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

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Impact of Non-Safety Electrical Support System Vulnerabilities on Safety Systems
ML082730593
Person / Time
Issue date: 11/24/2008
Revision: 0
From: Dorman D H, Shea J W
NRC/NMSS/FCSS, NRC/RGN-II/DFFI
To:
References
IN-08-021
Download: ML082730593 (4)
v • d • e


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

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:

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)

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
  • 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
  • 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
  • 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

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 2005-15, "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 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

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

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 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

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

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/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


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