United States Nuclear Regulatory Commission - Protecting People and the Environment


                                                          SSINS No.: 6830  
                                                          Accession No.:   
                                                          8008220280       
                                                          IEC No. 81-01    

                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT 
                          WASHINGTON, D. C. 20555 
                                     
                              January 23, 1981 

IE CIRCULAR NO. 81-01:   DESIGN PROBLEMS INVOLVING INDICATING PUSHBUTTON 
                         SWITCHES MANUFACTURED BY HONEYWELL INCORPORATED 

Background: 

By letter dated September 18, 1980 (J. M. Curran to R. H. Engelken), 
Southern California Edison Company (SCE) notified NRC of design problems 
involving certain indicating pushbutton switches. The subject switches are 
of the type designated as Series 2 indicating pushbutton switches that are 
manufactured by the Micro Switch Division of Honeywell Incorporated. The 
switches identified by SCE as having design deficiencies are used on the 
containment isolation panels at San Onofre Unit 1 (Docket No. 50-206). 

SCE identified two problems with the subject switches, both of which 
manifest themselves during relamping: (1) a short circuit may be induced; 
and (2) the circuit controlled by the switch may inadvertently be actuated. 
Although the specificity of this circular is restricted to the previously 
mentioned Series 2 switches the deficiencies cited may be common to other 
indicating pushbutton switches. Accordingly, holders of operating licenses 
and construction permits should scrutinize the design of other indicating 
pushbutton switches in their facilities for susceptibility to the above 
problems. 

By letter dated October 10, 1980 (J. G. Haynes to R. H. Engelken), SCE 
submitted a detailed followup report addressing the defective switches. 
Sections of the SCE report containing relevant information have been 
excerpted and included in the paragraphs that follow. Sections so excerpted 
are identified by quotation marks. 

Discussion: 

The SCE report provided the following details of the problems previously 
mentioned: 

     "1.  The design of indicating pushbutton switches is such that during 
          insertion of the lamp assembly into the switch housing, shorting 
          could occur between the metallic plunger and the energized 
          indicator lamp connection inside the switch assembly. Since the 
          metal plunger is connected to the cabinet ground through the 
          switch housing, the control circuit could be short circuited, 
          causing failure of the control circuit if it is energized. 
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                                                        IEC No. 81-01     
                                                        January 23, 1981  
                                                        Page 2 of 4       

     2.   The design of the lamp assembly is such that to lock the switch 
          into place after relamping will cause actuation of the switch 
          resulting in operation of the control circuit if it is energized. 
          Since the current containment isolation system operational design 
          requires that the power supply to the containment isolation panels
          remain energized during relamping, the potential exists for 
          operating containment isolation valves during the lamp 
          replacement." 

To circumvent the preceding problems, SCE, in cooperation with Honeywell 
Incorporated, is implementing the following corrective actions. 

     "1.  The metallic plunger is being redesigned to solve the short 
          circuit problem discussed in Item 1 above. The design modification 
          involves providing a plastic tip on the plunger. The plastic tip 
          will provide isolation between the metallic plunger and energized 
          indicator lamp connection inside the switch assembly and this will 
          avoid short circuit problems. A prototype modified switch assembly 
          was received on September 20, 1980 and successfully tested. 
          Accordingly, the manufacturer is developing the necessary tooling 
          for production purposes. It is expected that the modified switch 
          assemblies can be delivered and installed prior to return to power 
          operation from the current outage. 

     2.   The indicating pushbutton lamp assembly system is being redesigned
          to solve the switch actuation problem discussed in Item 2 above. 
          The design modification will permit relamping with the power 
          supply energized, without causing switch actuation. It is expected 
          that the system will be redesigned and the current switches 
          replaced during the next scheduled cold shutdown of sufficient 
          duration following return to power operation from the current 
          outage." 

In addition, SCE has instructed its station personnel on procedural steps to
be followed when changing lamps. The procedural steps currently in effect at
San Onofre Unit 1 for relamping the indicating push button switches address 
the potential for shorting or for inadvertently actuating the control 
circuit as follows: 

     "1.  Containment Isolation Valves on Non-essential Systems 

          All automatic containment isolation valves are included in this 
          category. When replacement of a burned out lamp is necessary, the 
          power supply of the circuit of the valve will be opened and the 
          associated valve will close if open or will be de-energized in the
          closed position if already closed. The burned out lamp will be 
          replaced and the power supply to the circuit will be closed 
          permitting the valve to be reopened or re-energized in the closed 
          position. 

     2.   Remote Manual Containment Isolation Valves on Essential Systems 

          The systems in this category include the Chemical Volume and 
          Control Letdown System, Reactor Coolant Pump Seal Water Return 
          System, Turbine Plant Cooling Water Supply and Return System, and 
          Pressurizer Relief 

.

                                                        IEC No. 81-01     
                                                        January 23, 1981  
                                                        Page 3 of 4       

          Tank Nitrogen Supply System. The containment isolation valves on 
          these systems are normally open during operation and may be 
          required to be open during accident conditions. 

          If it is necessary to replace burned out lamps after the metallic 
          plunger has been redesigned as described in corrective action l 
          above, the following steps will be taken: 

          1.   The touch plate with the burned out lamp will be removed and 
               lamps replaced. 

          2.   The glass cover on the HFA relay (panels behind north 
               vertical board) associated with the valve in question will be 
               removed and the relay held in place by depressing the 
               insulated portion of the spring loaded relay plunger. 

          3.   The touch plate with the replaced lamps will be inserted into
               the switch chassis. 

          4.   The "open" switch of the valve in question will be depressed 
               to assure that the circuit has been reset and the glass cover
               replaced on the HFA relay." 

     "If it is necessary to replace burned out lamps before the metallic 
     plunger is redesigned, the replacement will be performed during an 
     outage of sufficient duration when the affected system and valve can be
     removed from service. At that time, the procedural steps to be followed
     are identical to those established for the automatic containment 
     isolation valves on nonessential systems discussed above. Until such 
     time as the lamp can be replaced, the position of the affected valve 
     can be determined by examining the system flow, pressure and 
     temperature process instrumentation." 

Recommended Actions for Holders of Construction Permits or Operating 
Licenses: 

1.   Determine whether your facility uses the subject Series 2 indicating 
     pushbutton switches in any safety-related function. If there are no 
     indicating pushbutton switches of this type in your facility, you need 
     not pursue this matter further. 

2.   If the subject switches are used to perform safety-related functions at
     your facility, either replace them with qualified units or modify them 
     to eliminate the deficiencies. Holders of operating licenses should 
     take the appropriate action as soon as practical; construction permit 
     holders should take the appropriate action prior to startup. (If the 
     switches are to be modified, contact Honeywell Incorporated for 
     assistance.) 

3.   Until the appropriate corrective action is completed, the following 
     interim measures should be taken: 

.

                                                        IEC No. 81-01     
                                                        January 23, 1981  
                                                        Page 4 of 4       

     a.   If the design of the affected equipment permits its switch 
          assembly to be deenergized for relamping, verify that the 
          procedures specify that power is to be removed from the switch 
          assembly during relamping. If the procedures do not so specify, 
          revise them to include such a provision. 

     b.   If the design of the affected equipment does not permit its switch
          assembly to be deenergized for relamping, verify that the operator
          can determine the status of the affected equipment by alternate 
          means. Towards this end, implement procedures to enable the 
          operator to determine the status of the affected equipment by 
          alternate means (e.g., acceptable method for inferring the 
          position of a valve could include system flow, pressure, or 
          temperature measurements). If alternate status indication methods 
          are not available, relamping should be deferred until the next 
          outage during which time the affected equipment can be removed 
          from service. However, during the resulting blind time, rigid 
          administrative controls should be implemented to provide the 
          operator with reliable status information. 

No written response to this circular is required. If you require additional 
information with regard to this subject, please contact the appropriate NRC 
Regional Office. 

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