Bulletin 92-01: Failure of Thermo-Lag 330 Fire Barrier System to Maintain Cabling in Wide Cable Trays and Small Conduits Free from Fire Damage
OMB No.: 3150-0012
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
June 24, 1992
NRC BULLETIN NO. 92-01: FAILURE OF THERMO-LAG 330 FIRE BARRIER SYSTEM TO
MAINTAIN CABLING IN WIDE CABLE TRAYS AND SMALL
CONDUITS FREE FROM FIRE DAMAGE
All holders of operating licenses for nuclear power reactors.
All holders of construction permits for nuclear power reactors.
This bulletin notifies you of failures in fire endurance testing associated
with the Thermo-Lag 330 fire barrier system that is installed to protect safe
shutdown capability, requests all operating reactor licensees to take the
recommended actions, and requires that these licensees provide the U.S.
Nuclear Regulatory Commission (NRC) with a written response describing the
actions taken associated with this bulletin.
On August 6, 1991, the NRC issued Information Notice (IN) 91-47, "Failure of
Thermo-Lag Fire Barrier Material To Pass Fire Endurance Test," which provided
information on the fire endurance tests performed by the Gulf States
Utilities Company on Thermo-Lag 330 fire barrier systems installed on wide
aluminum cable trays and the associated failures. On December 6, 1991, the
NRC issued Information Notice 91-79, "Deficiencies In The Procedures For
Installing Thermo-Lag Fire Barrier Material," which provided information on
deficiencies in procedures that the vendor (Thermal Science, Inc.) provided
for installing Thermo-Lag 330 fire barrier material. As a result of on-
going concerns associated with the indeterminate qualifications of Thermo-
Lag 330 fire barrier installations, on June 23, 1992, the NRC issued
Information Notice 92-46, "Thermo-Lag Fire Barrier Material Special Review
Team Final Report Findings, Current Fire Endurance Testing, and Ampacity
Description of Circumstances
Upon reviewing INs 91-47 and 91-79, Texas Utilities (TU) Electric instituted
a fire endurance testing program to qualify its Thermo-Lag 330 electrical
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raceway fire barrier systems for its Comanche Peak Steam Electric Station.
The testing was performed during the weeks of June 15 and June 22, 1992.
TU Electric's test program consisted of a series of 1-hour fire endurance
tests (using the ASTM-E119 Standard Time Temperature Curve) on a variety of
cable tray and conduit "mock-ups." TU Electric designed these "mock-ups" or
test articles to duplicate existing installed plant configurations. Plant
personnel used stock material to construct the test articles. The Thermo-
Lag fire barrier installation on the test articles was performed in
accordance with TU Electric's Thermo-Lag installation procedures. These
procedures were developed from the vendor's recommended installation
The Thermo-Lag fire barrier systems for the TU Electric test articles were
constructed using pre-formed 1-hour Thermo-Lag 330 panels and conduit shapes.
The joints and seams were constructed by pre-buttering seams and joints with
trowel grade Thermo-Lag 330-1 and holding the assembly together with
stainless steel banding.
On June 17, 1992, the first test article was tested. This article consisted
of a junction box with a 3/4-, 1-, and 5-inch conduit entering and exiting
through the junction box. Throughout the 1-hour fire endurance test, the
cabling routed inside the conduits was monitored in accordance with the
American Nuclear Insurer's criteria for low voltage circuit integrity and
continuity. Throughout the test, none of the cables experienced a failure
in circuit integrity. The licensee noted that the thermocouple temperature
on the inside cover of the junction box on the unexposed side reached 539 �F
and that hot spots (temperatures on the cable in excess of 500 �F) on the
3/4-inch conduit and the 1-inch conduit developed. On June 18, 1992, the
cables were pulled from the test article. There were no visible signs of
thermal degradation on the cables routed in the 5-inch conduit. The cable
inside the 3/4-inch conduit was thermally damaged in two locations and cable
in the 1-inch conduit was damaged in one location.
On June 18, 1992, TU Electric performed a 1-hour fire endurance test on a 12-
inch wide tray configuration. Preliminary test result information indicated
that the configuration passed the test satisfactorily. Throughout the fire
endurance test, the thermocouple temperatures on the cables inside the test
article were less than 325 �F.
On June 19, 1992, a 30-inch wide ladder back tray configuration was tested.
At 17 minutes into the test, the Thermo-Lag 330 panel on the bottom of the
test article began to sag. At 18 minutes, the joint at the interface between
the tray support and the tray showed signs of weakening and separation. The
internal temperatures within areas of the test article showed signs of
exceeding 325 �F at 25 minutes. The joint fully separated in 41 minutes
resulting in cable circuit integrity failure and fire damage to the cables.
Section 50.48(a) of Title 10 of the Code of Federal Regulations
(10 CFR 50.48(a)) requires that each operating nuclear power plant have a
June 24, 1992
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protection plan that satisfies Appendix A to 10 CFR Part 50, General Design
Criteria (GDC) 3, "Fire Protection." GDC 3 requires structures, systems, and
components important to safety be designed and located to minimize, in a
manner consistent with other safety requirements, the probability and effects
of fires and explosions. In 10 CFR 50.48(b), the NRC states that Appendix R
to 10 CFR Part 50 establishes fire protection features required to satisfy
Criterion 3 of Appendix A to 10 CFR Part 50 for certain generic issues for
nuclear power plants licensed to operate prior to January 1, 1979.
Sections III.G, III.J, and III.0 of Appendix R are applicable to nuclear
power plants licensed to operate prior to January 1, 1979. In 10 CFR
50.48(e), the NRC requires that all plants licensed to operate after January
1, 1979, shall complete all fire protection modifications needed to satisfy
Criterion 3 to Appendix A of 10 CFR Part 50 in accordance with the provisions
of their operating licenses.
NRC-approved plant fire protection programs as referenced by the Plant
Operating License Conditions and Appendix R to 10 CFR Part 50, Section
III G.1.a, "Fire Protection of Safe Shutdown Capability," require one train
of systems necessary to achieve and maintain hot shutdown conditions from
either the control room or emergency control stations to be free from fire
To ensure that electrical cabling and components are free from fire damage,
Section III G.2 of Appendix R requires the separation of safe shutdown trains
by separation of cables and equipment and associated circuits of redundant
trains by a fire barrier having a 3-hour rating or enclosure of cable and
equipment and associated non-safety circuits of one redundant train in a fire
barrier having a 1-hour rating. In addition to providing the 1-hour barrier,
fire detection and an automatic fire suppression system shall be installed
in the fire area.
Under fire conditions, the thermal degradation of an electrical raceway fire
barrier system, such as the Thermo-Lag system, could lead to both trains of
safe shutdown systems being damaged by fire. This may significantly affect
the plant's ability to achieve and maintain hot standby/shutdown conditions.
The NRC considered the failures of the recent Thermo-Lag fire barrier fire
endurance testing and has determined that the 1- and 3-hour pre-formed
assemblies installed on small conduit and wide cable trays (wider than
14 inches) do not provide the level of safety as required by NRC
All holders of operating licenses for nuclear power reactors, immediately
upon receiving this bulletin, are requested to take the following actions:
1. For those plants that use either 1- or 3-hour pre-formed Thermo-Lag 330
panels and conduit shapes, identify the areas of the plant which have
Thermo-Lag 330 fire barrier material installed and determine the plant
areas which use this material for protecting either small diameter
conduit or wide trays (widths greater that 14 inches) that provide safe
June 24, 1992
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2. In those plant areas in which Thermo-Lag fire barriers are used to
protect wide cable trays, small conduits, or both, the licensee should
implement, in accordance with plant procedures, the appropriate
compensatory measures, such as fire watches, consistent with those
which would be implemented by either the plant technical specifications
or the operating license for an inoperable fire barrier.
3. Each licensee, within 30 days of receiving this bulletin, is required
to provide a written notification stating whether it has or does not
have Thermo-Lag 330 fire barrier systems installed in its facilities.
Each licensee who has installed Thermo-Lag 330 fire barriers is
required to inform the NRC, in writing, whether it has taken the above
actions and is required to describe the measures being taken to ensure
or restore fire barrier operability.
These types of fire barriers are currently installed at operating power
reactor sites and are required to meet either a condition of a plant's
operating license or the requirements of Section III.G of Appendix R to
10 CFR Part 50. The actions requested by this bulletin do not represent a
new staff position but are considered necessary to bring licensees into
compliance with existing NRC rules and regulations where these test results
are relevant. Therefore, this bulletin is being issued as a compliance
backfit under the terms of 50.109(a)(4). In addition, pursuant to the
Charter of the Committee to Review Generic Requirements (CRGR), this bulletin
is being issued as an immediately effective action (10 CFR 50.109(a)(6)).
This bulletin is being issued with the knowledge of the CRGR.
Address the required written reports to the U. S. Nuclear Regulatory
Commission, ATTN: Document Control Desk, Washington, D.C. 20555, under oath
or affirmation under the provisions of Section 182a, Atomic Energy Act of
1954, as amended and 10 CFR 50.54(f). In addition, submit a copy to the
appropriate regional administrator.
This request is covered by Office of Management and Budget Clearance Number
3150-0012, which expires June 30, 1994. The estimated average number of
burden hours is 60 person hours for each licensee response, including those
needed to assess the new recommendations, search data sources, gather and
analyze the data, and prepare the required letters. This estimate of the
average number of burden hours pertains only to the identified response-
related matters and does not include the time needed to implement the
requested action. Send comments regarding this burden estimate or any other
aspect of this collection of information, including suggestions for reducing
this burden, to the Information and Records Management Branch, Division of
Information Support Services, Office of Information Resources Management, U.
S. Nuclear Regulatory Commission, Washington, D.C. 20555, and to the
Paperwork Reduction Project (3150-0011), Office of Information and Regulatory
Affairs, NEOB-3019, Office of Management and Budget, Washington, D.C. 20503.
June 24, 1992
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Although no specific response is required with respect to the following
information, the following information would assist the NRC in evaluating the
cost of complying with this bulletin:
(1) the licensee staff's time and costs to perform requested inspections,
corrective actions, and associated testing;
(2) the licensee staff's time and costs to prepare the requested reports
(3) the additional short-term costs incurred to address the inspection
findings such as the costs of the corrective actions or the costs of
down time; and
(4) an estimate of the additional long-term costs that will be incurred as
a result of implementing commitments such as the estimated costs of
conducting future inspections or increased maintenance.
If you should have any questions about this matter, please contact one of the
technical contacts listed below or the appropriate NRR project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contacts: Ralph Architzel, NRR
Patrick Madden, NRR
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