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**UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555-0001**

October 15, 1998

**Addressees**

All holders of operating licenses for nuclear power reactors.

**Purpose**

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert addressees to inspectionfindings concerning inadequate preventive and corrective maintenance programs and corrective actions. It is expected thatrecipients will review the information for applicability to their facilities and consider actions, as appropriate, to avoidsimilar problems. However, suggestions contained in this information notice are not NRC requirements; therefore, nospecific action or written response is required.

**Background**

In 1997, failures of safety-related circuit breakers at nuclear power facilities prompted reactive inspections by the NRC.The staff is concerned about these failures because a common failure mode of safety-related circuit breakers couldsignificantly hamper a plant's ability to deal with a transient. This information notice will offer some insights gained fromthe findings of the reactive inspections.

In response to these recent events, the NRC is now conducting a series of inspections at some nuclear power plants,original equipment manufacturer (OEM) facilities, and third-party overhaul contractor shops to determine the present stateof medium-voltage and low-voltage metal clad circuit breaker maintenance and overhaul programs. At the conclusion ofthese inspections, the staff will evaluate the results, along with the progress made by the Electric Power ResearchInstitute's Nuclear Maintenance Applications Center (EPRI/NMAC) circuit breaker users groups and the Nuclear EnergyInstitute (NEI) task force, to determine whether further regulatory actions are needed.

The staff recognizes that the industry is working to improve the reliability of medium and low-voltage circuit breakers, asevidenced by the activities of the EPRI/NMAC circuit breaker users groups and the NEI Circuit Breaker Task Force. Thosegroups are working to issue preventive maintenance and overhaul guidance for breakers made by General Electric,Westinghouse, and Asea Brown Boveri (ABB).

**Description of Circumstances**

In 1997, three nuclear power plants were either forced to shut down or to extend an outage, and one plant consideredshutting down because a potential common failure mode called into question the operability of safety-related circuitbreakers. The NRC sent inspection teams to the four sites to review and evaluate licensee maintenance practices andcorrective actions. All of the breakers in the discussions that follow were manufactured by Westinghouse or GeneralElectric, but ABB product lines have also experienced similar problems over the last few years. Issues involving circuitbreaker maintenance and overhaul are germane to all manufacturers.

CLINTON POWER STATION

On August 5, 1997, Clinton Power Station was preparing to return to power after an outage when the A-train residual heatremoval (RHR) pump supply breaker did not open on demand when operators attempted to swap RHR pumps in theshutdown cooling mode. Only two weeks before this event, on July 22, 1997, the reserve auxiliary transformer (RAT)feeder breaker to the 4-kV bus for Division 1 failed to open when operators attempted to swap the bus feed to theemergency reserve auxiliary transformer. The failed breakers in both instances were Westinghouse Type DHP 4-kV metalclad circuit breakers. Because (1) there appeared to be a common failure mode, (2) the licensee corrective action for thefirst breaker failure did not prevent the second failure, and (3) there was a poor maintenance history, the NRC dispatchedan augmented inspection team (AIT) to the site and issued a demand for information (DFI) letter concerning the licensee'scorrective action program and its effectiveness in ensuring the operability and reliability of safety-related systems, andinforming the licensee that a response was required before the NRC would authorize a plant restart. The plant remains shutdown at this time.

The AIT concluded that both of the circuit breaker failures were caused by inadequate and inappropriate preventivemaintenance activities, and deficiencies in Clinton's corrective action program. The preventive maintenance program didnot include lubrication of all vendor-recommended areas, most notably in the main and arcing contacts. The licensee alsoused unapproved cleaning agents, which inadvertently removed vendor-applied lubricant, and then did not relubricate theaffected areas. The licensee also did not effectively evaluate the July 22 breaker failure. These combined deficienciesresulted in the introduction of a common failure mode for all of the safety-related 4-kV Westinghouse breakers at the plant.The licensee's investigation of the August 5 breaker failure was significantly more rigorous than the investigation into theJuly 22 failure had been. However, NRC prompting was necessary at times to ensure a thorough licensee investigation. Forexample, initially the licensee investigation focused on the lack of lubrication, and did not consider that the opening springscould have contributed to the failure. Subsequent review determined that although the lack of lubrication was the maincontributor to the RHR breaker failure, a bent and shortened kick-out spring also played a significant role. Refer to NRCInspection Report 50-461/97018 (Accession #9712040128) for further details.

INDIAN POINT 2 NUCLEAR POWER PLANT

On October 14, 1997, Consolidated Edison Company of New York voluntarily shutdown its Indian Point 2 Nuclear PowerPlant (IP2) because of concerns about the operability and reliability of its safety-related 480-V Westinghouse Type DB-50circuit breakers. The action was taken after experiencing recurring problems with these breakers to either close on demandor to remain closed.

An NRC inspection identified several weaknesses associated with the licensee's corrective maintenance, preventivemaintenance, and other corrective actions concerning circuit breakers. In June 1997, the licensee hired a contractor toperform a root-cause analysis. The contractor's report did not discuss all the possible failure modes and erroneouslyconcluded that the DB-50 breaker failures were caused by malfunctioning solid-state trip devices (Amptectors) andoperating mechanism binding caused by accumulated dust and dirt contaminating the mechanism's lubricant. Theinadequate root-cause analysis led to the occurrence of more failures, which eventually prompted the October shutdown.Before the plant shutdown, the licensee did not vigorously pursue a root cause after experiencing a breaker failure.Typically, a failed breaker would be removed from service and the preventive maintenance procedure would be performedto restore it to an operable status without identifying the cause of the problem.

Following the plant shutdown, the IP2 licensee conducted an extensive testing program to determine the root cause of thebreaker failures. High-speed video, static and dynamic closing coil current measurements, component displacements, andforce measurements were made, which identified several contributors to breaker failures. Refer to NRC Inspection Report50-247/97-13 (Accession #9802250110) for further details. The licensee has developed useful diagnostic tools that couldhelp in revealing or predicting breaker performance problems.

COOPER NUCLEAR STATION

On October 5, 1997, failure of a non-safety-related General Electric 4-kV (Magne-Blast) circuit breaker prompted theCooper licensee to review its breaker maintenance and overhaul program. The review identified 6 of 24 safety-related 4-kVbreakers that had not been overhauled during the 23 years of plant operation. The affected breakers included twoemergency diesel output breakers, two residual heat removal pump breakers, a service water pump breaker, and a 4-kV/480-V transformer supply breaker. The licensee initially considered shutting the plant down if the six safety-relatedbreakers were judged to be inoperable. Subsequent discussions with GE about the condition of these breakers determinedthat the breakers were in a degraded but operable condition. The licensee implemented an accelerated program to overhaulthe six breakers.

The NRC sent an inspection team to the site on October 20, 1997, to review the causes and circumstances associated withthis issue. The team found that the licensee experienced several problems with the GE Magne-Blast breakers in the late1980's and implemented a program to overhaul its safety-related 4-kV breakers, but for reasons unknown, the program wasterminated in 1994 with 6 of the breakers not being overhauled. The licensee's operating experience review program didnot include review of the vendor's service advice letters (SALs), which are issued to alert customers to changes inmaintenance recommendations or physical design changes made in subcomponent piece parts to address a specificidentified problem. In addition, licensee review of NRC information notices was narrowly focused and sometimes did notconsider the information provided in a specific notice as applicable to Cooper because of minor differences between themodel numbers discussed in the notice and the components used at Cooper. Several inconsistencies were identifiedbetween licensee maintenance procedures and vendor recommendations. The licensee did not have adequate justificationfor many of the identified inconsistencies. Refer to NRC Inspection Report 50-298/97018 (Accession #9712220092) forfurther details.

INDIAN POINT 3 NUCLEAR POWER PLANT

On December 18, 1997, at Indian Point 3 Nuclear Power Plant (IP3), an RHR pump breaker (Westinghouse Type DS-416)failed to open to disconnect the pump motor from its 480-V emergency electrical bus at the end of a surveillance run. Theelectrical bus was declared inoperable, which forced a plant shutdown. The NRC sent a special inspection team to the sitebecause of the potential generic implications. On December 22, 1997, during testing of additional breakers, another safety-related breaker was found to be potentially degraded.

Investigation of the failed RHR pump breaker found that factory-applied lubrication (poxylube) had been removed fromseveral locations on the operating mechanism during overhaul by a third-party contractor during refurbishment activities in1994. Neither the licensee nor the contractor knew about the use of poxylube because the information was consideredproprietary by the OEM and, as a result did not appear in any of the vendor's literature. The vendor's manual specifiessome preventive maintenance actions to be taken by the customer but recommends that the breaker be returned toWestinghouse for disassembly and overhaul of the operating mechanism.

The lack of lubrication was a primary contributor to the breaker failure but the licensee and Westinghouse discoveredanother anomaly during the investigation. With the pole shaft reset spring removed, some breakers could be made to lockup in the closed position. Normal operation of the breaker calls for the reset spring to be installed, but the spring wasremoved to facilitate testing of the failed breaker. The investigation found that a combination of wear, inadequatelubrication, and clearances in the linkage subcomponents (clevises, pins, and support points) could allow the pole shaft toovertravel and cause the breaker to lock up in the closed position when the reset spring was removed. It was discovered thatsome breakers overhauled by the OEM would also lock up in the closed position without the reset spring attached. Whilethis information is new to both the OEM and the licensee, it is not considered to be a defect in the breaker since the resetspring is attached during normal operation. See NRC Inspection Report 50/285 97-81 (Accession #9804080233) for details.

**Related Generic Communications**

Numerous information notices have been issued concerning lubrication of circuit breakers. It appears that ineffectivepreventive maintenance, including a lack of lubrication or inadvertent removal of factory-applied lubricant, continues to bea major factor in circuit breaker failures.

This information notice requires no specific action or written response. However, recipients are reminded that they arerequired to consider industry-wide operating experience (including NRC information notices) where practical, when settinggoals and performing periodic evaluations under Section 50.65, "Requirement for monitoring the effectiveness ofmaintenance at nuclear power plants," to Part 50 of Title 10 of the Code of Federal Regulations. If you have any questionsabout the information in this notice, please contact one of the technical contacts listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.

Attachment:  List of Recently Issued NRC Information Notices

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