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