Information Notice 2005-21, Plant Trip and Loss of Preferred AC Power From Inadequate Switchyard Maintenance
| ML051740051 | |
| Person / Time | |
|---|---|
| Issue date: | 07/21/2005 |
| Revision: | 0 |
| From: | Hiland P L NRC/NRR/DIPM/IROB |
| To: | |
| Koshy T, NRR/DE/EEIB, 415-1176 | |
| References | |
| IN-05-021 | |
| Download: ML051740051 (4) | |
July 21, 2005
NRC INFORMATION NOTICE 2005-21: PLANT TRIP AND LOSS OF PREFERRED ACPOWER FROM INADEQUATE SWITCHYARD MAINTENANCE
ADDRESSEES
All holders of operating licensees for nuclear power reactors, except those who havepermanently 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 to informaddressees about loss of power events as a result of inadequate preventive and corrective maintenance practices on switchyard breakers and current transformer It is expected that recipients will review the information for applicability to their facilities and consider actions, asappropriate, to avoid similar problem However, suggestions contained in this information notice are not NRC requirements; therefore, no specific action or written response is required.
DESCRIPTION OF CIRCUMSTANCES
On May 5, 2004, Dresden Unit 3 was at full power and Dresden Unit 2 was shutdown when anautomatic reactor scram and a subsequent loss of offsite power event occurred during activities to reconfigure breakers in the 345 kV switchyar Operations personnel manually opened switchyard breaker 8-15 in accordance with the switching orde However, when the A and B phases opened, the C phase of switchyard breaker 8-15 failed to fully open within the required time. This failure produced current imbalances in Unit 2 and Unit 3 switchyard ring busses (tied together through a breaker), which led to the opening of several other switchyard breaker Unit 3 scrammed due to turbine load reject, and offsite power was lost to the Unit 3 safety- related emergency core cooling system (ECCS) busse The failed breaker was an I-T-E Imperial Corporation (current vendor ABB) sulfur hexafluoride (SF6) gas circuit breaker (type 362GA). This breaker used independent pole operators for each of the three phase The breaker was built and installed in the Dresden 345 kV switchyard in the late 1970's.On May 6, 2004, the licensee and personnel of the transmission and distribution company,Exelon Energy Delivery (EED), discovered that ABB, the current breaker vendor, had issued a product advisory in July 2003 for I-T-E Imperial Corporation GA and GB breakers to warn that the operating mechanisms may experience delayed trip or in some cases failures to trip due to age and application related problem In addition, the advisory noted that the breakers at highest risk were those operated less than twice per yea The product advisory recommendedthat the operating mechanism in high-risk applications be rebuilt using new trip latch mechanism kits at the earliest convenienc While disassembling the trip latch mechanism of Breaker 8-15, EED and licensee personneldiscovered that the sealed bearing for the trip latch mechanism did not roll freely. The failure of the sealed bearing to roll freely, directly contributed to the failure of the C phase of Breaker 8-15 to open within the required tim The NRC special inspection team reviewed themaintenance history of Breaker 8-1 The last preventive maintenance on Breaker 8-15 was done on March 27, 2002, and included routine inspection, lubrication and maintenance, acontact resistance test, and a travel timing tes The inspection team noted that the breaker failed the timing test on the C Phase. The breaker was last cycled in October 2002 and thenremained in the closed position until May 5, 2004.The NRC inspection team noted that the EED procedure stated that the breaker should belubricated after a failed timing tes However, the vendor manual stated that, the operating mechanism should be disassembled and cleaned and lubricated when the operating mechanism showed signs of difficult or sluggish operatio In addition, the manual stated that under ordinary circumstances, the life of the grease in sealed bearings should be at least 10 years and that if oxidation of the lubricant made the bearing sluggish, the bearing must bereplace The EED preventive maintenance program and procedures for breakers did not include routine replacement of worn out breaker part In addition, the EED maintenance procedures did not instruct maintenance personnel to disassemble sluggish operating mechanisms to check for degraded bearings, nor did the procedures specify the appropriate lubricants for the various parts of the breaker. On June 12, 2002, with DC Cook Unit 1 at approximately 68% power and Unit 2 at 100%power, an emergency alert condition was entered after a catastrophic failure and resultant fire of a current transformer for the 345 kV switchyard L breake The catastrophic failure of the current transformer and the subsequent switchyard switching actions resulted in the loss of the preferred offsite power source to Units 1 and On June 19, 2002, the NRC special inspectionteam reviewed the licensee's preventive maintenance program for 345 kV switchyard current transformer The vendor's preventive maintenance recommendations included annualinspections and transformer oil analysis every 2 year The inspection team reviewed historical maintenance activities on the L breaker current transformers and determined that preventivemaintenance activities were last done in October 199 The periodicity of preventive maintenance activities was consistent with American Electric Power (AEP) system guidelines,but not with the vendor's recommendation Additionally, the licensee did not periodicallyperform several vendor-recommended tests, including tests of oil dielectric strength and oil acidfactor, and a measurement of the resistance of the current transformer primary (to compare with the results in the test report). During followup discussions, licensee personnel stated that the types of testing performed and the testing frequencies were based on AEP systemoperating experience rather than vendor recommendation Licensee personnel were unable to readily provide specific operating experience data that justified the 4-year preventivemaintenance testing frequenc Licensee personnel subsequently determined that there wereapproximately one hundred twenty six 345 kV current transformers in the AEP system similar indesign to the transformers located in the DC Cook 345 kV switchyar Since 1990, there have been two catastrophic failures (both associated with the D. C. Cook 345 kV switchyard L breaker). No current transformers of this type had been removed from service based on preventive maintenance testin Following the June 12, 2002, current transformer failure, AEP collected oil samples from theD.C. Cook 345 kV switchyard breaker current transformers for analysi The oil analyses were completed 3 months before the normal schedule as part of the licensee's extent-of-conditionevaluatio During the oil sampling, AEP personnel discovered that two current transformersfor N1 switchyard breaker were last sampled in September 1998, with gas analyses results significantly above the acceptable leve Based on this result, licensee replaced the N1 breaker current transformers and returned the breaker to service on June 29, 200 The AEP systemoperating experience data did not justify a less frequent analysis than recommended by the vendor.
DISCUSSION
The discrepancies, between the licensee's maintenance practices for switchyard breaker andcurrent transformers and the vendor recommendations, contributed to the inadvertentswitchyard breaker trips that resulted in a plant trip and loss of offsite power (LOOP) to safety busse Unnecessary plant trips and LOOP events could be reduced by following vendor recommendations with feedback from operating experience to determine the appropriate schedule and extent of maintenance.
CONTACT
This information notice requires no specific action or written respons Please direct anyquestions about this matter to the technical contact listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager./RA/Patrick L. Hiland, Chief Reactor Operations Branch Division of Inspection Program Management Office of Nuclear Reactor Regulation
Technical Contact:
Thomas Koshy, NRRAllan Barker, RIII301-415-1176630-829-9679 E-mail: txk@nrc.gov E-mail: arb3@nrc.govNRR Project Manager:Richard Laura, NRR301-415-1837 E-mail: ral1@nrc.govNote: NRC generic communications may be found on the NRC public Website,http://www.nrc.gov, under Electronic Reading Room/Document Collection Following the June 12, 2002, current transformer failure, AEP collected oil samples from theD.C. Cook 345 kV switchyard breaker current transformers for analysi The oil analyses were completed 3 months before the normal schedule as part of the licensee's extent-of-conditionevaluatio During the oil sampling, AEP personnel discovered that two current transformersfor N1 switchyard breaker were last sampled in September 1998, with gas analyses results significantly above the acceptable leve Based on this result, licensee replaced the N1 breaker current transformers and returned the breaker to service on June 29, 200 The AEP systemoperating experience data did not justify a less frequent analysis than recommended by the vendor.
DISCUSSION
The discrepancies, between the licensee's maintenance practices for switchyard breaker andcurrent transformers and the vendor recommendations, contributed to the inadvertentswitchyard breaker trips that resulted in a plant trip and loss of offsite power (LOOP) to safety busse Unnecessary plant trips and LOOP events could be reduced by following vendor recommendations with feedback from operating experience to determine the appropriate schedule and extent of maintenance.
CONTACT
This information notice requires no specific action or written respons Please direct anyquestions about this matter to the technical contact listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager./RA/Patrick L. Hiland, Chief Reactor Operations Branch Division of Inspection Program Management Office of Nuclear Reactor Regulation
Technical Contact:
Thomas Koshy, NRRAllan Barker, RIII301-415-1176630-829-9679 E-mail: txk@nrc.gov E-mail: arb3@nrc.govNRR Project Manager:Richard Laura, NRR301-415-1837 E-mail: ral1@nrc.govNote: NRC generic communications may be found on the NRC public Website,http://www.nrc.gov, under Electronic Reading Room/Document Collections.DISTRIBUTION: IN FileADAMS ACCESSION NUMBER: ML051740051OFFICEEEIB:DETech EditorOES:IROB:DIPMBC:EEIB:DENAMETKoshy(RLaura for PKleene) RALauraJACalvoDATE / /200507/05/200507/05/200507/18/2005OFFICETL:C:IROB:DIPMC:IROB:DIPMNAMEEJBenner (MJRoss-Leefor)PLHilandDATE07/19/200507/21/2005OFFICIAL RECORD COPY