United States Nuclear Regulatory Commission - Protecting People and the Environment

The Impact of Thermal Aging on the Flammability of Electric Cables (NUREG/CR-5619, SAND90-2121)

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Publication Information

Manuscript Completed: February 1991
Date Published:
March 1991

Prepared by:
Steven P. Nowlen
Sandia National Laboratories
P.O. Box 5800
Albuquerque, New Mexico 87185-5800
Operated by Sandia Corporation

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

NRC FIN A-1833

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Abstract

An investigation of the impact of thermal aging on the flammability of two common types of nuclear grade electrical cables has been performed. Four large-scale flammability tests were performed with each of the two cable types tested in both an unaged (i.e., new off the reel) and a thermally aged (artificially aged) condition. In all cases, the fire was observed to consume virtually all of the combustible cable jacket and insulation material present. However, for both cable types tested, the thermal aging process caused a decrease in the cable flammability as demonstrated by decreases in the rate of fire growth, peak fire intensity, total heat released and near fire temperatures. This result is consistent with past cable aging studies because it has been observed that the thermal aging process will drive off certain of the more volatile constituents of a polymeric material. Presumably, when these aged materials are subjected to a fire, the evolution of volatile combustible gases is reduced as compared to the unaged materials, and hence, flammability is reduced. The results of these tests indicate that, at least for the two cable types tested, the evaluation of cable flammability using unaged cable samples will remain a conservative indicator of cable flammability in a thermally aged condition.

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