IE Circular No. 81-01, Design Problems Involving Indicating Pushbutton Switches Manufactured by Honeywell Incorporated
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
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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:
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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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Page Last Reviewed/Updated Tuesday, March 09, 2021