Information Notice 2008-21, Impact of Non-Safety Electrical Support System Vulnerabilities on Safety Systems: Difference between revisions

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| issue date = 11/24/2008
| issue date = 11/24/2008
| title = Impact of Non-Safety Electrical Support System Vulnerabilities on Safety Systems
| title = Impact of Non-Safety Electrical Support System Vulnerabilities on Safety Systems
| author name = Dorman D H, Shea J W
| author name = Dorman D, Shea J
| author affiliation = NRC/NMSS/FCSS, NRC/RGN-II/DFFI
| author affiliation = NRC/NMSS/FCSS, NRC/RGN-II/DFFI
| addressee name =  
| addressee name =  
Line 13: Line 13:
| document type = NRC Information Notice
| document type = NRC Information Notice
| page count = 4
| page count = 4
| revision = 0
}}
}}
{{#Wiki_filter:ML082730593 November 24, 2008 NRC INFORMATION NOTICE 2008-21: IMPACT OF NON-SAFETY ELECTRICAL SUPPORT SYSTEM VULNERABILITIES ON SAFETY SYSTEMS ADDRESSES All holders of operating licenses for nuclear fuel facilitie
{{#Wiki_filter:UNITED STATES
 
NUCLEAR REGULATORY COMMISSION
 
OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS
 
WASHINGTON, D.C. 20555 November 24, 2008 NRC INFORMATION NOTICE 2008-21:                 IMPACT OF NON-SAFETY ELECTRICAL
 
SUPPORT SYSTEM VULNERABILITIES ON
 
SAFETY SYSTEMS
 
ADDRESSES
 
All holders of operating licenses for nuclear fuel facilities.


==PURPOSE==
==PURPOSE==
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform addressees about potential impacts of non-safety support system failures or vulnerabilities on safety system This IN references operating experience regarding low-, medium-, and high-voltage circuit breakers as described in IN 2007-34 and adds similar operating experience of non-safety related breakers at fuel facilitie Information Notice 2007-34 is attache Licensees rely on non-safety electrical systems to satisfy many items relied on for safety (IROFS), technical safety requirements (TSR), or plant features (PF). For IROFS/TSRs/PFs to be considered available and reliable, they must have necessary instrumentation, controls, and normal or emergency electrical power availabl It is expected that recipients will review the information for applicability to their facilities and consider appropriate actions to avoid similar problem Suggestions contained in this IN are not NRC requirements; therefore, no specific action or written response is require DESCRIPTION OF CIRCUMSTANCES The Region II Division of Fuel Facility Inspection reviewed operating experience for the past five years at both power reactors and fuel facilities related to electrical circuit breakers and found that breaker problems were often caused by the following:
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform
Deficient fit-up with cubicles Worn or misadjusted linkages Inadequate or inappropriate maintenance practices Configuration control errors Deficiencies from original design and refurbishment Design changes Foreign material entry UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS WASHINGTON, D.C. 20555 The following are examples of circuit breaker problems at fuel facilities:
 
BWX Technologies On November 17, 2007, heavy smoke was emanating from the vicinity of an electrical transforme The fire, which emanated from a shorted 480 volt fuse panel, had melted nearby plastic material and caused nearby wooden material to ignite and smolde Immediate event review by the licensee determined that an electrical surge was halted when the 12.4 kilovolt gang-operated switch disconnected the power supply transformer from the utility sub-statio The licensee's root causes for the fire were human performance such that the preventative maintenance on the failed breakers was not performed due to production schedules and equipment failur (Inspection Report No. 70-27/2007008, ADAMS Accession No. ML0802503450) The licensee stated in their root cause analysis that the fire was the result of an electrical faul The branch circuit and the main breaker feeding the transformer failed to open as designed allowing a sustained fault condition resulting in the fir Paducah Gaseous Diffusion Plant On May 20, 2003, the plant staff identified a fire in a non-safety related 480 volt circuit breaker located in the Building C-633 Pump Hous The circuit breaker provided power to a motor associated with a recirculating water cooling tower fa Due to problems within the circuit breaker, the breaker did not immediately de-energize after the fault occurre Instead, after approximately 8 seconds, the breaker was de-energized after the setpoints associated with a back-up current limiting device were exceede As a result of the delayed de-energizing of the electrical breaker, other nearby breakers were damaged during the resultant fir No personnel injuries occurred as a result of the fire and no safety-related equipment was affected. (Inspection Report No. 70-7001/2003005, ADAMS Accession No. ML032020568)
addressees about potential impacts of non-safety support system failures or vulnerabilities on
Paducah Gaseous Diffusion Plant On November 23, 2004, the 480 volt Transformer Service Breaker 2PPA1 was being returned to service when a fault occurred resulting in a fir Non-safety plant equipment that should have operated to isolate the fault failed to function and, as a result, the fault remained energized for approximately 11 minute After the fault was isolated, the plant fire brigade used water to extinguish the fir No release of radioactive material occurred and no plant personnel were injured; however, a significant plant transient resulte The certificate holder's root cause analysis determined that foreign material had caused the fault, and that the failure of other breakers to properly operate caused additional damage to the switchgea Short term and long term corrective actions were initiated (Inspection Report No. 70-7001/2005001, ADAMS Accession No. ML050620142) 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 breake
safety systems. This IN references operating experience regarding low-, medium-, and
* Inadequate maintenance practices have resulted in not properly clearing and resetting the trip mechanism once the circuit breaker is fully racked into the connect position - preventing the circuit breaker from closing on deman
 
* Inadequate maintenance practices have resulted in main stabs with excessive wear leading to misalignment while racking the circuit breaker into the cubicl This has led to the failure of the high-resistance stab connection, which caused an electrical faul
high-voltage circuit breakers as described in IN 2007-34 and adds similar operating experience
* Inadequate maintenance practices have resulted in misalignment of the circuit breaker within the panel or cubicl Misalignment has led to control power contacts not connecting when the circuit breaker is racked i 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 desig
 
* Inadequate maintenance practices have involved crimping of control power lead lugs. Faulty crimps have caused control power losse There are also instances of loose connections not being identified and/or correcte
of non-safety related breakers at fuel facilities. Information Notice 2007-34 is attached.
* Inadequate maintenance practices have involved inadequate cleaning (including hardened greases) and greasing of the circuit breaker mechanis This can result in the circuit breaker mechanism and auxiliary switch not operating in accordance with their desig
 
* Inadequate maintenance practices have caused inadvertent actuation of relays mounted on circuit breaker cubicle doors during circuit breaker maintenanc
Licensees rely on non-safety electrical systems to satisfy many items relied on for safety
 
(IROFS), technical safety requirements (TSR), or plant features (PF). For IROFS/TSRs/PFs to
 
be considered available and reliable, they must have necessary instrumentation, controls, and
 
normal or emergency electrical power available.
 
It is expected 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 Region II Division of Fuel Facility Inspection reviewed operating experience for the past five
 
years at both power reactors and fuel facilities related to electrical circuit breakers and found
 
that breaker problems were often caused by the following:
Deficient fit-up with cubicles
 
===Worn or misadjusted linkages===
Inadequate or inappropriate maintenance practices
 
===Configuration control errors===
Deficiencies from original design and refurbishment
 
===Design changes===
Foreign material entry
 
The following are examples of circuit breaker problems at fuel facilities:
 
===BWX Technologies===
On November 17, 2007, heavy smoke was emanating from the vicinity of an electrical
 
transformer. The fire, which emanated from a shorted 480 volt fuse panel, had melted nearby
 
plastic material and caused nearby wooden material to ignite and smolder.
 
Immediate event review by the licensee determined that an electrical surge was halted when the
 
12.4 kilovolt gang-operated switch disconnected the power supply transformer from the utility
 
sub-station. The licensees root causes for the fire were human performance such that the
 
preventative maintenance on the failed breakers was not performed due to production
 
schedules and equipment failure. (Inspection Report No. 70-27/2007008, ADAMS Accession
 
No. ML0802503450) The licensee stated in their root cause analysis that the fire was the result
 
of an electrical fault. The branch circuit and the main breaker feeding the transformer failed to
 
open as designed allowing a sustained fault condition resulting in the fire.
 
===Paducah Gaseous Diffusion Plant===
On May 20, 2003, the plant staff identified a fire in a non-safety related 480 volt circuit breaker
 
located in the Building C-633 Pump House. The circuit breaker provided power to a motor
 
associated with a recirculating water cooling tower fan. Due to problems within the circuit
 
breaker, the breaker did not immediately de-energize after the fault occurred. Instead, after
 
approximately 8 seconds, the breaker was de-energized after the setpoints associated with a
 
back-up current limiting device were exceeded. As a result of the delayed de-energizing of the
 
electrical breaker, other nearby breakers were damaged during the resultant fire. No personnel
 
injuries occurred as a result of the fire and no safety-related equipment was affected.
 
(Inspection Report No. 70-7001/2003005, ADAMS Accession No. ML032020568)
 
===Paducah Gaseous Diffusion Plant===
On November 23, 2004, the 480 volt Transformer Service Breaker 2PPA1 was being returned to
 
service when a fault occurred resulting in a fire. Non-safety plant equipment that should have
 
operated to isolate the fault failed to function and, as a result, the fault remained energized for
 
approximately 11 minutes. After the fault was isolated, the plant fire brigade used water to
 
extinguish the fire. No release of radioactive material occurred and no plant personnel were
 
injured; however, a significant plant transient resulted. The certificate holders root cause
 
analysis determined that foreign material had caused the fault, and that the failure of other
 
breakers to properly operate caused additional damage to the switchgear. Short term and long
 
term corrective actions were initiated (Inspection Report No. 70-7001/2005001, ADAMS
 
Accession No. ML050620142) 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 into the connect position -
        preventing the circuit breaker from closing 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
 
within the panel or cubicle. 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 inadequate 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==
==BACKGROUND==
Previous Related Generic Communications:
Previous Related Generic Communications:
* IN 1999-13, "Insights from NRC Inspections of Low- and Medium-Voltage Circuit Breaker Maintenance Programs" (ADAMS Accession No. ML031040447)
*   IN 1999-13, Insights from NRC Inspections of Low- and Medium-Voltage Circuit Breaker
* IN 2005-21, "Plant Trip and Loss of Preferred AC Power From Inadequate Switchyard 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)
Maintenance Programs (ADAMS Accession No. ML031040447)
* IN 2006-18, Supplement 1, "Significant Loss of Safety-Related Electrical Power at Forsmark Unit 1 in Sweden" (ADAMS Accession No. ML071900368)
*   IN 2005-21, Plant Trip and Loss of Preferred AC Power From Inadequate Switchyard
* 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 non-safety electrical circuit breakers to power many IROFS, TSRs, or PFs related to electrical powe For IROFS/TSRs/PFs to be considered available and reliable, they must have all necessary instrumentation, controls, and normal or emergency electrical power availabl Circuit breakers are relied upon to provide electrical power to equipment credited in the integrated safety analysis or safety analysis repor Licensees should incorporate the industry experience highlighted in this, and the above information notices, in electrical circuit breaker maintenance program Maintenance programs should identify and emphasize the importance of electrical systems which support important safety system Because licensees often use breakers of the same type and manufacture in various electrical support systems throughout the plant, common mode failure possibilities should be evaluated when performing modifications or other maintenanc When failures do occur, the extent of condition should be thoroughly evaluated for the potential for poor maintenance practices or design issues to impact other important site electrical system
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 non-safety electrical circuit breakers to power many IROFS, TSRs, or PFs
 
related to electrical power. For IROFS/TSRs/PFs to be considered available and reliable, they
 
must have all necessary instrumentation, controls, and normal or emergency electrical power
 
available. Circuit breakers are relied upon to provide electrical power to equipment credited in
 
the integrated safety analysis or safety analysis report. Licensees should incorporate the
 
industry experience highlighted in this, and the above information notices, in electrical circuit
 
breaker maintenance programs. Maintenance programs should identify and emphasize the
 
importance of electrical systems which support important safety systems. Because licensees
 
often use breakers of the same type and manufacture in various electrical support systems
 
throughout the plant, common mode failure possibilities should be evaluated when performing
 
modifications or other maintenance. When failures do occur, the extent of condition should be
 
thoroughly evaluated for the potential for poor maintenance practices or design issues to impact
 
other important site electrical systems.


==CONTACT==
==CONTACT==
This IN requires no specific action or written respons Please direct any questions about this matter to the technical contact listed belo /RA/ /RA/ Joseph W. Shea, Director Division of Fuel Facility Inspection Region II Daniel H. Dorman, Director Division of Fuel Cycle Safety and Safeguards Office of Nuclear Material Safety and Safeguards  
This IN requires no specific action or written response. Please direct any questions about this
 
matter to the technical contact listed below.
 
/RA/                                                         /RA/
Joseph W. Shea, Director                             Daniel H. Dorman, Director
 
Division of Fuel Facility Inspection                  Division of Fuel Cycle Safety and
 
Region II                                            Safeguards
 
Office of Nuclear Material Safety and
 
Safeguards


===Technical Contact:===
===Technical Contact:===
Mary L. Thomas, DFFI/ FFIB3 404.562.4561 E-mail: MaryLynne.Thomas@nrc.gov  
Mary L. Thomas, DFFI/ FFIB3
                        404.562.4561 E-mail: MaryLynne.Thomas@nrc.gov
 
Enclosure:      IN 2007-34, Operating Experience Regarding Electrical Circuit Breakers *    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)


===Enclosure:===
==DISCUSSION==
IN 2007-34, Operating Experience Regarding Electrical Circuit Breakers
Licensees rely on non-safety electrical circuit breakers to power many IROFS, TSRs, or PFs related to electrical
* 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)
power. For IROFS/TSRs/PFs to be considered available and reliable, they must have all necessary instrumentation, controls, and normal or emergency electrical power available. Circuit breakers are relied upon to provide electrical
* 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 non-safety electrical circuit breakers to power many IROFS, TSRs, or PFs related to electrical powe For IROFS/TSRs/PFs to be considered available and reliable, they must have all necessary instrumentation, controls, and normal or emergency electrical power availabl Circuit breakers are relied upon to provide electrical power to equipment credited in the integrated safety analysis or safety analysis repor Licensees should incorporate the industry experience highlighted in this, and the above information notices, in electrical circuit breaker maintenance program Maintenance programs should identify and emphasize the importance of electrical systems which support important safety system Because licensees often use breakers of the same type and manufacture in various electrical support systems throughout the plant, common mode failure possibilities should be evaluated when performing modifications or other maintenanc When failures do occur, the extent of condition should be thoroughly evaluated for the potential for poor maintenance practices or design issues to impact other important site electrical system
power to equipment credited in the integrated safety analysis or safety analysis report. Licensees should incorporate
 
the industry experience highlighted in this, and the above information notices, in electrical circuit breaker
 
maintenance programs. Maintenance programs should identify and emphasize the importance of electrical systems
 
which support important safety systems. Because licensees often use breakers of the same type and manufacture in
 
various electrical support systems throughout the plant, common mode failure possibilities should be evaluated when
 
performing modifications or other maintenance. When failures do occur, the extent of condition should be thoroughly
 
evaluated for the potential for poor maintenance practices or design issues to impact other important site electrical
 
systems.


==CONTACT==
==CONTACT==
This IN requires no specific action or written respons Please direct any questions about this matter to the technical contact listed belo Joseph W. Shea, Director Division of Fuel Facility Inspection Region II Daniel H. Dorman, Director Division of Fuel Cycle Safety and Safeguards Office of Nuclear Material Safety and Safeguards  
This IN requires no specific action or written response. Please direct any questions about this matter to the technical
 
contact listed below.
 
Joseph W. Shea, Director                                         Daniel H. Dorman, Director
 
Division of Fuel Facility Inspection                              Division of Fuel Cycle Safety and Safeguards
 
Region II                                                        Office of Nuclear Material Safety and Safeguards


===Technical Contact:===
===Technical Contact:===
Mary L. Thomas, DFFI/ FFIB3 404.562.4561 E-mail: MaryLynne.Thomas@nrc.gov  
Mary L. Thomas, DFFI/ FFIB3
                            404.562.4561 E-mail: MaryLynne.Thomas@nrc.gov
 
Enclosure:          IN 2007-34, Operating Experience Regarding Electrical Circuit Breakers
 
DISTRIBUTION:
*see previous concurence
 
ML082730593 OFFICE        DFFI/FFIB3            DFFI/FFIB3 RII/FFI                        NMSS/FCSS


===Enclosure:===
NAME          M. Thomas*            D. Rich*        J. Shea*                  D. Dorman
IN 2007-34, Operating Experience Regarding Electrical Circuit Breakers


DISTRIBUTION: *see previous concurence ML082730593 OFFICE DFFI/FFIB3 DFFI/FFIB3RII/FFI NMSS/FCSS NAME M. Thomas* D. Rich* J. Shea* D. Dorman DATE 10/1/08 10/1/08 MCL 10/30/08 10/31/08}}
DATE           10/1/08               10/1/08         MCL 10/30/08             10/31/08 OFFICIAL USE ONLY}}


{{Information notice-Nav}}
{{Information notice-Nav}}

Latest revision as of 13:30, 14 November 2019

Impact of Non-Safety Electrical Support System Vulnerabilities on Safety Systems
ML082730593
Person / Time
Issue date: 11/24/2008
From: Dan Dorman, James Shea
NRC/NMSS/FCSS, NRC/RGN-II/DFFI
To:
References
IN-08-021
Download: ML082730593 (4)
v • d • e


UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS

WASHINGTON, D.C. 20555 November 24, 2008 NRC INFORMATION NOTICE 2008-21: IMPACT OF NON-SAFETY ELECTRICAL

SUPPORT SYSTEM VULNERABILITIES ON

SAFETY SYSTEMS

ADDRESSES

All holders of operating licenses for nuclear fuel facilities.

PURPOSE

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

addressees about potential impacts of non-safety support system failures or vulnerabilities on

safety systems. This IN references operating experience regarding low-, medium-, and

high-voltage circuit breakers as described in IN 2007-34 and adds similar operating experience

of non-safety related breakers at fuel facilities. Information Notice 2007-34 is attached.

Licensees rely on non-safety electrical systems to satisfy many items relied on for safety

(IROFS), technical safety requirements (TSR), or plant features (PF). For IROFS/TSRs/PFs to

be considered available and reliable, they must have necessary instrumentation, controls, and

normal or emergency electrical power available.

It is expected 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 Region II Division of Fuel Facility Inspection reviewed operating experience for the past five

years at both power reactors and fuel facilities related to electrical circuit breakers and found

that breaker problems were often caused by the following:

Deficient fit-up with cubicles

Worn or misadjusted linkages

Inadequate or inappropriate maintenance practices

Configuration control errors

Deficiencies from original design and refurbishment

Design changes

Foreign material entry

The following are examples of circuit breaker problems at fuel facilities:

BWX Technologies

On November 17, 2007, heavy smoke was emanating from the vicinity of an electrical

transformer. The fire, which emanated from a shorted 480 volt fuse panel, had melted nearby

plastic material and caused nearby wooden material to ignite and smolder.

Immediate event review by the licensee determined that an electrical surge was halted when the

12.4 kilovolt gang-operated switch disconnected the power supply transformer from the utility

sub-station. The licensees root causes for the fire were human performance such that the

preventative maintenance on the failed breakers was not performed due to production

schedules and equipment failure. (Inspection Report No. 70-27/2007008, ADAMS Accession

No. ML0802503450) The licensee stated in their root cause analysis that the fire was the result

of an electrical fault. The branch circuit and the main breaker feeding the transformer failed to

open as designed allowing a sustained fault condition resulting in the fire.

Paducah Gaseous Diffusion Plant

On May 20, 2003, the plant staff identified a fire in a non-safety related 480 volt circuit breaker

located in the Building C-633 Pump House. The circuit breaker provided power to a motor

associated with a recirculating water cooling tower fan. Due to problems within the circuit

breaker, the breaker did not immediately de-energize after the fault occurred. Instead, after

approximately 8 seconds, the breaker was de-energized after the setpoints associated with a

back-up current limiting device were exceeded. As a result of the delayed de-energizing of the

electrical breaker, other nearby breakers were damaged during the resultant fire. No personnel

injuries occurred as a result of the fire and no safety-related equipment was affected.

(Inspection Report No. 70-7001/2003005, ADAMS Accession No. ML032020568)

Paducah Gaseous Diffusion Plant

On November 23, 2004, the 480 volt Transformer Service Breaker 2PPA1 was being returned to

service when a fault occurred resulting in a fire. Non-safety plant equipment that should have

operated to isolate the fault failed to function and, as a result, the fault remained energized for

approximately 11 minutes. After the fault was isolated, the plant fire brigade used water to

extinguish the fire. No release of radioactive material occurred and no plant personnel were

injured; however, a significant plant transient resulted. The certificate holders root cause

analysis determined that foreign material had caused the fault, and that the failure of other

breakers to properly operate caused additional damage to the switchgear. Short term and long

term corrective actions were initiated (Inspection Report No. 70-7001/2005001, ADAMS

Accession No. ML050620142) 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 into the connect position -

preventing the circuit breaker from closing 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

within the panel or cubicle. 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 inadequate 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 non-safety electrical circuit breakers to power many IROFS, TSRs, or PFs

related to electrical power. For IROFS/TSRs/PFs to be considered available and reliable, they

must have all necessary instrumentation, controls, and normal or emergency electrical power

available. Circuit breakers are relied upon to provide electrical power to equipment credited in

the integrated safety analysis or safety analysis report. Licensees should incorporate the

industry experience highlighted in this, and the above information notices, in electrical circuit

breaker maintenance programs. Maintenance programs should identify and emphasize the

importance of electrical systems which support important safety systems. Because licensees

often use breakers of the same type and manufacture in various electrical support systems

throughout the plant, common mode failure possibilities should be evaluated when performing

modifications or other maintenance. When failures do occur, the extent of condition should be

thoroughly evaluated for the potential for poor maintenance practices or design issues to impact

other important site electrical systems.

CONTACT

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

matter to the technical contact listed below.

/RA/ /RA/

Joseph W. Shea, Director Daniel H. Dorman, Director

Division of Fuel Facility Inspection Division of Fuel Cycle Safety and

Region II Safeguards

Office of Nuclear Material Safety and

Safeguards

Technical Contact:

Mary L. Thomas, DFFI/ FFIB3

404.562.4561 E-mail: MaryLynne.Thomas@nrc.gov

Enclosure: IN 2007-34, Operating Experience Regarding Electrical Circuit Breakers * 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 non-safety electrical circuit breakers to power many IROFS, TSRs, or PFs related to electrical

power. For IROFS/TSRs/PFs to be considered available and reliable, they must have all necessary instrumentation, controls, and normal or emergency electrical power available. Circuit breakers are relied upon to provide electrical

power to equipment credited in the integrated safety analysis or safety analysis report. Licensees should incorporate

the industry experience highlighted in this, and the above information notices, in electrical circuit breaker

maintenance programs. Maintenance programs should identify and emphasize the importance of electrical systems

which support important safety systems. Because licensees often use breakers of the same type and manufacture in

various electrical support systems throughout the plant, common mode failure possibilities should be evaluated when

performing modifications or other maintenance. When failures do occur, the extent of condition should be thoroughly

evaluated for the potential for poor maintenance practices or design issues to impact other important site electrical

systems.

CONTACT

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

contact listed below.

Joseph W. Shea, Director Daniel H. Dorman, Director

Division of Fuel Facility Inspection Division of Fuel Cycle Safety and Safeguards

Region II Office of Nuclear Material Safety and Safeguards

Technical Contact:

Mary L. Thomas, DFFI/ FFIB3

404.562.4561 E-mail: MaryLynne.Thomas@nrc.gov

Enclosure: IN 2007-34, Operating Experience Regarding Electrical Circuit Breakers

DISTRIBUTION:

  • see previous concurence

ML082730593 OFFICE DFFI/FFIB3 DFFI/FFIB3 RII/FFI NMSS/FCSS

NAME M. Thomas* D. Rich* J. Shea* D. Dorman

DATE 10/1/08 10/1/08 MCL 10/30/08 10/31/08 OFFICIAL USE ONLY


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