Bulletin 79-28: Possible Malfunction of NAMCO Model EA180 Limit Switches at Elevated Temperatures
SSINS No.: 6820 Accession No.: 7910250505 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 December 7, 1979 IE Bulletin No. 79-28 POSSIBLE MALFUNCTION OF NAMCO MODEL EA180 LIMIT SWITCHES AT ELEVATED TEMPERATURES Description of Circumstances: The NRC has been recently advised through a 10 CFR 21 report from NAMCO Controls that a malfunction of a NAMCO Model EA180 stem mounted limit switch (SMLS) occurred at the Cooper Nuclear Station. Investigation into the switch failure by the licensee revealed yellow and brown "crystal-like" resin deposits on the internal components of the switch. The affected switch is located inside the drywell containment at this facility and was being used as the replacement switch for an unqualified SMLS previously identified in IE Bulletin Nos. 78-04 and 79-01. According to the manufacturer, the problem was traced to a batch of top cover gaskets of which some were over-impregnated and insufficiently heat cured. It has been determined that this condition can leave an uncured residue of "Loctite" in the gasket, which vaporizes at sustained temperatures above 175oF. To correct the problem, the manufacturer has revised production techniques,beginning September 1979 in order to better control the impregnation process and to properly heat cure the gaskets following impregnation. This problem is unique to all NAMCO Model EA180 series switches received by licensees after March 1, 1979. According to the manufacturer, the suspect switches can be identified by checking the date code which is a 4 digit number stamped on the conduit boss of the switch housing. NAMCO recommends that any EA180 series switch with a date code between 02-79 through 08-79 should have its top cover gasket replaced. Also, licensees should request from their suppliers of equipment on which NAMCO EA180 series switches are used that they check their inventory and replace top cover gaskets on switches date coded between 02-79 through 08-79. The enclosed letter from NAMCO further describes the high-temperature environmental problem with the top cover gaskets used in their EA180 switches and provides recommendations to correct the problem. According to NAMCO, this letter has been sent to each customer who was shipped EA180 switches between February 21, 1979, and August 24, 1979. Action to be Taken by Licensees of Power Reactor Operating Facilities and @ Holders of Construction Permits: 1. Determine if your facility has installed or plans to install NAMCO EA180 switches in any safety-related equipment located inside or outside containment, including valve position indicating circuitry related to containment isolation valves. . IE Bulletin No. 79-28 December 7, 1979 Page 2 of 2 2. If such switches are identified, examine the four digit number stamped on the conduit boss of the switch housing. If this number falls between 02-79 and 08-79, replace the top gasket of the switch in accordance with the manufacturer's recommendations provided in the enclosed letter. 3. Submit your plans and programs, including schedules for corrective action, regarding your findings in response to Items l and 2 above. 4. Provide the response in writing within 30 days for facilities holding an operating license and within 60 days for those holders of construction permits. Reports should be submitted to the Director of the appropriate NRC Regional Office and a copy should be forwarded to the U. S. Nuclear Regulatory Commission, Office of Inspection and Enforcement, Division of Reactor Operations Inspection, Washington, D.C. 20555. Approved by GAO, B180225 (R0072); clearance expires July 31, 1980. Approval was given under a blanket clearance specifically for identified generic problems. Attachment: Extract of NAMCO Controls Letter dated 8/30/79
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021