United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 94-34: Thermo-Lag 330-660 Flexi-Blanket Ampacity Derating Concerns

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                            WASHINGTON, D.C.  20555

                                 May 13, 1994

                               DERATING CONCERNS


All holders of operating licenses or construction permits for nuclear power


The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to a potential problem involving the use of
nonconservative ampacity derating data by licensees based on previous
representations by the vendor, Thermal Science, Inc. (TSI).  It is expected
that recipients will review the information for applicability to their
facilities and consider actions, as appropriate, to avoid similar problems. 
However, suggestions contained in this information notice are not NRC
requirements; therefore, no specific action or written response is required.

Description of Circumstances

The vendor, TSI, stated in a purchase document, "TSI's Bid Document 618,"
dated June 25, 1986, for Northeast Utilities Service Company (Millstone 
Units 1 and 2) that the Thermo-Lag 330-660 Flex-Blanket material will produce
test results similar to those of the Thermo-Lag 330-1 material.  For example,
the vendor cited a 7.47 percent ampacity derating factor for the Thermo-
Lag 330-1 material based on reported test results for a 1-hour-rated fire
barrier conduit system.

On November 8, 1993, the NRC staff wrote to TSI requesting information
regarding the ampacity derating data provided licensees for the application of
the Thermo-Lag 330-660 Flexi-Blanket fire barrier system.

On December 22, 1993, TSI responded stating that Texas Utilities Electric
Company had recently conducted an ampacity derating test at the Omega Point
Test Laboratories.  The test, using a 1-hour design (three 0.64 cm  
[0.250 inch] layers) of the Thermo-Lag 330-660 Flexi-Blanket material, had
resulted in a 21.2 percent ampacity derating factor for a 3C/#6 AWG Air Drop
configuration.  In addition, the vendor stated that, to the best of its
knowledge, no ampacity derating test has been performed on the 3-hour design
(five 0.64 cm [0.250 inch] layers) of the Thermo-Lag 330-660 Flexi-Blanket
fire barrier system.

9405090108.                                                            IN 94-34
                                                            May 13, 1994
                                                            Page 2 of 3

Attachment 1 contains a list of the organizations that TSI identified as
having purchased the Thermo-Lag 330-660 Flexi-Blanket material for use in
nuclear power generating plants.


Title 10 of the Code of Federal Regulations, Part 50, Appendix A, General
Design Criterion (GDC) 17, "Electric power systems," if applicable, requires
that onsite and offsite electric power systems be provided to permit the
functioning of structures, systems, and components important to safety.  The
safety function of either electrical power system (assuming the other system
is not functioning) is to provide sufficient capacity and capability to ensure
that vital functions are maintained.  Cables routed in electrical raceways are
derated to ensure that systems have sufficient capacity and capability to
perform their intended safety functions.  Other factors that affect ampacity
derating include cable fill, cable loading, cable type, raceway construction,
and ambient temperature.

Cable derating calculations that are based on inaccurate or nonconservative
derating factors could result in the installation of undersized cables or
overfilling of raceways.  Either of these conditions could cause operating
temperatures to exceed design limits within the raceways, thereby reducing the
expected design life of the cables.  TSI stated in the 1986 procurement
document referenced above that the Thermo-Lag 330-660 material will produce
similar ampacity results as those of the Thermo-Lag 330-1 material.  Because
of the wide range of ampacity derating factors documented for various Thermo-
Lag materials, some licensees may not have adequately accounted for the
insulating effects of the Thermo-Lag 330-660 material in their derating

The National Electrical Code, Insulated Cable Engineers Association
publications, and other industry standards provide general ampacity derating
factors for open-air installations, but do not include derating factors for
fire barrier systems.  The Insulated Conductors Committee of the Institute of
Electrical and Electronics Engineers (IEEE) Power Engineering Society, Task
Force 12-45, has been developing IEEE Standard Procedure P848, "Procedure for
the Determination of the Ampacity Derating of Fire Protected Cables," for use
as an industry standard.  The industry consensus standard development process
may result in the formulation of a uniform technical approach to the deter-
mination of ampacity derating factors for cables enclosed by fire barrier

Related Generic Communications

In NRC Information Notice (IN) 92-46, "Thermo-Lag Fire Barrier Material
Special Review Team Final Report Findings, Current Fire Endurance Tests, and
Ampacity Calculation Errors," the staff informed licensees that a licensee had
discovered a mathematical error in the calculation of the ampacity derating .                                                            IN 94-34          
                                                            May 13, 1994
                                                            Page 3 of 3

factor as published in an Industrial Testing Laboratories, Incorporated, test
report.  A preliminary assessment of the use of lower-than-actual ampacity
derating factors indicates that the Thermo-Lag barrier installations may allow
cables to reach temperatures that exceed their ratings, which could accelerate
cable aging.

In IN 94-22, "Fire Endurance and Ampacity Derating Test Results for 3-Hour
Fire-Rated Thermo-Lag 330-1 Fire Barriers," the staff informed licensees of  
the preliminary results of fire endurance and ampacity derating tests
conducted by NRC at the Underwriters Laboratories, Incorporated, during
December 1993.  The principal objective of the tests was to evaluate the
performance of the barriers against the results of tests previously reported
by TSI.

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

                                    /S/'D BY BKGRIMES

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

Technical contact:  Ronaldo V. Jenkins, NRR
                    (301) 504-2985

1.  Licensees Who Purchased Thermo-Lag 330-660 
      Flexi-Blanket Thermal Barrier Material
2.  List of Recently Issued NRC Information Notices

.                                                            Attachment No. 1
                                                            IN 94-34
                                                            May 13, 1994
                                                            Page 1 of 1

                            LICENSEES WHO PURCHASED

Utility.Facility.Carolina Power & Light Co..Brunswick.Cleveland Electric Illuminating Co..Perry Nuclear Plant.Commonwealth Edison.Braidwood Station.Entergy Operations, Inc..Waterford 3.Consumers Power.Palisades.Florida Power Corporation.Crystal River Unit 3.Fluor Engineers Co..San Onofre.Georgia Power.E. I. Hatch..Plant Vogtle.Gulf States Utilities.River Bend.GPU Nuclear.Oyster Creek..Three Mile Island.Long Island Lighting.Shoreham.Iowa Electric.Duane Arnold Plant.Northern States Power.Prairie Island.South Carolina Electric & Gas Co..Virgil C. Summer.Tennessee Valley Authority.Browns Ferry..Watts Bar.Toledo Edison Co..Davis Besse Power Station.Texas Utilities Electric.Comanche Peak Units 1 and 2.Washington Public Power Supply System.WNP-2
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