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Information Notice No.80-13 – General Electric Type SBM Control Switches Defective Cam Followers
SSINS No.: 6870 Accession No.: 8002280650 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 April 2, 1980 Information Notice No. 80-13 GENERAL ELECTRIC TYPE SBM CONTROL SWITCHES DEFECTIVE CAM FOLLOWERS Description of Circumstances: This Information Notice alerts licensees and holders of construction permits of a potential defect in the cam followers of General Electric (GE) Type SBM control switches. Based on preliminary information, it appears that the defect is limited to switches manufactured prior to 1976 with cam followers of polycarbonate material, such as Lexan. In brief, the problem is initiated by exposing such polycarbonate material to hydrocarbons. Such exposure leads to severe cracking having a rock salt appearance which ultimately could progress to mechanical failure. It has been determined that such exposure has occurred during fabrication and could occur while performing maintenance (e.g. cleaning the contacts). On February 22 and March 10, 1980 we were informed that SBM switches with defective cam followers had been found at Diablo Canyon Unit 1 and at the Cooper Station, respectively. Although the information was preliminary and sketchy, the problem is a long-standing one for which GE has issued "Service Information Letters" to its BWR customers. The problems associated with such switches, however, are not restricted to GE customers as evidenced by the Diablo Canyon case. Furthermore, these switches have a broad range of application. For example, the defective switches at the Cooper Station were used principally as hand control switches, most of which were located in the control room. In contrast, those at Diablo Canyon Unit 1 were used as auxiliary contacts on the 4KV and 12KV "Magna Blast" circuit breakers, with three SBM switches used per breaker: (1) a breaker mounted auxiliary switch, (2) a cell mounted auxiliary switch, and (3) a cell interlock switch. This information is provided as notification of a possibly significant matter that is still under review by the NRC staff. It is expected that recipients will review the information for possible applicability to their facilities. No specific action or response is requested at this time. If you have questions regarding this matter, please contact the Director of the appropriate NRC Regional Office.
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