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 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 

UNITED STATES 

NUCLEAR REGULATORY COMMISSION 

OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS 

WASHINGTON, D.C. 20555
IN 2008-21 

Page 2 of 4 

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 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 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 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 switchgear. Short term and long 

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

Accession No. ML050620142) 
IN 2008-21 

 Page 3 of 4 

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) 

• IN 2005-21, “Plant Trip and Loss of Preferred AC Power From Inadequate Switchyard 

Maintenance” (ADAMS Accession No. ML051740051) 
IN 2008-21 

Page 4 of 4 

• 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 

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 

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 2008-21 

Page 4 of 4 

• 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 

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 

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