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

December 10, 1997

**Addressees**

All holders of operating licenses for nuclear power reactors.

**Purpose**

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to inform addressees about the resultsof mechanical properties testing of Thermo-Lag 330-1 fire barrier material performed by the National Institute of Standardsand Technology (NIST). The results of the testing indicated significantly lower mechanical properties than those used bythe vendor to demonstrate the seismic adequacy of Thermo-Lag 330-1 panels. It is expected that recipients will review theinformation for applicability to their facilities and consider actions, as appropriate. However, suggestions contained in thisinformation notice are not NRC requirements; therefore, no specific action or written response is required.

**Description of Circumstances**

In response to a "seismic issue" concern raised by the Nuclear Information and Resource Service regarding the Thermo-Lagfire barrier (Accession Number 9208280125), the staff studied the issue and concluded that the "shattering of raceways orsevering of cables required for safe shutdown were not credible scenarios" under postulated seismic events at nuclearpower plant sites (Accession Number 9302110146). The staff's response was based on acceptance of the analysesperformed by a consultant who used mechanical properties data for Thermo-Lag, which were provided by ThermalScience, Incorporated (TSI), the manufacturer and supplier of the Thermo-Lag fire barrier material.

The Tennessee Valley Authority (TVA) subsequently submitted the results of its 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.

The NRC staff, therefore, contracted with the NIST to perform appropriate mechanical properties testing of Thermo-Lagmaterial. The tests, test methods, and test results are described in the NIST's letter report to NRC entitled "MechanicalProperties of Samples of a 'Subliming' Fire Barrier Panel Material as a Function of Temperature (Accession Number9608140068)." NIST also compared its test results with TSI's and TVA's. NIST's test results for mean tensile strength,flexural strength, and elastic modulus of the 1-hour fire-rated Thermo-Lag material were at least 40 percent lower thanTSI's at 23 C (73 F) and 50 C (122 F). NIST's test results were similar to those of TVA.

**Discussion**

As stated in Information Notice (IN) 95-49, "Seismic Adequacy of Thermo-Lag Panels," dated October 27, 1995(Accession Number 9510240388), fire barriers may undergo damage during postulated seismic events, but 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. Therefore, NRC is concerned that the correct or conservative values forpertinent mechanical properties may not have been used in evaluating the seismic adequacy of Thermo-Lag panels and, as aresult, the fire barriers may not maintain their integrity during postulated seismic events.

The following is a summary comparison of the mechanical properties of Thermo-Lag 330-1 reported by TSI and NIST forthe 1-hour fire-rated material at 50 C (122 F):

NIST summarizes the results as follows: "The mean values of the mechanical properties measured in this study are lowerthan those reported by the manufacturer in Technical Note 90181. Some of the differences can be attributed, in part, to thedifferent testing methods that were used. However, the differences are sufficiently large to indicate that there are realdifferences between the tensile strength, flexural strength, and static modulus of elasticity of the samples used in the studyby NIST and those used in the manufacturer's tests."

A reevaluation by the NRC staff of Thermo-Lag stresses under postulated seismic events, using NIST's test results,indicated that at 23 C, properly installed [in accordance with TSI's installation procedure (see also IN 91-79, "Deficienciesin the Procedures for Installing Thermo-Lag Fire Barrier Material," and TSI's seismic evaluation criteria)] 1-hour fire-ratedThermo-Lag panels can safely withstand the seismic loadings imposed by 3.3 g vertical acceleration and 5.0 g horizontalacceleration ("g" being acceleration due to gravity). At 50 C, the corresponding acceleration levels are 1.2 g vertical and1.8 g horizontal (the g values indicated here are the spectral acceleration values at the location of the fire barrier material).

The Thermo-Lag fire barrier material has been removed from plants in high seismic areas (i.e., Diablo Canyon and SanOnofre), and it is the staff's judgment that the acceptable acceleration levels at 23 C (5.0 g horizontal, 3.3 g vertical) willnot be exceeded at the remaining operating plants during the design-basis seismic events. However, at higher sustainedtemperatures, the acceleration levels generated by design-basis seismic events at the locations of the Thermo-Lag protectedcable trays or equipment could exceed the acceptable acceleration levels at a number of operating nuclear power plants.The dynamic forces generated by such accelerations could detach the large pieces of Thermo-Lag panels from the cabletrays, which, in turn, could act as missiles and jeopardize the safety functions of the safety-related equipment andcomponents in the vicinity. However, the potential for such a hazard depends on the plant specific installation, spatialseparation, and sustained elevated temperature.

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.

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