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Information Notice No. 93-26: Grease Solidification Causes Molded-Case Circuit Breaker Failure to Close
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 April 7, 1993 NRC INFORMATION NOTICE 93-26: GREASE SOLIDIFICATION CAUSES MOLDED CASE CIRCUIT BREAKER FAILURE TO CLOSE Addressees All holders of operating licenses or construction permits for nuclear power reactors. Purpose The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert addressees to a problem with a 400-amp frame, 600 Vac molded case circuit breaker manufactured by General Electric Corporation (GE) (Part No. TJK436Y400) which failed to close when required due to grease solidification. 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. Description of Circumstances On March 26, 1992, an engineered safety feature actuated at the Nine Mile Point Nuclear Station Unit 2 because of the loss of output power from an uninterruptible power supply (UPS) while the loads were being transferred from UPS power to the maintenance supply power. During the transfer, the maintenance supply output circuit breaker (CB-4) failed to close causing a loss of power to the standby gas treatment system radiation monitoring cabinet, a false-high radiation signal, a group 9 primary containment isolation, the loss of a control room fire panel annunciator, and a loss of communication between the radiation monitoring system computer and non-Class 1E radiation monitors. The operator immediately took corrective action to manually close circuit breaker CB-4 and restore the UPS loads. The UPS loads lost power for approximately 12 minutes during the event. Discussion Niagara Mohawk Power Corporation, the licensee for Nine Mile Point 2, determined that the cause of the failure of circuit breaker CB-4 to close was that the grease used at the pivot points inside the breaker had dried out and solidified. When the grease dried out, it caused increasing friction and gouging at the metal-to-metal contact areas. This friction caused the breaker to become increasingly more difficult to close, until, finally, the breaker would not close at all. The licensee located all breakers of the same make, model, and year as the one that failed and scheduled their replacement. 9304010146 . IN 93-26 April 7, 1993 Page 2 of 2 GE has stated that all molded case circuit breakers manufactured prior to 1985 used a soap-based or clay-based grease that could solidify with age, and that they recommend field testing to identify such solidification. Since 1985, GE has replaced the soap-based and clay-based grease with a synthetic grease that does not dry out and solidify with age. However, it is possible that the older molded case circuit breakers using the clay-based and soap-based grease may still be used at other plants and could result in similar failures. This information notice requires no specific action or written response. If you have any questions about the information in this notice, please contact the technical contact listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager. ORIGINAL SIGNED BY Brian K. Grimes, Director Division of Operating Reactor Support Office of Nuclear Reactor Regulation Technical contact: Mark D. Pratt, NRR (301) 504-2701 Attachment: List of Recently Issued NRC Information Notices .
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