United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 91-47: Failure of THERMO-LAG Fire Barrier Material to pass Fire Endurance Test

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

                               August 6, 1991


Information Notice No. 91-47:  FAILURE OF THERMO-LAG FIRE BARRIER 
                                   MATERIAL TO PASS FIRE ENDURANCE TEST


Addressees:

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

Purpose:

This information notice is intended to alert addressees to problems that 
could result from the use of or improper installation of THERMO-LAG material 
to satisfy the electrical raceway fire protection requirements for safe 
shutdown components specified in Section III.G.2 of Appendix R to Part 50 of 
Title 10 of the Code of Federal Regulations (10 CFR Part 50).  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 do not 
constitute any new Nuclear Regulatory Commission (NRC) requirements; 
therefore, no specific action or written response is required.

Description of Circumstances:

The Gulf States Utilities Company, the licensee for the River Bend Station 
(RBS), submitted Licensee Event Reports (LERs) 87-005, 89-009, 90-003, and 
an Informational Report to the NRC concerning deficiencies identified in 
fire barriers.  The NRC staff reviewed test report information and 
associated documents regarding the RBS electrical raceway fire barriers to 
determine if the problems identified in the LERs and Informational Report 
could affect other NRC licensees.  The electrical raceway fire barrier 
material used at RBS is THERMO-LAG, a product manufactured and supplied by 
Thermal Science, Incorporated, (TSI), of St. Louis, Missouri.  TSI provides 
THERMO-LAG for 1-hour and 3-hour rated fire barriers.

A 3-hour fire endurance test of a 30-inch aluminum electrical cable tray was 
performed in October 1989 at the Southwest Research Institute (SwRI) for 
Gulf States Utilities Company.  In this test, a THERMO-LAG envelope system 
failed resulting in high temperatures inside the cable tray envelope and 
loss of circuit integrity within approximately 60 minutes.  Catastrophic 
failure and collapse of the tray occurred within 1 1/2 hours.  The failure 
of this test raised concerns regarding the adequacy of THERMO-LAG cable tray 
enclosures protecting 30-inch wide cable trays.


9108020180 
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Discussion:

NRC requirements and guidelines for fire barriers are contained in various 
documents, including Appendix R to 10 CFR 50, Generic Letter 86-10, 
"Implementation of Fire Protection Requirements", and NUREG-0800, "Standard 
Review Plan."  The extent to which these requirements or guidelines are 
applicable to a specific plant depends on plant age, commitments established 
by the licensee in developing the fire protection plan, the staff safety 
evaluation reports (SERs) and supplements, and the license conditions 
pertaining to fire protection.  Fire barrier wrap material is designed to 
provide reasonable assurance that the effects of a fire are limited to one 
division of a safe shutdown related system while another division will 
remain free of fire damage.

The Gulf States Utilities Company uses THERMO-LAG to protect raceways and 
components throughout RBS that are related to safe shutdown.  In addition, 
at least 40 NRC licensed facilities use THERMO-LAG to construct fire barrier 
assemblies with 3-hour and 1-hour ratings to enclose electrical raceway and 
other safe shutdown components.

During routine walkdown inspections in early 1987, RBS fire protection 
personnel identified degradation of the THERMO-LAG 1-hour and 3-hour rated 
barriers.   During repairs to correct the deficiencies discovered during the 
walkdowns, the licensee found that the fire barriers had not been installed 
in accordance with the manufacturer's specifications.  The large number of 
observed deficiencies prompted the licensee to expand these walkdown 
inspections to include all THERMO-LAG fire barriers.  Hourly fire watches 
were posted in all affected safety-related areas pending completion of all 
inspections and correction of any deficiencies found.  The licensee 
attributed the deficiencies to failure of the subcontractor installation and 
quality control inspection program.

During maintenance activities in early 1989, the licensee found additional 
deficiencies indicating an apparent deficiency in the installation and 
quality control inspection program.  The subcontractor who installed the 
THERMO-LAG fire barriers at RBS was approved by TSI as a qualified 
installer.  However, during the installation at RBS, the subcontractor 
removed the factory-installed components of the THERMO-LAG called "stress 
skin" and structural ribbing.  The stress skin component, a wire mesh, is 
critical to the structural integrity of the fire product during fire 
exposure.  The RBS fire protection personnel considered that all barriers 
were degraded because of the many sections of the inside layer of the stress 
skin that had been removed during initial installation at RBS.  

The discrepancies identified between the manufacturer's installation manual, 
actual site installation manual and qualification fire tests resulted in the 
licensee conducting additional fire endurance testing.  In October 1989, 
SwRI tested a U-shaped 30-inch wide aluminum ladder back cable tray enclosed 
in a 3-hour fire-rated barrier constructed of THERMO-LAG material.  RBS 
personnel constructed the cable tray protective envelope in accordance with 
the manufacturer's published installation instructions.
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During the 3-hour fire endurance test, all thermocouples inside the 
THERMO-LAG protected tray reached failure temperatures (>325�F) in times 
ranging from approximately 45 minutes to 80 minutes.  Conductor-to-ground 
failure occurred in the power cable at 60 minutes.  The THERMO-LAG enclosure 
disintegrated at 77 minutes, and the cable tray collapsed at 82 minutes.  
The SwRI test results on the as-designed THERMO-LAG configuration prompted 
RBS to institute a fire watch patrol in all areas that depend on THERMO-LAG 
barriers for protection of safe shutdown capability.  

Additional deficiencies, such as small holes, cracks and unfilled seams, 
were found in the THERMO-LAG material during walkdowns conducted in early 
1990.  The licensee conducted additional testing of as-installed barriers in 
November and December 1990.  Certain 1-hour and 3-hour cable tray and 
conduit envelope tests failed.  The envelopes were upgraded and tests of the 
upgraded barriers passed with the exception of the 3-hour cable tray 
envelope.  Final resolution of the 3-hour envelope may include replacing 
existing fire wrap materials with fully qualified fire wrap, repairing and 
then qualifying in-plant fire wrap assemblies by supplemental fire tests, or 
rerouting the cables into acceptable enclosures.

Additionally, other fire barrier wrap design and installation concerns have 
been reported by RBS that indicate the possibility that NRC requirements for 
fire protection were not being met in all aspects.  The type of concerns 
identified to date include the following:

1.   Lack of documentation of qualification tests which demonstrate that 
     aluminum conduits penetrating the THERMO-LAG protective envelope have 
     been tested.

2.   Lack of documentation of qualification tests for different joint 
     installations that demonstrate that varying fitup methods (i.e., dry 
     fitting) are qualified.

3.   Lack of documentation of qualification tests of THERMO-LAG 
     installations applicable to large cable trays.  The licensee questioned 
     the validity of extrapolating results from small cable tray tests to 
     its 30-inch wide trays. 

The NRC is particularly interested in obtaining information on fire barriers 
that have been found with deficiencies similar to those described in this 
notice.  Documentation, in as much detail as practicable, of any such 
deficiencies discovered, especially in cases where a fire barrier may have 
been improperly installed or tested is important.  Licensees may communicate 
the availability of information of this type by telephone to the NRC 
technical contact listed below.  Information Notice No. 88-04, "Inadequate 
Qualification and Documentation of Fire Barrier Penetration Seals," provides 
additional discussion and considerations regarding qualification of 
installed fire barriers.

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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.




                                   Charles E. Rossi, Director
                                   Division of Operational Events Assessment
                                   Office of Nuclear Reactor Regulation


Technical Contact:  Ralph Architzel, NRR
                    301-492-0804


Attachment:  List of Recently Issued NRC Information Notices
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