ML20202B385

Safety Evaluation Addressing Thermo-Lag Related Ampacity Derating Issues.Ampacity Derating Analysis Results Acceptable

ML20202B385
Person / Time
Site:	Duane Arnold
Issue date:	01/26/1999
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20202B369	List: ML20202B367 ML20202B385 ML20202B389
References
GL-92-08, GL-92-8, NUDOCS 9901290066
Download: ML20202B385 (2)

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, }#"%i g UNITED STATES g ] NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20086-0001

% y SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION THERMO-LAG RELATED AMPACITY DERATING ISSUES lES UTILITIES INC.

DUANE ARNOLD ENERGY CENTER DOCKET NUMBERi 50-331

1.0 INTRODUCTION

By letters dated December 13,1996, and May 16,1997, IES Utilities Inc. (the licensee) submitted a response to the NRC Request for Additional information (RAI) related to Generic Letter (GL) 92-08, "Thermo-Lag 330-1 Fire Barriers," for the Duane Amold Energy Center (DAEC).

The licensee's o:iginal analyses which were the subject of the NRC RAI dated October 16, 1996, were based on an application of the ' Watts per foot" methodology. The preliminary review had iWicated that the subject methodology was inherently inadequate to demonstrate the accer'. ability of derived ampacity load limits for the cables installed at DAEC. Specifically, the subject methodology provided no assessment for the ampacity limits for an individual cable.

In addition, there were other concerns cited by the staff regarding the information provided in the licensee submittals dated February 14,1994, and June 2,1995.

In its December 13,1996, submittal, the licensee informed the staff that the Thermo-Lag barriers had been removed from all raceways containing continuously energized power cables. The licensee stated that only one fire barrier application involving continuously energized power cables at DAEC involves a Darmatt wrapped penetration. The licensee's May 16,1997, submittalincluded a new analysis to assess the ampacity loads for the Darmatt application.

The staff evaluation of the ampacity derating methodology for DAEC follows.

2.0 EVALUATION After reviewing the licensee's submittals and the Sandia National Laboratories (SNL) report, "A Technical Evaluation of the Duane Amold Energy Center Analysis of Ampacity Loads for Fire Barrier Clad Power Cables," dated September 15,1997 (Attached), the staff agrees with the SNL analyses and conclusions. The licensee assumed given the removal of the Thermo-Lag

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fire barriers at DAEC that further review of the licensee's original ' Watts per foot" methodology would not be necessary and the staff concurs with that assessment. This evaluation pertains only to the licensee calculation which assesses the ampacity limits for one Darmatt fire barrier.

Enclosure 9901290066 990126 #

PDR ADOCK 05000331 i P pop

. On the question pertaining to the licensee's definition of " continuously energized", the licensee responded that the definition pertained to any circuit that could be continuously energized, including control circuits, or circuits which had a "long duty cycle". In its submittal dated December 13,1996, the licensee stated that all pumps, compressors, fans, heaters "and the like" were treated as continuous loads.

The subject Darmatt fire barrier is a " boxed" enclosure jointly surrounding a pair of reactor building to drywell electrical penetration assemblies. The enclosure includes a number of conduits that enter into er pass through the fire barrier. One side of the " boxed" enclosure is represented by the concrete wall separating the drywell from the balance of the reactor building and the other sides are all comprised of Darmatt fire barrier material. The objective of the licensee's analysis is to estimate the operating temperature of the energized power cables that pass through the subject barrier.

SNL reviewed the Sargent & Lundy calculation included in the May 16,1997, submittal, and determined that the calculation was based on well founded and modem principles of heat transfer analysis. Although the SNL review was limited to ampacity derating methodology no mistakes in application and implementation were identified in the licensee submittals. SNL made certain supplemental observations regarding the licensee's methodology that provide qualitative support to its conclusion that the subject calculation is acceptable.

The licensee's calculation estimated that the maximum conductor temperature would be 56.5'C where the maximum allowable ampacity limit for the subject cable in the Darmatt barrier is 90*C, ,

Given the acceptability of the thermal model and the significant temperature margin estimated l by the subject calculation the staff finds that the licensee has demonstrated adequate ampacity margin for the specific application.

3.0 CONCLUSION

From the above evaluation, the staff concludes that no significant safety hazards are introduced through use of the licensee's ampacity derating methodology. Therefore, there are no ampacity related safety concerns at Duane Amold Energy Center for the specified applications.

Principal Contributor: R. Jenkins Date: January 26, 1999

Attachment:

SNL report, "A Technical Evaluation of the Duane Arnold Energy Center Analysis of Ampacity Loads for Fire Barrier Clad Power Cables," dated September 15, 1997.

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