Ampacity Derating and Cable Functionality for Raceway Fire Barriers (NUREG/CR-6681)

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Publication Information

Manuscript Completed: July 2000
Date Published:
August 2000

Prepared by:
S. Nowlen

Sandia National Laboratories
P.O. Box 5000
Albuquerque, NM 87185-0748

R. Jenkins, NRC Project Manager

Prepared for:
Division of Engineering
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

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This report discusses two topical areas associated with localized fire barrier cladding systems for cables and cable raceways, namely, ampacity derating and cable functionality. Ampacity is defined as the electrical current carrying capacity of a particular cable in a given set of routing and environmental conditions. Ampacity derating refers to the process by which cable electrical current carrying limits are reduced in order to compensate for the thermal insulating effects of a raceway fire barrier cladding system. Cable functionality refers to the practice of assessing fire endurance ratings for a raceway fire barrier based on an assessment of the protected cables' ability to perform their intended design function before, during, and after the fire endurance exposure.

The discussions are based on experience and insights gained through reviews sponsored by the U. S. Nuclear Regulatory Commission (USNRC) of related licensee submittals. These reviews were conducted between 1994 and 1999 and involved a total of 23 USNRC licensees and numerous individual licensee submittals. In each topical area, the report provides general technical background, discusses currently applied methods of assessment, and identifies potential technical issues that may arise in the application of each assessment method. The report also provides guidance to assist the USNRC staff in reviewing and assessing licensee submittals in each area.

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