Information Notice No. 87-52:Insulation Breakdown of Silicone Rubber-Insulated Single Conductor Cables During High Potential Testin
SSINS No.: 6835
IN 87-52
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
October 16, 1987
Information Notice No. 87-52: INSULATION BREAKDOWN OF SILICONE
RUBBER-INSULATED SINGLE CONDUCTOR
CABLES DURING HIGH POTENTIAL TESTING
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice is being provided to alert addressees to potential
problems resulting from insulation breakdown of various silicone rubber-
insulated single conductor cables discovered during special high-potential
tests. It is expected that recipients will review the information for appli-
cability to their facilities and consider actions, as appropriate, to avoid
similar problems. However, suggestions contained in this information notice
do not constitute NRC requirements; therefore, no specific action or written
response is required.
Description of Circumstances:
On September 4, 1987, the Tennessee Valley Authority (TVA) notified the
Nuclear Regulatory Commission (NRC), pursuant to the requirements of 10 CFR
Part 21, of several failures of silicone rubber-insulated cables during high
potential testing. The insulation failures occurred on three different
silicone rubber-insulated single conductor No. 14 cables manufactured by the
American Insulated Wire (AIW) Corporation and installed at TVA's Sequoyah
Nuclear Plant. Subsequent testing by TVA found three additional insulation
failures in silicone rubber-insulated cables manufactured by AIW and three
failures in cables manufactured by the Rockbestos Company. To date, the
licensee has found a total of 9 failures out of 91 tested conductors; however,
the licensee has not determined the cause of these failures. TVA has
concluded that the performance of the silicone rubber-insulated cables is
significantly different from other cables at TVA facilities, where 923 tests
were recently completed with no failures.
Discussion:
Additional laboratory testing of the silicone rubber-insulated cables, author-
ized by TVA, indicated that significant decreases in insulation wall thickness
could result from lower-than-expected impact forces. The licensee speculates
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October 16, 1987
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that such impact forces, which could affect the dielectric withstand charac-
teristics of the cable, may occur during (1) handling by the manufacturer,
(2) shipping, (3) receipt and storage by TVA, or (4) the installation process.
A failure of the cable at voltages below those accepted by the industry to
demonstrate insulation integrity during equipment qualification testing may
indicate the inability of the cable to perform its intended function under
design basis accident conditions. For this reason, the licensee and the NRC
are continuing to evaluate the silicone rubber-insulated cable failures. TVA
is planning to perform additional high-voltage withstand tests on an expanded
sample of the installed cables to provide a level of confidence in the integ-
rity of the cable commensurate with that provided during the equipment
qualification testing previously performed.
The results of the additional testing planned by TVA, as well as the results
of those tests previously performed on installed cables, will be analyzed by
TVA and the NRC to determine the extent of the problem.
The NRC will take appropriate regulatory action, such as issue a bulletin, if
it is determined that the inability of these cables to perform as designed
could create a substantial safety hazard.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical
contact listed below or the Regional Administrator of the appropriate regional
office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: Jim Knight, NRR
(301) 492-7456
Angelo Marinos, OSP
(301) 492-9041
Jaime Guillen, NRR
(301) 492-8933
Attachment: List of Recently Issued NRC Information Notices
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