Information Notice No. 91-79: Deficiencies Found in Thermo-Lag Fire Barrier Installation
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
December 6, 1991
NRC INFORMATION NOTICE 91-79: DEFICIENCIES IN THE PROCEDURES FOR INSTALLING
THERMO-LAG FIRE BARRIER MATERIALS
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 problems that could result from improperly
installed THERMO-LAG 330-1 fire barriers that are used to satisfy NRC fire
protection requirements for safe shutdown components. 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 new NRC
requirements; therefore, no specific action or written response is required.
Description of Circumstances
NRC Information Notice (IN) 91-47, "Failure of THERMO-LAG Fire Barrier
Material to Pass Fire Endurance Test," reported a number of installation
deficiencies identified at the River Bend Station (RBS) and discussed a ASTM
E-119 fire endurance test conducted for Gulf States Utilities (GSU) in
October 1989 at Southwest Research Institute (SwRI) that ended with a
failure of a 3-hour THERMO-LAG 330-1 cable tray protective envelope system.
On August 23, 1991, the vendor, Thermal Science, Incorporated, (TSI), issued
a letter to a number of licensees that discussed specific installation
issues raised in IN 91-47 and concluded that the SwRI fire endurance test
was not a valid test because of deficiencies in the installation of the test
Other licensees have also identified instances of THERMO-LAG fire barrier
configurations that were not installed in accordance with the vendor's
installation procedures manual. For example, Cleveland Electric
Illuminating Company (CEI) reported in Licensee Event Report 91-020 that the
mechanical fasteners (banding straps) on the fire barrier enclosures at
Perry Nuclear Power Plant had not been installed in accordance with the
vendor's installation procedures manual. CEI identified the installation
discrepancies while conducting routine fire wrap inspections using revised
inspection criteria. The licensee
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identified that no fire endurance tests or engineering analysis had been
performed to support the installed configuration. The licensees that have
experienced installation problems have attributed most of the reported
installation problems to contractor installer errors, incomplete or
incorrect design documents, and inadequate quality control oversight. The
NRC has also identified a number of installation variations as it has
continued to review the vendor's installation procedures and the
installation specifications, procedures, and practices for specific plants.
Some of the installation variations observed by the NRC do not appear to be
in accordance with the vendor's installation procedures manual and may
comprise configurations that have not been qualified by fire endurance
testing or engineering analyses. In several cases, such as at the River
Bend Station (RBS) and Washington Nuclear Power Unit 2 (WNP2), the
installation methods used during initial construction of the plant that
deviated from the vendor's installation procedures manual were found
unacceptable when subsequent qualification fire endurance testing resulted
in fire barrier failures.
On October 17, 1991, the NRC met with TSI to discuss issues regarding
installation and qualification testing. The vendor stated that it had not
included several essential application steps and precautions in its
installation procedures manual because the information was presented during
the TSI certification training for installers. The vendor stressed the
importance of using skilled and certified craftsmen, and qualified quality
control inspectors to achieve an adequate fire barrier enclosure. In
addition, several licensees have related to the NRC receiving supplementary
written and verbal installation guidance from TSI representatives that is
not included in the TSI installation procedures manual.
The NRC has discussed installation details with licensees, and visited a
number of sites. The staff has observed variations among the installation
procedures and practices regarding the following fabrication details:
- Methods for sealing and filling joints between panel sections.
- The orientation and application methods for stress skin.
- The requirements for raceway support protection.
- Allowable gap widths between panel sections.
- The configuration and orientation of structural ribs.
- Methods for installing vaults and firewalls.
- Banding material and application methods.
- Scoring and grooving of panels for fabricating and bending the
panels around bends in raceways.
- Thickness acceptance criteria.
For example, an important task during the installation of THERMO-LAG fire
barriers is the filling of the joints between adjoining prefabricated panel
sections with trowel-grade material to the full depth of the panels. Some
facilities use a method in which the ends of individual panel sections are
butt joined to one another and the seam between the panel sections is filled
and covered with THERMO-LAG trowel grade material (commonly referred to as
"dry-fitting"). Some licensees fill the joints by "pre-buttering" the edges
of the individual panel sections with trowel grade material before they join
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panels to ensure that the gap between the panels is completely filled. The
vendor did not list this method as an option for installing cable tray
enclosures in its current installation procedures manual. However, on
October 17, 1991, the vendor stated to the NRC that this method was
acceptable for installing THERMO-LAG panels to cable trays. In its
August 23, 1991, letter to licensees, the vendor stated that stress skin
must be placed over panel joints to ensure a continuous outer layer of
stress skin for 3-hour barriers and a recent vendor procedure, TSI Technical
Note 20684-AL, of October 1989, provides updated installation procedures for
aluminum cable trays and requires that each butt joint be covered by an
additional layer of stress skin and trowel grade material. The current
vendor's generic installation procedures manual does not provide any
guidance for installing a continuous layer of stress skin.
The NRC has not been able to verify that all of the specific installation
variations observed have been qualified by independent qualification testing
or engineering analyses. The NRC is continuing to review other technical
issues regarding THERMO-LAG 330-1 fire barriers, including issues concerning
the adequacy of qualification testing. Generic Letter 86-10,
"Implementation of Fire Protection Requirements," provides additional NRC
guidance on fire barrier qualification test acceptance criteria and
evaluation of deviations from tested configurations to substantiate field
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.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contacts: Ralph Architzel, NRR
Loren R. Plisco, NRR
K. Steven West, NRR
Attachment: List of Recently Issued NRC Information Notices
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