Bulletin 80-20: Failures of Westinghouse Type W-2 Spring Return to Neutral Control Switches
SSINS No.: 6820
Accession No.:
8006190023
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
July 31, 1980
IE Bulletin No. 80-20
FAILURES OF WESTINGHOUSE TYPE W-2 SPRING RETURN TO NEUTRAL CONTROL SWITCHES
By letter dated June 18, 1980, Commonwealth Edison Company submitted
Licensee Event Report No. LER 50-295/80-24 to the NRC describing a
malfunction of a Westinghouse Type W-2 control switch at the Zion Generating
Station, Unit 1. The malfunctioning switch is a three position spring return
to neutral switch. Although the switch was in its proper neutral position
when it malfunctioned, its neutral contacts failed to close properly thereby
preventing the automatic start of 1A Service Water Pump.
Subsequent tests conducted on the malfunctioning switch revealed that
contact closure was intermittent with the switch in the neutral (or "Auto
Start") position. Other tests conducted on identical switches from spares
and from Unit 2 equipment disclosed two additional switches with a tendency
for intermittent contact closure.
A review of this matter by Westinghouse led to the issuance of NSD Technical
Bulletin No. NSD-TB-80-9 to the utility owners of all Westinghouse operating
plants. The recommendations contained in the Westinghouse technical bulletin
include: (i) testing the neutral position contacts of the subject W-2
switches for continuity, and (ii) rewiring of the indicating light circuit
to permit the early detection of a neutral contact failure as shown in
Figure 1.
Depending on how the indicating light circuit is wired, loss of continuity
thru the neutral position contact of a W-2 switch could remain undetected
until the equipment associated with the switch were called upon to operate.
Since such a failure would be equivalent to by-passing the system associated
with the switch, consideration should be given to rewiring the switches used
in safety-related applications as shown in Figure 1. Such rewiring would
provide an acceptable means for detecting contact failure, provided the
indicating light is in the control room and readily visible by the operator.
If the indicating light is not so located, consideration should be given to
annunciating the neutral position contact failures at the control room to
alert the operator of the inoperable status of a safety-related system. In
addition, consideration should be given to adding redundant contacts to the
W-2 switches or to replacing the W-2 switches with others having a more
positive contact wiping action.
ACTIONS TO BE TAKEN BY LICENSEES AND HOLDERS OF CONSTRUCTION PERMITS:
1. Determine whether Westinghouse Type W-2 control switches with spring
return to neutral position are used in safety-related applications at
your facility. If so, identify the safety-related systems using these
.
IE Bulletin No. 80-20 July 31, 1980
Page 2 of 2
switches and the total number of switches so used. If no such switches
are used in your facility, you should indicate that this is the case
and ignore the remaining questions.
2. Licensees of operating plants using Type W-2 spring return to neutral
control switches in safety-related applications shall perform
continuity tests on all such switches. These tests shall be performed
with the switch operator in the neutral position and completed within
ten (10) days of the date of this bulletin. In addition, this
continuity test shall be repeated at least every thirty-one (31) days
after the initial test and after each manipulation of the switch from
its neutral position. These continuity tests may be discontinued
subsequent to implementing the longer term corrective measures
described below.
3. Licensees of operating plants and holders of construction permits shall
describe the longer term corrective measures planned and the date by
which such measures will be implemented by actual installation or by
design change, as appropriate. As a minimum, the longer term corrective
measures should include rewiring the indicating light as shown in
Figure 1 provided the light is readily visible to the control room
operator. If not, failures of the neutral position contacts should be
annunciated in the control room.
A report addressing the above matters, including the number of failures
detected during the first series of tests and the safety-related systems
involved, shall be submitted to the director of the appropriate NRC regional
office within forty-five (45) days of the date of this bulletin. A copy of
the report shall be forwarded to the Director, Division of Reactor
Operations Inspection, Office of Inspection and Enforcement, Nuclear
Regulatory Commission, Washington, D. C. 20555.
Approved by GAO, B180225 (ROO72); clearance expires 7/31/80. Approval was
given under a blanket clearance specifically for identified generic
problems.
Enclosure:
Figure 1
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