ML20199H593

Safety Evaluation Accepting Thermo-Lag Re Ampacity Derating Issues for Plant

ML20199H593
Person / Time
Site:	Davis Besse
Issue date:	01/20/1999
From:	NRC (Affiliation Not Assigned)
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ML20199H588	List: ML20199H582 ML20199H593
References
NUDOCS 9901250247
Download: ML20199H593 (3)

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1. At O  % UNITED STATES i l

, s* g NUCLEAR REGULATORY COMMISSION

• WASHINGTON, D.C. 20066 4001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMPACITY DERATING ISSUES FIRSTENERGY NUCLEAR OPERATING COMPANY DAVIS-BESSE NUCLEAR POWER STATION. UNIT NO. 1 DOCKET NO. 50-346

1.0 INTRODUCTION

By letter dated November 5,1996, Toledo Edison Company, Centerior Service Company, and The Cleveland Electric Illuminating Company (the licensees for the Davis-Besse Nuclear Power Station at that time), submitted their response to the NRC Request for Additional Information (RAI) dated October 9,1996, related to cable ampacity derating due to application of Thermo-Lag fire barriers at Davis-Besse. (On January 1, 1999, FirstEnergy Nuclear Operating Company became the licensed operator of Davis-Besse.)

Discussions were held with the licensees during a conference call with the NRC staff on January 14, 1997, and during a meeting with the NRC staff on April 3, 1997. During the April 3, 1997, meeting, the licensees stated that there are adequate ampacity margins for the Thermo-Lag installations, even considering the need to incorporate additional conservatism as a result of the discussions with the NRC staff. The licensees indicated that the associated calculations would be revised to include the load factor for different types of equipment, and to account for conduit grouping factors. On September 10, 1997, the licensees submitted an updated evaluation of ampacity issues related to Thermo-Lag fire barriers for Davis-Besse. The licensees stated that this updated evaluation incorporated a load factor for different types of equipment and conduit grouping factors as needed and completely superseded the previous evaluation. The licensees stated that there is adequate margin to accommodate the ampacity derating due to application of Thermo-Lag 330-1, from the time it was installed to the time it is eventually removed, such that the insulation properties of the protected catd:s are not adversely impacted.

The licensees awarded a contract to Peak Seals, Incorporated, to perform Thermo-Lag replacement using 3M Company Interam materials for 1-hour and 3-hour rated fire barriers and for radiant energy shields. The licensees will use test data for the alternate material to confirm that there is an adequate margin to accommodate the ampacity derating due to application of the alternate material, and will revise the applicable plant-specific calculations.

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2.0 EVALUATION l After reviewing the licensees' submittals, the staff agrees that the licensees adequately addressed the staff's concerns raised in the RAI dated October 9, 1996.

The licensees performed an ampacity derating calculation utilizing the following:

1. Obtain base ampacity value from the appropriate industry standard.

2. Correct the base ampacity value to account for the difference between the ambient temperature for which the base ampacity value

, is valid and the normal design temperature for the plant area in l which the cable is located, utilizing the appropriate factor provided in the industry standard.

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( 3. Apply an additional derating factor to account for multiple I conductors within the raceway, if applicable, utilizing the appropriate factor provided in the industry standard.

4. Apply an additional derating factor to account for the conduit j grouping factor, as applicable for groups of closely spaced conduits, utilizing the appropriate factor provided in the industry standard.

5. Apply an additional derating factor to account for the presence of l the fire barrier, utilizing data provided by the fire barrier

! manufacturer.

6. Confirm that the resulting (derated) ampacity exceeds the load current. Load current for motors are based on 125% of the nameplate ratings.

The licensees' letter dated June 13, 1995, listed the raceway applications at Davis-Besse which utilized Thermo-Lag 330-1 fire wrap material, including 1-hour-rated fire barrier applications for conduits, 3-hour-rated fire barrier applications for conduit, and 1/2-hour-rated radiant energy shield applications. Thermo-Lag 330-1 is not utilized in cable tray applications at the plant.

The licensees stated that the 1/2-hour-rated and 1-hour-rated configurations compare favorably with the tested configurations at Texas Utilities Electric Company (TVE). The 3-inch conduit size is enveloped by the 3/4-inch, 2-inch, and 5-inch conduit sizes tested. The tested configurations have an equal or l slightly greater thickness of Thermo-Lag material than the Davis-Besse configurations, which is conservative. The use of the 350 topcoat on the tested configurations should be slightly conservative. Also, the tested configurations were an upgraded design, with additional material applied at d

joints and seams. The Omega Point Laboratories test report provided a bounding ampacity derating factor of 11%. The TUE Comanche Peak Steam Electric Station, Unit 2, added an additional 10% to bound test protocol i

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! uncertainties identified after the tests were completed. Davis-Besse also l l applied the ampacity derating factor of 21% for 1-hour-rated application. The  ;

ampacity derating factor of 21% is also considered conservatively applicable for box configurations such as the 1/2-hour-rated radiant energy shields located in the containment annulus, since the larger surface area of the box would improve heat transfer. For a stacked conduit configuration, Davis-Besse l adds an additional 9% margin resulting in an ampacity derating factor of 30% l which is also utilized by TUE for conduit / cable tray configurations. l The Davis-Besse 3-hour-rated configurations compare favorably with 1-inch and 4-inch conduit tested configurations at the Tennessee Valley Authority (TVA).

The 4-inch conduit size is enveloped by the sizes tested at TVA. Though the tested configuration includes an overlay of Thermo-Lag 770-1 mat material, this upgrade configuration is conservative. The licensees stated that a 350 I topcoat is applied to a small length of Thermo-Lag in Room 114. However, no l topcoat was utilized in the tested configurations. This difference should be l slightly less conservative and have only a minimal effect on results.

l The tested configurations utilized post-caulking of the joints and seams rather than pre-caulking. This would not be expected to have an appreciable effect on results since all gaps were filled in. The overlay applied should also serve to prevent any vent paths. The Omega Point Laboratories test report provided a bounding ampacity derating factor of 13%. TVA applied an )

additional 5% factor to the bounding 13% ampacity derating factor resulting in j a total 18% ampacity derating factor to bound various test uncertainties. The l licensees stated that they applied the ampacity derating factor of 28%

(additional 10% for conservatism) for 3-hour-rated applications. For a  !

stacked conduit configuration an additional 9% margin is added, resulting in '

an ampacity derating factor of 37% for 3-hour-rated stacked conduit applications.

As a result of this review, several cables were identified which had load currents in excess of their derated ampacities. The licensees provided adequate justification for acceptability of these cables.

3.0 CONCLUSION

Based on the above evaluation, the staff concludes that no significant safety hazards are introduced through use of the licensees' ampacity derating methodology. Therefore, there are no ampacity related safety concerns at Davis-Besse for the specified applications.

Principal Contributor: A. Pal Date: January 20, 1999 i

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