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United States Nuclear Regulatory Commission - Protecting People and the Environment

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                                                           OMB No.:  3150-0012
                                                           NRCB 92-01, SUPP. 1

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

                                August 28, 1992


NRC BULLETIN NO. 92-01, SUPPLEMENT 1:  FAILURE OF THERMO-LAG 330 FIRE BARRIER
                                       SYSTEM TO PERFORM ITS SPECIFIED FIRE
                                       ENDURANCE FUNCTION

Addressees 

For Action:

All holders of operating licenses for nuclear power reactors

For Information:

All holders of construction permits for nuclear power reactors


Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this bulletin
supplement to notify licensees and construction permit holders of additional
apparent failures in fire endurance testing associated with the Thermo-Lag 330
fire barrier system which many plants have installed to protect safe shutdown
capability, to request all operating reactor licensees that have Thermo-Lag
fire barriers to take the recommended actions, and to require that these
licensees submit a written response to the NRC describing the actions taken
associated with this bulletin supplement. 

Background

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 contained
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
IN 91-79, "Deficiencies In The Procedures For Installing Thermo-Lag Fire
Barrier Materials," which contained information on deficiencies in procedures
that the vendor (Thermal Science, Inc.) supplied for installing Thermo-Lag 330
fire barrier material.  Recognizing the concerns stated in INs 91-47 and 91-79
regarding the Thermo-Lag 330 fire barrier system, Texas Utilities (TU)
Electric instituted a fire endurance testing program to qualify its Thermo-Lag
330 electrical raceway fire barrier systems for its Comanche Peak Steam
Electric Station.  On June 17-23, 1992, TU Electric conducted the first series
of these "full scale" fire endurance tests at Omega Point Laboratories in San
Antonio, Texas. 


9208280400.

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The results of these tests have raised questions regarding the ability of the
Thermo-Lag 330 fire barrier system to perform its specified function as a 
1-hour fire barrier.  On June 23, 1992, the NRC issued IN 92-46, "Thermo-Lag
Fire Barrier Material Special Review Team Final Report Findings, Current Fire
Endurance Testing, and Ampacity Calculation Errors," in which it discussed the
safety implications of these questions.  On June 24, 1992, the NRC issued NRC
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."

Description of Circumstances

TU Electric and the NRC recently sponsored additional testing of 
Thermo-Lag 330 material.  

TESTS SPONSORED BY TU ELECTRIC

On August 19-21, 1992, TU Electric sponsored a second series of tests at the
Omega Point Laboratory to aid in qualifying its Thermo-Lag 330 electrical
raceway fire barrier systems for its Comanche Peak Steam Electric Station.  

This series of tests consisted of 1-hour fire endurance tests (using the ASTM
E-119 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 barriers were
installed on the test articles in accordance with TU Electric's Thermo-Lag
installation procedures.  TU Electric wrote these procedures based on vendor
recommended installation procedures.  

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 as required by TU procedures and as the system is installed in
the plant.  

The articles tested during this series of tests consisted of a conduit
configuration, which exposed five conduits of various sizes (3-inch, 2-inch,
1-1/2-inch and two 3/4-inch) to the same test fire, a 24-inch wide cable tray
with a T-section and a 30-inch wide cable tray.  

On August 19, 1992, TU Electric performed a 1-hour fire endurance test on the
conduit configuration.  The fire barrier systems installed on the 3-inch, 
2-inch and 1-1/2-inch conduits and their associated cable pull boxes were
constructed using 1-hour Thermo-Lag 330 conduit pre-shapes and panels,
respectively.  The 3/4-inch conduits were constructed using a Thermo-Lag 330
conduit pre-shape as a base material.  The two 3/4-inch conduits were divided
at the middle of the test specimen, and four different enhanced barrier
systems were tested.  The first of these consisted of a 3/4-inch conduit run,
one half of which was protected by a 3/4-inch Thermo-Lag 330 fire barrier
conduit pre-shape, and the other half protected with a 1/2-inch thick conduit .

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pre-shape with a wire mesh "stress skin" applied on the exterior and 1/4-inch
of trowel grade Thermo-Lag applied to the stress skin.  One half of the second
3/4-inch conduit run was protected by a 1/2-inch thick conduit pre-shape with
a 1/4-inch thick Thermo-Lag flexi-blanket wrap.  The other half was protected
by a 1/2-inch thick conduit pre-shape with a 1/4-inch thick pre-shape overlay. 
TU Electric did not conduct a hose stream test after the fire endurance test. 
The post-fire visual inspection of the test specimen revealed that the
interface joints between the vertical conduit runs and the cable pull boxes
had opened and exposed conduit metal surfaces to the fire.  In addition, the
cables exhibited visible fire damage to cable jackets in all conduits, except
for the 3/4-inch conduit protected by the 1/2-inch thick conduit pre-shape
with the 1/4-inch pre-shape overlay.   Throughout the fire endurance test, the
thermocouple temperatures on the cables inside the 3/4-inch conduit protected
by the overlay never reached 163 �C (325 �F).  All other conduit
configurations exceeded 163� (325 �F) on the cables during the test. 

On August 20, 1992, TU Electric sponsored a test of a 24-inch wide ladder back
tray with a T-tray configuration.  Post-fire inspection of this specimen
revealed that five joint and seam type openings had occurred.  These openings
were both in horizontal and vertical runs of the cable tray.  Fire damage to
the cables was also identified during the post-fire inspection, raising
questions whether the cables would have functioned properly during a fire. 
The thermocouples indicated that internal temperatures in certain areas of the
test article exceeded 163 �C (325 �F) at 47 minutes.  The maximum monitored
cable temperature during the test was 194 �C (381 �F). 

On August 21, 1992, TU Electric sponsored a test of a 30-inch wide ladder back
tray configuration.  During the post-fire inspection of this specimen, five
joint and seam type openings were identified in horizontal and vertical runs
of the cable tray.  The Thermo-Lag barrier also experienced areas of loss of
its material, leaving spots of bare stress skin covering the tray.  Fire
damage to the cables was identified during the post-fire inspection. 
Thermocouples indicated that internal temperatures in certain areas of the
test article exceeded 163 �C (325 �F) at 30 minutes.  The maximum monitored
cable temperature during the test was approximately 371 �C (700 �F). 

Although previous tests conducted by TU Electric (see Bulletin 92-01) resulted
in the apparent successful performance of large diameter conduits and narrow
trays, new information provided by these recent tests has led the NRC to
believe that potential early failures of Thermo-Lag barriers are not limited
to specific sizes.  The NRC considers the openings at the joints and seams of
the Thermo-Lag material to be of high significance.  The characteristics of
the configurations of the material protecting the trays or conduits in
question seemed to impact the effectiveness of the barrier material more than
their specific sizes.  The tests sponsored by TU Electric revealed that the
Thermo-Lag material lost its structural integrity primarily at the seams and
joints and that cable damage was most significant at these seam and joint
separations.  

Following the tests conducted in June 1992, the test assemblies were subjected
to hose streams which altered the conditions of the barriers.  Due to the hose
stream, post-fire inspection of these assemblies for joint failures and burn.

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through was prevented.  The assemblies tested in August 1992 were cooled with
water, essentially leaving the test assemblies in the condition they were in
at the completion of the fire test.  Areas of burn through and seam and joint
failures were observed during post-fire inspection.

Further, the TU Electric assemblies tested in June 1992 were constructed using
supports that were covered with two layers of Thermo-Lag material.  The
assemblies tested in August 1992 had supports which were insulated to only 
9 inches, corresponding to the TU Electric actual plant installations.  Thus,
the June 1992 tests did not model the installed plant configuration, as was
the case in the August 1992 tests.

TESTS SPONSORED BY THE NRC  

On July 15 and 17, 1992, the NRC sponsored a series of "small scale" fire
endurance tests on 1- and 3-hour Thermo-Lag 330 pre-formed fire barrier panels
at the National Institute of Standards and Technology (NIST).  On
July 27, 1992, the NRC issued  the results of the first series of small scale
tests in IN 92-55, "Current Fire Endurance Test Results for Thermo-Lag Fire
Barrier Material."  On August 6-7 and 14, 1992, the NRC sponsored a second
series of 1- and 3-hour small scale fire endurance tests on Thermo-Lag 330
fire barrier pre-formed panels.  

On July 15, 1992, the NRC sponsored a 1-hour fire endurance test.  The 1-hour
panel stress skin was oriented away from the fire exposure, according to
vendor recommendation.  The average thermocouple reading on the unexposed
surface exceeded 162.7 �C (325 oF) in approximately 22 minutes, and the
unexposed surface of the material reached an average temperature of 652 �C
(1206 oF) at 45 minutes.  The unexposed surface of the material exhibited
visible browning in 35 minutes.  During the test, the thermocouple on the
unexposed surface reached a peak reading of 935 oC (1716 oF), exceeding the
corresponding furnace temperature of 923 �C (1694 oF), as the material burned
and added heat to the baseline furnace temperature.  The panels burned through
at two locations in 46 minutes, resulting in a corresponding drop in surface
thermocouple readings as the cold air entered the furnace.  After 1 hour,
approximately 85 percent of the unexposed surface was blackened.  

On July 17, 1992, the NRC sponsored a 3-hour test.  The 3-hour panels had
stress skin installed on both sides of the Thermo-Lag material.  To prepare
for the test, the technicians installed the ribbed side of the specimen on the
unexposed side with the non-ribbed side of the material towards the furnace
side.  The stress skin on the furnace side of the specimen was restrained by
the furnace specimen support lip during the test.  The average thermocouple
reading exceeded 162.7 �C (325 oF) in 2 hours and 20 minutes, the average
temperature at the end of 3 hours was 206 �C (403 oF), and the peak of
thermocouple reading was 222 �C (432 oF).  After the test, the material was
soft and exhibited plastic deformation, and the fire-exposed stress skin
crumbled upon contact.  Nevertheless, visible signs of damage on the unexposed
side were limited to off-gassing, slight browning, and crystallization at the
surface.  .

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On August 5, 1992, the NRC sponsored a fire endurance test on a 3-hour Thermo-
Lag fire barrier panel, which had stress skin on both sides.  The edges of the
stress skin of the 3-hour material were cut away from the exposed side of the
panel so that the outer edges of the stress skin contacted the support lip of
the furnace.  The stress skin was kept from being restrained in compression at
the edges of the panel around the lip of the furnace.  The average
thermocouple temperature of the unexposed surface exceeded the ASTM E-119
temperature acceptance criterion of 163 �C (325 �F) in 45 minutes.  After 
1 hour, the unexposed surface temperature reading was 756 �C (1392 �F).  At 
1 hour and 20 minutes, the panel was burned through.  This 3-hour
configuration performed quite differently during this test than did the
Thermo-Lag 330 fire barrier panel in the July 17, 1992, 3-hour fire test in
which the stress skin was restrained on the side exposed to the fire.  In this
previous test, the average unexposed surface temperature of the restrained
specimen did not exceed 163 �C (325 �F) until 2 hours and 20 minutes into the
test, and the maximum temperature at the end of the 3-hour test was 194 �C
(381 �F).  The specimen tested on July 17, 1992 did not burn through. 

On August 6, 1992, the NRC sponsored a second 1-hour fire endurance test on a
Thermo-Lag 330 1-hour panel, which had stress skin on one side only.  This
panel was placed on the furnace with the stress skin towards the fire,
although the vendor recommends that the 1-hour panel be installed with the
stress skin away from the fire exposure.  The deviation from the vendor
recommendation aided in the determination of the material's sensitivity to
installation variations.  The stress skin was restrained by the furnace
specimen support lip.  The average unexposed surface temperature of the
specimen exceeded 163 �C (325 �F) in 34 minutes, and at 1 hour, the maximum
temperature of the unexposed surface was 237 �C (458 �F).  However, the
specimen was not burned through.  The performance of the specimen in this test
was superior to the specimen tested on July 15, 1992, at which the stress skin
faced the unexposed side, as recommended by the vendor.  The specimen tested
on July 15, 1992, exceeded the 163 �C (325 �F) acceptance criterion in 20
minutes and the unexposed surface reached 649 �C (1200 �F) in 37 minutes. 
Burn through was observed in 46 minutes.

On August 7, 1992, the NRC sponsored a third 3-hour fire endurance test.  Two
1-hour fire barriers were dry fitted together with their stress skins on the
outer sides of the test specimen.  As in the test conducted on August 5, the
exposed side stress skin was trimmed away to prevent the material from being
restrained.  One hour into the test, the specimen abruptly began releasing
gases, and the thermocouple readings inside the furnace indicated that the
thermocouple had come into contact with burning material.  The average
thermocouple reading exceeded 163 �C (325 �F) in 1 hour and 26 minutes.  After
2 hours, burn holes were observed in several locations.  After the burn holes
formed, unexposed surface thermocouple readings oscillated dramatically, with
a peak reading of 947 �C (1737 �F) at the end of the test.  Nonetheless, this
test specimen performed better than did the prefabricated 3-hour panel with
its stress skin trimmed away.  

On August 14, 1992, the NRC sponsored a final 3-hour test, again using two
1-hour panels dry fitted together with their stress skins on the outer sides
of the test specimen.  The stress skin was not trimmed away from the specimen .

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for this test; it was restrained in compression at the edges of the panel. 
The average thermocouple reading exceeded 163 �C (325 �F) in 2 hours and 
40 minutes and reached 176 �C (349 �F) at the end of the test.  Visible signs
of damage were limited to off-gassing and slight crystallization at the
surface of the unexposed side, and no browning was observed.  

The following table summarizes the data collected during these small scale
tests.


Test     Barrier     Stress        Stress         Time to         Burn 
Date     Rating       Skin          Skin        Exceed 163 �C*   Through
                    Restraint    Orientation     (hrs:min)      (hrs:min)

7/15/92  1 hour       N/A         unexposed        0:22           0:46
8/06/92  1 hour    restrained      exposed         0:34           none
7/17/92  3 hour    restrained     both sides       2:20           none
8/05/92  3 hour    unrestrained   both sides       0:45           1:20
8/07/92  3 hour**  unrestrained   both sides       1:26           2:03
8/14/92  3 hour**  restrained     both sides       2:40           none

*  Average unexposed surface thermocouple temperature
** Two 1-hour panels fitted face to face

In IN 92-55, the staff listed specific furnace specifications and test
assembly parameters used in both series of tests conducted by NIST.

The NRC views the results of the NIST tests as indicative of an inability of
the Thermo-Lag material itself to provide protection according to its
specified fire resistive rating, depending on its configuration.  The tests
conducted at NIST were not considered definitive in that the tests were not
full scale and only panels were tested.  However, the information gleaned from
the tests provided enough evidence to the NRC to confirm doubts raised during
the TU Electric tests, such as the bare stress skin observed following the TU
30-inch wide cable tray test on August 21, 1992, discussed above, leading to a
conclusion that Thermo-Lag fire barriers should be treated as inoperable in
the absence of successful, applicable plant specific tests.

Discussion

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 fire
protection plan that satisfies Appendix A to 10 CFR Part 50, General Design
Criteria (GDC) 3, "Fire Protection."  GDC 3 requires that 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.  10 CFR 50.48(b) states that Appendix R to
10 CFR Part 50 establishes fire protection features required to satisfy .

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Criterion 3 of Appendix A to 10 CFR Part 50 for certain generic issues for
nuclear power plants licensed to operate before January 1, 1979. 
Sections III.G, III.J, and III.0 of Appendix R apply to nuclear power plants
licensed to operate before January 1, 1979.  In 10 CFR 50.48(e), the NRC
requires that all licensees for plants licensed to operate after
January 1, 1979 shall complete all fire protection modifications needed to
satisfy Criterion 3 of Appendix A to 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 damage.  

To ensure that electrical cables 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,
a fire detection and an automatic fire suppression system shall be installed
in the fire area.  

Under fire conditions, the thermal degradation of fire barrier systems (e.g.,
walls, floors, equipment vaults, and electrical raceway enclosures), 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 or shutdown conditions. 

The NRC considered the apparent failures of the recent Thermo-Lag fire barrier
fire endurance tests and determined that the 1- and 3-hour pre-formed
assemblies installed on conduits, cable trays (of all sizes and
configurations), and used to construct fire barrier walls and ceilings, and
equipment enclosures do not provide the level of safety as required by NRC
requirements.  The tests sponsored by TU Electric raised concerns relating to
joint and seam separation leading to cable damage.  In addition, they raise
concerns about the potential for burn through of the Thermo-Lag material
itself.  The tests sponsored by the NRC appear to confirm concerns relating to
burn through of the Thermo-Lag material in certain configurations in the
absence of joints and seams.

Requested Actions

All holders of operating licenses for nuclear power reactors, immediately upon
receiving this bulletin supplement, are requested to take the following
actions.  These actions are essentially the same as those listed in Bulletin
92-01, but the scope has been expanded to include all sizes of conduits and
trays and to include walls, ceilings, and equipment enclosures.

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.

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      Thermo-Lag 330 fire barrier material installed and determine the plant
      areas which use this material for the protection and separation of the
      safe shutdown capability. 

2.    In those plant areas in which Thermo-Lag fire barriers are used in
      raceways, walls, ceilings, equipment enclosures, or other areas to
      protect cable trays, conduits, or separate redundant safe shutdown
      functions, the licensee should implement, in accordance with plant
      procedures, the appropriate compensatory measures, such as fire watches,
      consistent with those that would be implemented by either the plant
      technical specifications or the operating license for an inoperable fire
      barrier.  These compensatory measures should remain in place until the
      licensee can declare the fire barriers operable on the basis of
      applicable tests which demonstrate successful 1- or 3-hour barrier
      performance.

Although the specific details of this supplement to Bulletin 92-01 may not
apply to holders of construction permits for nuclear power reactors, it is
requested that the general concerns of this bulletin supplement be reviewed
for current or future applicability.  

Required Report

Each licensee who has installed Thermo-Lag 330 fire barriers must inform the
NRC in writing within 30 days of receiving this bulletin supplement, whether
or not it has taken the above actions.  Where fire barriers are declared
inoperable, the licensee is required to describe the measures being taken to
ensure or restore fire barrier operability.  These measures should be
consistent with actions taken in response to Bulletin 92-01.


Backfit Discussion

These types of fire barriers are 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 supplement 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, the NRC is issuing this bulletin supplement as a compliance backfit
under 10 CFR 50.109(a)(4).  

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 120 person hours for each licensee response, including those
needed to assess the new recommendations, search data sources, gather and.

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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 (3150-0012), Office of Information and Regulatory Affairs,
NEOB-3019, Office of Management and Budget, Washington, D.C. 20503.

Although no specific response is required for the following information, the
following information would assist the NRC in evaluating the cost of complying
with this bulletin supplement:

(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 and
      documentation;

(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.


                                  ORIGINAL SIGNED BY


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


Technical contacts:  Ralph Architzel, NRR
                     (301) 504-2804

                     Patrick Madden, NRR
                     (301) 504-2854

Attachment:  
List of Recently Issued NRC Bulletins.

 

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