160-volt circuit breaker for the train B raw water pump closed on

demand which started the pump but the mechanical-operated contact (MOC) switch did not

actuate the auxiliary contacts that provide breaker position indication and provide a signal to

open the discharge valve from the pump when the circuit breaker is closed. The MOC switch

failure was the result of a broken MOC offset rod, a metal rod that transfers the motion of the

circuit breaker to operate the auxiliary contacts. One month earlier, the C raw pump had also

been rendered inoperable due to a broken MOC offset rod. In 1995, all of the stations

4160-volt General Electric (GE) Magna-Blast circuit breakers were replaced with breakers from

Asea Brown Boveri Services Company that were designed to fit in the GE switchgear. The

licensees root cause analysis determined that design processes failed to recognize and properly evaluate the additional stresses placed on MOC offset rod by a metal test flag device, an accessory used during circuit breaker testing. As corrective actions, the licensee replaced

the MOC offset rod in the A and D raw water pumps circuit breakers and other 4160-volt

safety-related circuit breakers having more than 1000 cycles of operation were rebuilt with rods

having fewer than 1000 cycles of operation. (LER 50-285/2007-002, ADAMS Accession No.

ML071070290)

Farley Unit 1

While performing an EDG operability test on April 26, 2007, the licensee determined that the

MOC switch of the 1C EDG output breaker was not being fully activated when the breaker was

closed. Operators declared the EDG inoperable. The licensee determined that the MOC

switch, which is used to provide auxiliary contacts for breaker status indication and other control

functions, was not rotating sufficiently to fully engage the normally open contacts. The event

was the result of a fit-up discrepancy during replacement of the existing Allis Chalmers breakers

with new Cutler Hammer breakers within the Allis Chalmers switchgear. The fit-up discrepancy

went unrecognized because of inadequate procedural guidance on how the replacement

breakers were to be set up during initial installation and testing. (LER 50-348/2007-001, ADAMS Accession No. ML071760334)

Other Circuit Breaker Issues

The NRC review of operating experience also revealed the following circuit breaker issues

involving inadequate maintenance practices:

  • Inadequate maintenance practices have resulted in gaps/clearances in the breaker

mechanism becoming out of specification and preventing proper operation of the circuit

breaker.

  • Inadequate maintenance practices have resulted in not properly clearing and resetting

the trip mechanism once the circuit breaker is fully racked in the connect position. This

would prevent the circuit breaker to close on demand.

  • Inadequate maintenance practices have resulted in main stabs with excessive wear

leading to misalignment while racking the circuit breaker into the cubicle. This has led to

the failure of the high-resistance stab connection, which caused an electrical fault.

  • Inadequate maintenance practices have resulted in misalignment of the circuit breaker to

the cubicle for circuit breaker racking operation. Misalignment has led to control power

contacts not connecting when the circuit breaker is racked in. Also, instances of

inadequate assessment, cleaning, and testing of contacts (relay, switch, contacts, etc.)

have led to the circuit breaker not operating in accordance with its design.

  • Inadequate maintenance practices have involved crimping of control power lead lugs.

Faulty crimps have caused control power losses. There are also instances of loose

connections not being identified and/or corrected. * Inadequate maintenance practices have involved cleaning (including hardened greases)

and greasing of the circuit breaker mechanism. This can result in the circuit breaker

mechanism and auxiliary switch not operating in accordance with their design.

  • Inadequate maintenance practices have caused inadvertent actuation of relays mounted

on circuit breaker cubicle doors during circuit breaker maintenance.

BACKGROUND

Previous Related Generic Communications:

  • IN 1999-13, Insights from NRC Inspections of Low- and Medium-Voltage Circuit

Breaker Maintenance Programs (ADAMS Accession No. ML031040447)

Maintenance (ADAMS Accession No. ML051740051)

  • IN 2005-15, Three-Unit Trip and Loss of Offsite Power at Palo Verde Nuclear

Generating Station (ADAMS Accession No. ML050490364)

  • IN 2006-18, Supplement 1, Significant Loss of Safety-Related Electrical Power at

Forsmark Unit 1 in Sweden (ADAMS Accession No. ML071900368)

  • IN 2006-31, Inadequate Fault Interrupting Rating of Breakers (ADAMS Accession

No. ML063000104)

  • IN 2007-14, Loss of Offsite Power and Dual-Unit Trip at Catawba Nuclear Generating

Station (ADAMS Accession No. ML070610424)

DISCUSSION

Licensees rely on electrical circuit breakers being operable to satisfy many technical

specification (TS) requirements which includes TSs related to electrical power, as well as, many

other TSs because for a system to be considered operable, it must have all necessary attendant

instrumentation, controls, normal or emergency electrical power. Circuit breakers are relied

upon to provide electrical power to equipment credited in accident analysis. Because licensees

often use the breakers of the same type and manufacturers in redundant trains of several safety

systems, certain breaker problems raise the possibility of a common mode failure. In particular, several licensees have experienced problems following a modification that installs replacement

breakers of a different manufacturer into the existing switchgear.

CONTACT

This IN requires no specific action or written response. Please direct any questions about this

matter to the technical contact listed below.

/RA by TQuay for/

Michael J. Case, Director

Division of Policy and Rulemaking

Office of Nuclear Reactor Regulation

Technical Contacts: Joseph Giantelli, DIRS/IOEB Kenn Miller, DE/EEEB

301-415-0504 301-415-3152 E-mail: jmg8@nrc.gov E-mail: kam4@nrc.gov

Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.

CONTACT

This IN requires no specific action or written response. Please direct any questions about this

matter to the technical contact listed below.

/RA by TQuay for/

Michael J. Case, Director

Division of Policy and Rulemaking

Office of Nuclear Reactor Regulation

Technical Contacts: Joseph Giantelli, DIRS/IOEB Kenn Miller, DE/EEEB

301-415-0504 301-415-3152 E-mail: jmg8@nrc.gov E-mail: kam4@nrc.gov

Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.

Distribution:

IN File

  • Concurred via email

ADAMS Accession Number: ML072390061 OFFICE DIRS:IOEB EEEB Tech Editor* BC:EEEB D:DE

NAME JGiantelli KMiller HChang GWilson PHiland

DATE 9/28/2007 10/9/2007 8/29/2007 10/10/07 10/15/2007 OFFICE DPR:PGCB DPR:PGCB BC:DPR:PGCB D:NRR:DPR

NAME DBeaulieu CHawes MMurphy TQuay for MCase

DATE 10/17/2007 10/17/2007 10/18/2007 10/22/2007 OFFICIAL RECORD COPY


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