United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 78-04: Environmental Qualification of Certain Stem Mounted Limit Switches Inside Reactor Containment

                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT 
                          WASHINGTON, D. C. 20555 

                             February 21, 1978 

                                                     IE Bulletin No. 78-04 

ENVIRONMENTAL QUALIFICATION OF CERTAIN STEM MOUNTED LIMIT SWITCHES INSIDE 
REACTOR CONTAINMENT 

Description of Circumstances: 

As a result of a recent review by Westinghouse of the seismic and 
environmental qualifications of the electrical circuitry used for valve 
operation, certain stem mounted limit switches (SMLS) associated with 
various safety related valves were found not to be environmentally qualified 
for loss of coolant accident (LOCA) conditions. The switches in question are 
installed on certain motor operated valves and certain air-operated valves 
located in primary containment. The functions of these valves provide either 
containment isolation or emergency core cooling system (ECCS) alignment 
during accident conditions. 

Westinghouse has stated that for air operated valves the SMLS function is to
provide "latch-in" capability to the actuation control circuitry of the 
valve. It therefore is designated as safety-related and must receive seismic
and environmental qualification. 

The concern arises if the SMLS contacts short circuit during LOCA 
conditions. If this occurs and if the valve control switch is in the "AUTO" 
position (and control air is available to the valve operator), the valve 
will move from its post accident position to the normal operating position 
when either the safety injection or containment isolation signal is reset. A 
limited number of the switches are also used in safety related motor 
operated valve circuits in Westinghouse designed plants. 

The attached Westinghouse Technical Bulletin, NSD-TB-77-13 issued on 
September 30, 1977, further describes the problem and provides suggestions 
for correcting the problem in air-operated valve actuation circuitry. One of
the corrective actions considered by Westinghouse involves replacement of 
the switch with a switch that is environmentally qualified. An alternative 
corrective action utilizes a circuit modification to the "latch-in" feature 
associated with the air-operated valve circuitry so that no adverse affect 
on valve operation can occur during 



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IE Bulletin No. 78-04                                   February 21, 1978 

post accident conditions. For example, VEPCO has initiated a modification to
the valve control circuitry at North Anna to remove the SMLS contacts from 
the valve operation circuitry. 

The SMLS in question is identified as NAMCO Model D2400X or EA-170-302 SNAP 
LOCK. NAMCO can provide qualified switches to replace unqualified ones upon 
request from the user. Because all NAMCO SNAP LOCK type switches have been 
seismically qualified by tests, only environmental qualification is a 
concern in this issue. This problem ma be generic for all power reactor 
facilities with an operating license or a construction permit. 

Action to be Taken by Licensees and Permit Holders: 

For all power reactor facilities with an operating license or a construction
permit: 

1.   Determine if your facility utilizes or plans to utilize NAMCO D2400X or
     EA-170--302 SNAP LOCK switches in any safety related equipment in the 
     primary containment, including the valve control circuitry previously 
     discussed. 

2.   If any such applications are identified, review these applications to 
     determine the adequacy or qualification testing for these switches and 
     submit the qualification documentation or references to NRC for review.

3.   If evidence is not available to support a conclusion of adequacy, 
     submit your plans and programs, including schedules, for corrective 
     action. 

4.   Provide your response in writing within 30 days for facilities holding 
     an operating license and within 60 days for those facilities with a 
     construction permit. Reports should be submitted to the Director of the
     appropriate NRC Regional Office and a copy should s be forwarded to the
     U. S. Nuclear Regulatory Commission, Office of Inspection and 
     Enforcement, Division of Reactor Operations Inspection, Washington, 
     D.C. 20555. 




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IE Bulletin No. 78-04                                   February 21, 1978 

Approved by GAO, B180225 (R0072); clearance expires 7/31/80. Approval was 
given under a blanket clearance specifically for identified generic 
problems. 

Attachment: 
W Technical Bulletin 
   NSD-TB-77-13  




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