Information Notice No. 92-81: Potential Deficiency of Electrical Cables with Bonded Hypalon Jackets

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                     OFFICE OF NUCLEAR REACTOR REGULATION
                            WASHINGTON, D.C.  20555

                               December 11, 1992


NRC INFORMATION NOTICE 92-81:  POTENTIAL DEFICIENCY OF ELECTRICAL CABLES WITH 
                               BONDED HYPALON JACKETS  


Addressees

All holders of operating licenses or construction permits for nuclear power
reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to a potential deficiency in the environmental
qualification of electrical cables with bonded Hypalon jackets.  It is
expected that recipients will review the information for applicability to
their facilities and consider actions, as appropriate.  However, suggestions
contained in this information notice are not NRC requirements; therefore, no
specific action or written response to this notice is required.

Description of Circumstances

Sandia National Laboratories (SNL), under contract to NRC, has been conducting
tests on cables manufactured by three different manufacturers, including
Okonite.  The tests were performed to determine the minimum insulation
thickness necessary for installed cable to perform its intended function
should the insulation be damaged during installation, maintenance, or other
activities.  Therefore, the thermal and radiation aging and loss-of-coolant-
accident (LOCA) testing for the cables were performed with reduced and full
insulation thicknesses.  The Okonite specimens tested were single-conductor,
600-volt, 12 American Wire Gauge (AWG) control cables insulated with ethylene
propylene rubber (EPR) with a bonded Hypalon jacket (Okonite-Okolon).  During
LOCA testing, all 10 of the Okonite-Okolon cable samples failed.  The other
cables in this test program did not have bonded jackets and did not experience
unexpected failures.  

During this test program, the cables were first subjected to 130 megarads of
radiation at the rate of 300 kilorads per hour for 433 hours and were then
thermally aged at 158 �C (316 �F) for 336 hours.  Based on the Arrhenius
equation, accelerated thermal aging at this time and temperature is equivalent
to a 40-year cable life at 69 �C (156 �F) for the jacket and 76 �C (169 �F)
for the insulation.  After thermal aging, through-wall cracks were noted on
most of the Okonite-Okolon cables.  However, the cracks did not prevent the


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cables from passing an insulation resistance (IR) test that was conducted in
a dry environment. 

After the aging and IR tests, the cables were subjected to a LOCA test.  The
test sequence was (1) 94 hours of testing to simulate the LOCA environment
defined in Appendix A to Institute of Electrical and Electronics Engineers
(IEEE) Standard 323-1974, "IEEE Standard for Qualifying Class 1E Equipment for
Nuclear Power Generating Stations," and (2) 146 hours at 121 �C (250 �F) for
the remainder of the test.  No chemical spray was used.  The cables were
energized by 110-volt DC power during the test with no load.  One cable with
full insulation thickness failed just after the test chamber conditions became
saturated at 11-1/2 hours into the test.  By the fifth day of the test, all
the Okonite cables had failed, as indicated by blown 1-ampere fuses.  The test
chamber was opened on October 24, 1992, and the cables were visually
inspected.  The insulation and jacket on the Okonite cables had split down the
length of the cable, and bare conductor was visible.
  
On October 28, 1992, the NRC staff visited SNL to evaluate the test failures. 
During that visit, SNL personnel informed the staff that other Okonite cables
with bonded Hypalon jackets had failed similarly at SNL under another NRC-
sponsored test program (license renewal test program).  For this test, the
cables were thermally aged to the equivalent of a 40-year life at 56 �C
(133 �F).  One out of four Okonite-Okolon cables failed during LOCA testing. 
Another group of Okonite cables that had been aged to a 40-year life at 50 �C
(122 �F) passed this testing.

In addition to the Okonite failures in the license renewal test program,
cables manufactured by Samuel Moore also failed during LOCA testing.  These
cables were Dekoron Dekorad Type 1952, two-conductor, twisted, shielded pair,
16 AWG instrument cables covered with ethylene-propylene diene monomer (a type
of EPR) insulation with a bonded Hypalon jacket and an overall jacket of
Hypalon.  One cable in which one conductor failed had been thermally aged to
a 20-year life at 55 �C (131 �F), while the other cable in which both
conductors failed had been thermally aged to a 40-year life at 56 �C (133 �F). 
These failures were similar to the failure of the Okonite-Okolon cable in that
the insulation and bonded jacket had split open.  Other samples of Samuel
Moore cable survived aging and accident testing under similar conditions.

Discussion

The SNL test results from NRC-sponsored programs raise questions with respect
to the environmental qualification of Okonite cables with bonded Hypalon
jackets that have not been specifically qualified for service conditions
exceeding 50 �C (122 �F) for 40 years.  The staff reviewed the qualification
data developed by the Okonite Company and noted that Okonite 2 kV cables with
0.76 mm [30 mil] bonded Hypalon jackets and 600-volt cables with unjacketed
EPR insulation were previously tested.  The 600-volt cables with 0.38 mm [15
mil] bonded Hypalon jackets were qualified based on the previous 2 kV and 600-
volt test results.  It was believed that if the unjacketed EPR insulation
passed qualification testing, then EPR insulation with a bonded jacket would.

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also pass qualification testing.  However, the Sandia test results indicate
that Okonite cable with bonded Hypalon jackets may be susceptible to failure.

The qualification data reviewed by the staff for the Samuel Moore cables
showed that cables with bonded Hypalon jackets had been previously tested by
Isomedix, Inc.  The tests documented qualification of the Dekoron Dekorad
cable to a qualified life of 40 years at plant service conditions of 52 �C
(126 �F) or less.  The test results from the license renewal test program at
SNL raise questions about the qualification of Samuel Moore Dekoron Dekorad
Type 1952 cables when used at higher temperatures.

Other bonded-jacket cables, qualified for up to 90 �C (194 �F) applications as
claimed by various vendors, may be susceptible to the same type of failures if
not specifically tested in the bonded confirguration.  The difference in aging
rates between the jacket and the insulation may be a factor in the failure of
bonded-jacket cables.  Therefore, qualification testing that does not use the
jacketed configuration may not be representative of actual cable performance. 

Depending on the application, failure of these cables could affect the
performance of safety functions in nuclear power plants.  The functional
integrity of the cables could be affected if the cables are used inside
containment, used in continuous power circuits, routed with power cables, or 
routed close to hot pipes.  Generic Letter 88-07, "Modified Enforcement Policy
Relating to 10 CFR 50.49, `Environmental Qualification of Electrical Equipment
Important to Safety for Nuclear Power Plants,'" provides relevant information
on dealing with potential environmental qualification deficiencies.  

This information notice requires no specific action or written response.  If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.


                                       ORIGINAL SIGNED BY


                                    Brian K. Grimes, Director
                                    Division of Operating Reactor Support
                                    Office of Nuclear Reactor Regulation

Technical contacts:  Hukam C. Garg, NRR
                     (301) 504-2929
   
                     Ann M. Dummer, NRR
                     (301) 504-2831

Attachment:  List of Recently Issued NRC Information Notices
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