. IEB 74-09 UNITED STATES ATOMIC ENERGY COMMISSION DIRECTORATE OF REGULATORY OPERATIONS REGION I 631 PARK AVENUE KING OF PRUSSIA, PENNSYLVANIA 19406 August 6, 1974 Consolidated Edison Company of New York, Inc. Docket No. 50-286 Attention: Mr. W. J. Cahill, Jr. Vice President 4 Irving Place New York, New York 10003 Gentlemen: The enclosed DRO Bulletin No. 74-9, "Deficiency in the General Electric Model 4KV Magne-Blast Circuit Breakers," is being sent to you relating experience with some of these circuit breakers at Vermont Yankee and Calvert Cliffs nuclear facilities. This information may have applicability to your facilities. Action on your part is identified in Section B of the enclosed Bulletin. Sincerely, James P. O'Reilly Director Enclosure: DRO Bulletin No. 74-9 cc: A. D. Kohler, Jr., Resident Construction Manager A. E. Upton, Esquire . Directorate of Regulatory Operations Bulletin 74-9 August 6, 1974 DEFICIENCY IN GENERAL ELECTRIC MODEL 4KV MAGNE-BLAST BREAKERS We have recently received information form the licensee of Calvert Cliffs Units 1 and 2 relating to circuit breaker malfunctions in engineered safety systems. These circuit breakers, General Electric Model 4KV safety Magne-Blast are used extensively at both PWR and BWR facilities. The malfunctions, which could negate operation of engineered safety system components, were attributed to an oversized roller trip bar and improper clearences of related guide holes and linkages. We have also received information from the licensee of Vermont Yankee Station describing an installation deficiency of the auxilliary switch assembly installed in the General Electric Model 4 KV Magne-Blast circuit breakers. Although the circuit breakers are similiar in model to the units used at Calvert Cliffs, they are of a different type and are used at both PWR and BWR facilities. Pertinent details relating to both problems are contained in Section A below, and the related action requested by this Bulletin is contained in Section B. A. Description of Circumstances Calvert Cliffs Units 1 and 2 On several occasions in the past, there had been unexplained "trip open" operations of several 4KV circuit breakers. On each occasion, the anomaly occurred immediately following an attempt to close the circuit breakers. Investigation into the problem disclosed that causes for failure were attributed to an oversized spring discharge roller bar located on the right side of the breaker cubicle and improper clearences in the roller bar guide hole and associated linkages. The purpose of the roller bar is to trip open the breaker unit in the event it is inserted into the breaker cubicule while in its closed position. However, the installed roller bars were found to be approximately 1/4" longer than the design length, causing interference with the breaker auxiliary switch linkage. Approximately 116 circuit breakers of the make and model describe herein and equipped with the faulty roller bars and the above mentioned clearence problem are used in the two nuclear units at this facility. Because we are requesting that you determine whether or not the subject breakers are used or are planned to be used at your facility the following details are provided for your information: . RO Bulletin No. 74-9 - 2 - Manufacturer: General Electric Co. Auxiliary Switch Assemblies in MC-4.76 Horizontal Drawout Metal Clad Switchgear with AMH-4.76-250 Breaker Vermont Yankee The licensee reported that while investigating a problem involving a station service water pump 4KV circuit breaker, an electrician noted that the breaker stationary auxiliary switch assembly rear mounting bolt had loosened and was disengaged from its mounting plate. The loose bolt is one of two bolts that assist in maintaining proper switch contact alignment. The loosening and disengagement of the tie bolt caused misalignment of the switch assemblies installed in forty-seven 4KV circuit breakers at this faccility found that all switch assemblies exhibited varying degrees of bolt loosening. Because we are requesting that you determine whether or not the subject devices are used or are planned to be used at your facility, the following details are provided for your information: Manufacturer: General Electric Co. Type: Metal Clad, M26 Swithgear (This switchgear has the auxiliary switch assembly mounted to it and may be used with a large number of different circuit breakers.) B. Action Requested It is requested that you determine whether safety related (Class IE) circuit breakers of the described makes and models are installed at your facilities and provide the RO Regional Office with your findings within 20 days from receipt of this bulletin. With regard to the problem at Calvert Cliffs Units 1 and 2, if the subject breakers are installed, please include in your response a description and the results of your program to determine if you have oversized roller trip bars installed and the scheduled completion date of your corrective actions. For facilities under construction, please inform us of your plans to assure that appropriate modification has been implemented in all safety related circuit breakers of the type described that have been or will be installed at your facility. With regard to the Vermont Yankee problem, it is requested that you ascertain the bolt tightness conditions of the switch assembly in question and include in your response a description and the results of your inspection program concerning these matters. It is also requested that you inform us of your plans regarding the long term verification of bolt tightness of the switch assemblies. . RO Bulletin No. 74-9 - 3 - Should you have any question concerning this matter, we will be pleased to discuss them with you.
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