Information Notice No. 95-49

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Home > Electronic Reading Room > Document Collections > General Communications > Information Notices > 1995 > IN 95-49

 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

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UNITED STATES NUCLEAR REGULATORY COMMISSION
Information Notice No. 95-49

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 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 øC (127 øF) 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
Information Notice No. 95-49

file:////acfnas/perm/netsite-docs/gpo5444/in95049.html[4/18/2018 2:58:07 PM]

Technical contact: Hans Ashar, NRR

 (301) 415-2851