United States Nuclear Regulatory Commission - Protecting People and the Environment

IE Circular 76-04 - Neutron Monitor and Flow Bypass Switch Malfunctions


                              UNITED STATES 
                         WASHINGTON, D. C. 20555 
                            September 29, 1976 

J. P. O'Reilly, Director, Region I 
N. C. Moseley, Director, Region II 
J. G. Keppler, Director, Region III 
E. M. Howard, Director, Region IV 
R. H. Engelken, Director, Region V 


Enclosed is IE Circular No. 76-04 for distribution to all boiling water 
reactor facilities with an operating license or construction permit. 

This Circular should be forwarded by mail or other means within three 
working days of receipt of this memorandum by your office. 

                                        Dudley Thompson, Acting Director 
                                        Division of Field Operations 
                                        Office of Inspection and Enforcement

1.   Draft letter to 
2.   IE Circular 76-04
     dated 9/29/76
     "Neutron Monitor
     and Flow Bypass
     Switch Malfunctions"

(Addressees:  Reactor Facilities OL and CP Holders) 


The enclosed Circular No. 76-04 is forwarded to you as a matter concerning a 
possible generic problem relating to reactor safety systems and components. 

Any questions regarding this Circular should be directed to this office. 


                                        (Director, Regional Office) 

Circular No. 76-04 

IE Circular No. 76-04                            Date:  September 29, 1976 



Defective Neutron monitoring bypass switches have been experienced by 
General Electric during fabrication of control panels which were designated 
for shipment to nuclear power plants.  According to GE, switch malfunctions 
of this type also were reported from nuclear power plants following their 
initial finding.  The types of malfunctions experienced were: 

1.   Failure to move to a positive position. 

2.   Double contact operation causing an intermittent double bypass action. 

The cause of the bypass switch malfunctioning has been identified by the 
General Electric Company as improper fabrication (an inadequate weld of 
parts of the switch mechanism).  This phenomenon occurs after numerous 
bending motions and results in improper switch alignment, referred to by GE 
as "metal creep." 

Portions of a GE service letter containing information about these bypass 
switches is attached to this Circular.  Further information regarding this 
problem can be obtained from General Electric Company, 175 Curtner Avenue, 
San Jose, California 95125. 


For all boiling water reactor facilities with an operating license or 
construction permit: 

1.   Describe any malfunction experienced by your facility regarding these 
     switches.  Include in your response the approximate date of failure and
     any corrective measure taken to resolve the failure. 

2.   If you have received the attached general Electric service letter (SIL 
     111, Rev. 1, dated August 29, 1975), describe the actions taken 
     regarding corrective measures to resolve the bypass control switch 
     problem as discussed in the attached GE service letter.  Include in 
     your response your means of testing this circuitry to assure 

3.   If you have not received General Electric SIL 111, Rev 1, describe the 
     actions planned if switches of the type described in the attached 
     General Electric service letter are in use of planned for use in 
     safety-related systems at your facility.  Include in your response your 
     means of testing this circuitry to assure operability. 
Reports from facilities with operating licenses should be submitted within 
60 days after receipt of this Circular, and reports from facilities with 
construction permits should be submitted within 90 days after receipt of 
this Circular.  Your report should include the date when the above actions 
were or will be completed. 

Reports should be submitted to the Director of the NRC Regional Office and a 
copy should be forwarded to the NRC, Office of Inspection and Enforcement, 
Division of Reactor Inspection Programs, Washington, D. C. 20555. 

Approval of NRC requirements for reports concerning possible generic 
problems has been obtained under 44 U. S. C. 3512 from the U.S. General 
Accounting Office.  (GAO Approval B-180255 (R0072), expires 7/31/77). 


Extract from General Electric SIL 111, Rev. 1. 

                                                         Page 1 of 2 pages 

Extract from General Electric SIL 111, Rev. 1: 


General Electric has learned of a "metal creep" phenomenon which exists 
within the joystick operators of certain control room switches.  These 
switches are used at most operating GE/BWR plants in the Source Range 
monitor (SRM), Intermediate Range Monitor (IRM), Average Power Range Monitor 
(APRM) and Rod Block Monitor (RBM) Systems.  The switches are also used as 
flow bypass switches and in other applications. "Metal creep" is a condition 
which occurs in metal after numerous bending motions. This causes the metal 
to expand slightly.  The problem of "metal creep" with the joystick operator 
can result in improper switch alignment.  This can cause the switch to make 
multiple contacts (characterized by two or more channels being bypassed 
simultaneously).  Also, the joystick handle may appear to be in a neutral 
position while actually the switch contacts (due to "metal creep") are in a 
bypass condition. 

General Electric recommends that the bypass position be verified by the 
channel by pass indicator light and/or a computer run whenever these 
switches are operated.  General Electric also recommends replacement of both 
the switch and operator with improved components if problems are 
encountered. The replacement switches will vary from one generation of GE 
BWR to another. The physical description should include the number of 
contact blocks in the switch; the presence or absence of physical barriers 
between the contact blocks; and whether or not the switch is enclosed in a 
metal box.  The new switches contain both physical barriers and a metal 
switch enclosure.  The part numbers given below may be of assistance in 
determining your particular requirements: 

                                                         Page 2 of 2 Pages 

     New Part No.             Old Part No.             Where Used 

     193B1100G003             193B1100G001             APRM
     193B1100G004             193B1100G002              IRM
     158B7191G008                                       SRM 

To provide additional assurance that the RBM and flow bypass switches do not
become improperly aligned due to metal creep, GE recommends implementing the
wiring change given in the table below. 

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