Information Notice No. 84-47: Environmental Qualification Tests of Electrical Terminal Blocks
SSINS NO: 6835
IN 84-47
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
June 15, 1984
Information Notice No. NO 84-47: ENVIRONMENTAL QUALIFICATION TESTS OF
ELECTRICAL TERMINAL BLOCKS
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or
construction permit (CP).
This information notice is being issued to provide licensees and
construction permit holders with information pertaining to the results of a
recent NRC-sponsored environmental qualification methodology research test
conducted on electrical terminal blocks. This information notice also serves
as an early notification regarding the reduction of insulation resistance
values sustained by certain terminal blocks used in a Conax Electrical
Penetration Assembly during a design basis event simulation test.
It is expected that recipients will review the information for applicability
to their facilities. No specific action or response notice is required.
Description of Circumstances:
1. Additional information on NRC-sponsored test on terminal blocks In
1981, the NRC sponsored a research test on-terminal blocks to
investigate the insulator deterioration of the terminal blocks under
accident conditions. This test was conducted at the Sandia National
Laboratories (SNL) in Albuquerque, New Mexico. The test results of this
earlier test program were published in Information Notice No. 82-03.
The results then indicated that the performance of the terminal blocks
was questionable, however, the results were inconclusive because there
were several areas where test conditions deviated from the actually
installed conditions. Recently, in order to quantify the performance of
realistically installed and protected terminal blocks in a LOCA
environment, SNL tested 24 more terminal blocks of different models
from four selected manufacturers.
Previous testing data on the terminal blocks indicated that neither the
accelerated aging process nor the seismic testing will significantly
affect terminal block performance; therefore aging and seismic
simulation was not incorporated in the later SNL test. Terminal blocks
were tested in the "as received" condition to simulate normal handling
during installation. Additionally, no special care was taken during
test preparation to prevent the deposit of fingerprints or other
contaminants on the terminal block surfaces.
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Test terminal blocks were installed inside NEMA-4 electrical enclosures
with 1/4" diameter weep holes in the bottom. Cables entered the boxes
from the side through "liquid tight" conduit. To simulate cables
entering through conduit from a cable tray system, the conduit was
terminated inside the test chamber and the conduit end was not sealed.
The test was divided into two phases; each phase was tested under
temperature profiles closely following the PWR temperature profile as
described in Appendix A of IEEE 323-1974.
Phase I consisted of an 11-day exposure to a steam-only environment,
and Phase II consisted of approximately one day of simultaneous
steam/chemical spray followed by a 5-day exposure to a steam
environment. Saturated steam conditions were maintained throughout both
test phases. Details of the test and test connections are being
documented in NUREG/CR-3418 which will soon be published by the NRC.
The terminal blocks were powered at voltages typical of in-plant
applications: 4 V dc typical of RTD circuits, 45 V dc typical of
instrumentation circuits, and 125 V dc typical of control circuits. The
terminal-to-terminal leakage currents were monitored during both Phase
I and Phase II tests, and the terminal-to-ground leakage currents were
monitored during the Phase II tests only.
The SNL test provides the following significant results:
(1) the surface moisture film formed during the test reduced
insulation resistance to 10-2 to 10-5 ohms from initial values of
10-8 to 10-10 ohms; the reduction in insulation resistance
occurred during the steam exposure portion of the LOCA simulation,
(2) at 45 V dc, leakage currents were on the order of 0.1 to 10 mA,
(3) at 4 V dc, insulation resistance was at 5 x 10-3 to 7 x 10-4 ohms,
and
(4) one open failure was observed when leakage currents continued to
increase for a 90-minute period to values which caused a 12-AWG
wire to separate from the terminal point of the terminal block.
The separation occurred at the terminal block - wire junction of a
125 V dc circuit.
2. Low insulation resistance resulted during qualification testing of
terminal blocks used in low voltage instrumentation/control (I/C)
electrical penetration assembly (EPA)
In a Part 50.55(e) Potential Reportable Deficiency Report, the Arizona
Public Service Company (APS) has recently reported to the NRC that
during the review of a qualification test report on terminal blocks
used in low-voltage (I/C) EPA supplied by CONAX Corporation, APS has
observed that insulation resistance (IR) values between terminal points
of the terminal blocks were substantially reduced during simulation of
design basis events. APS concluded that the low-level signals (up to a
maximum 48 V dc and 4-20 mA range) cannot tolerate this low IR
condition. This
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IN 84-47
June 15, 1984
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condition could result in erroneous response in the sensing and control
functions, which in turn might jeopardize reliable plant operation
during accident conditions. APS reported that the test terminal blocks
were made by Kulka Electric Corporation and that during an
investigative test, the terminal blocks also failed the "as-installed
conditions" test in transmitter and RTD circuits. APS further indicated
that Raychem splices are under consideration as replacement for the
terminal blocks for transmitter and RTD circuit applications at the
Palo Verde units.
Discussion:
This information notice highlights a potential concern that may exist when
terminal blocks are exposed to a steam environment.
The results of the SNL test show that a moisture film will form on the
surface of the terminal block during the simulation of the LOCA/MSLB events,
and will result in the reduction of insulation resistance between terminal
points and ground, and thus will allow some leakage currents to flow to
ground.
Based on the review of the SNL test and the review of other qualification
test reports on terminal blocks, the NRC staff recognizes that leakage
currents do exist during LOCA/MSLB simulations and that the leakage currents
may be of significance in some applications. Although no written response to
this notice is required, it is suggested that licensees and construction
permit holders 1) review their facilities to determine if terminal blocks
are used in low-voltage applications, such as in transmitter and RTD
circuits, and 2) review terminal block qualification documents to ensure
that the functional requirements and associated loop accuracy of circuits
utilizing terminal block will not degrade to an unacceptable level due to
the flow of leakage currents that might occur during design basis events.
Instances where fuses were used to monitor leakage currents, and where
failure criteria were based on the failure of these fuses (1 ampere or less)
do not provide information about leakage currents of magnitude that are less
than the fuse rating. Data provided under these instances are not considered
to be acceptable data. The NRC staff considers this review to be part of the
on-going activities that the licensees are currently undertaking to resolve
other environmental qualification deficiencies to meet the deadline and
requirements set forth in the EQ final rule, 10 CFR 50.49.
When supporting data for leakage currents are not substantiated during this
review, one of the following possible corrective actions should be
considered:
1) Perform a valid qualification test of the installed terminal
blocks with provision for the continuous monitoring of leakage
currents throughout the test, and perform analysis to demonstrate
that acceptable loop accuracy and associated response time for
instrument circuit utilizing terminal block are being maintained
throughout various operating conditions.
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2) Obtain documentation from valid qualification tests already
performed with substantiated data for leakage currents, and
perform appropriate analysis as stated in 1) above.
3) Replace the installed terminal blocks with qualified splices.
In addition to the concern of leakage currents being addressed in this
notice, licensees and construction permit holders are reminded that other
information concerning on-going preventive maintenance activities that
involve periodic inspection of terminations and terminal blocks for
cleanliness as described in the previously published information notice No.
82-03 remains in effect.
If you have any questions regarding this matter, please contact the Regional
Administrator of the appropriate NRC Regional office, or this office.
Edward L. Jordan Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: R. G. LaGrange, NRR
(301) 492-8208
N. B. Le, IE
(301) 492-9673
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