United States Nuclear Regulatory Commission - Protecting People and the Environment

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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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
Page Last Reviewed/Updated Tuesday, November 12, 2013