United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 95-49: Seismic Adequacy of Thermo-Lag Panels

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                     OFFICE OF NUCLEAR REACTOR REGULATION
                          WASHINGTON, D.C. 20555-0001

                               October 27, 1995


NRC INFORMATION NOTICE 95-49:  SEISMIC ADEQUACY OF THERMO-LAG PANELS


Addressees

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

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to inform addressees about two specific concerns related to the use of
Thermo-Lag 330-1 fire barrier material:  (1) actual properties of the
mechanical material could be significantly different than the numerical values
used (or provided) by the vendor to demonstrate the seismic adequacy of
Thermo-Lag 330-1 panels and (2) the actual weights of the installed Thermo-Lag
panels could be appreciably higher than the weights calculated from the
minimum thickness.  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

A July 21, 1992, petition filed by the Nuclear Information and Resource
Service (Accession Number 9208280125) raised a "seismic issue" regarding the
Thermo-Lag fire barrier.  In response, the staff studied the issue and
concluded that the "shattering of raceways or severing of cables required for
safe shutdown are not credible scenarios" (letter from T. Murley to          
M. Mariotte, February 1, 1993 [Accession Number 9302110146]) under postulated
seismic events at nuclear power plant sites.  The staff response was based on
acceptance of the analyses performed by a consultant of Thermal Science,
Incorporated (TSI).  TSI, which manufactures and supplies Thermo-Lag fire
barrier material, provided the consultant with the mechanical properties of
Thermo-Lag.

On November 11, 1994, the Tennessee Valley Authority (TVA) submitted the
results of simulated seismic tests and mechanical properties tests related to
the use of Thermo-Lag fire barrier material at Watts Bar Nuclear Plant
(Accession Number 9411250234).  These tests indicated significantly lower
mechanical properties values compared to those used by the TSI consultant.

During the staff review of the application for an operating license for
Comanche Peak Steam Electrical Station, Unit 2, the issue of uncertainties in
the weight of Thermo-Lag panels arose.

9510240388.                                                            IN 95-49
                                                            October 27, 1995
                                                            Page 2 of 4


Discussion

The regulations that address the need for fire protection at nuclear power
plants, that is, 10 CFR Section 50.48; Part 50, Appendix A, General Design
Criterion 3; and Part 50, Appendix R, do not explicitly require fire barriers
to be seismically qualified (i.e., to maintain their integrity after
postulated seismic events).  However, provision C.2 of Regulatory Guide 1.29,
"Seismic Design Classification," addresses the issue of seismic Category II
versus seismic Category I.  In that context, a fire barrier is considered to
be seismic Category II.  Based on these provisions, the fire barriers are
allowed to undergo damage during the postulated seismic events.  However, the
fire barriers should not be damaged to such an extent that they could reduce
the functioning of the protected cables or other safety-related structures,
systems, or components.

Two specific issues are discussed in the following paragraphs:

Seismic Adequacy of Thermo-Lag Fire Barrier

      The seismic adequacy of various configurations of Thermo-Lag panels
      attached to the raceways has been determined by static analyses of the
      configurations, which were subjected to simultaneous horizontal and
      vertical accelerations of up to 7.5g and 5.0g, respectively.  The
      analyses were performed by a TSI consultant using the mechanical
      properties (i.e., tensile strength, shear strength, and corresponding
      moduli) at various temperatures provided by TSI.  The consultant
      concluded that the panels and conduit wraps were seismically adequate. 
      On the basis of its review of these analyses, the staff concluded that
      properly installed Thermo-Lag panels and conduit wraps would not undergo
      appreciable damage during the postulated seismic events at the nuclear
      reactor sites.  Because of the nonductile nature of the material,
      Thermo-lag panels and conduit wraps might crack and crumble into small
      fragments or powder under a strong vibratory motion; however, they would
      not cause damage to the protected raceways or other safety-related
      components or equipment in the vicinity of the raceways.  

      The November 1994 TVA submittal provided the results of mechanical
      properties tests related to the use of Thermo-Lag fire barrier material
      at Watts Bar Nuclear Plant.  A comparison showed that the TVA-tested
      mechanical properties values were considerably lower than those used by
      the TSI consultant [Accession Number 9208260065].  Enclosure 2, of the
      TVA submittal shows, for example, that the average tensile strength of
      the 1.59-cm-thick [5/8-in.] Thermo-Lag panel at 53 �C (127 �F) varies
      between 2.38 megapascals (Mpa) [345 pounds per square inch (psi)] and
      3.36 Mpa (488 psi), while the TSI consultant used 4.96 Mpa (720 psi).  .                                                            IN 95-49
                                                            October 27, 1995
                                                            Page 3 of 4


      In December 1994, pursuant to 10 CFR 50.54(f), NRC sent followup letters
      to Generic Letter (GL) 92-08, "Thermo-Lag 330-1 Fire Barriers," to the
      licensees and construction permit holders that had used Thermo-Lag 330-1
      fire barrier in their plants.  These letters included a request for
      additional information and some background information.  Item 1(9)
      requested information related to the mechanical properties of the
      Thermo-Lag material.  A number of responses indicated that the licensees
      depended on the analyses performed by the TSI consultant.

      Enclosure 1 of the November 1994 letter from TVA contains the results of
      the seismic testing performed by Wyle Laboratories of Huntsville,
      Alabama, for selected configurations of raceways with the Thermo-Lag
      panels installed.  TVA sponsored the seismic tests and the mechanical
      properties tests to ensure (through shake-table testing and analyses)
      that Thermo-Lag will not adversely affect the safety performance of
      related equipment, for example, cables and cable trays.  The staff
      review of the test results and of supplementary analyses performed by
      TVA indicates that the Thermo-Lag 330-1 fire barrier, when installed in
      accordance with the TVA installation procedure, will be able to
      withstand the postulated seismic events at the TVA Watts Bar plant
      without adverse effects on the safety-related systems and components. 

Variation in Weight of the Fire Barrier Material

      A review of the "as received" weights of Thermo-Lag 330-1 panels,
      prefabricated conduit sections, and 330-660 flexi-blanket fire barriers
      indicated that there could be a variation of as much as 45 percent in
      the unit weights of the fire barriers when calculated as a percentage of
      the weight associated with the thickest panel (maximum weight).  The
      variation is primarily related to the variation in the thickness
      tolerances.  For example, the thickness of a 1-hour-rated panel could
      vary between 1.27 cm [1/2 in.] and 1.91 cm [3/4 in.], thus indicating a
      variation of 33 percent.  The remaining 12-percent variation could
      result from the variation in the density of the material.  The weight of
      one layer of stress skin, staples, steel bands, and trowel-grade
      material (applied during the installation) can increase the average
      weight of a panel by about 10 percent.  Depending on the method used by
      licensees in incorporating the weight of the Thermo-Lag fire barrier in
      seismic analysis of the raceways and their supports and anchorages, the
      effects of the variations could be nonconservative when the maximum unit
      weight of the fire barrier and its accessories (wire mesh, staples,
      bands) is higher than the nominal values considered in determining the
      loads on the raceways and their supports and anchorages.

Summary reports that are submitted to address the seismic adequacy of the
electrical and mechanical equipment in accordance with GL 87-02 and  
Supplement 1 to GL 87-02, "Verification of Seismic Adequacy of Mechanical and
Electrical Equipment in Operating Reactors," dated February 19, 1987 and    
May 22, 1992, respectively, will be reviewed by the staff who will consider
the effects of the fire barriers in assessing the integrated safety of the
raceway systems and other equipment..                                                            IN 95-49
                                                            October 27, 1995
                                                            Page 4 of 4


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 DMCrutchfield


                                    Dennis M. Crutchfield, Director
                                    Division of Reactor Program Management
                                    Office of Nuclear Reactor Regulation

Technical contact:  Hans Ashar, NRR
                    (301) 415-2851
Page Last Reviewed/Updated Monday, November 18, 2013