Aging Effects on Fire-Retardant Additives in Organic Materials for Nuclear Plant Applications (NUREG/CR-2868, SAND82-0485)
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Manuscript Completed: August 1982
Date Published: August 1982
Roger L. Clough
Sandia National Laboratories
Albuquerque, New Mexico 87185
Operated by Sandia Corporation
for the U.S. Department of Energy
Under Contract No. DE-AC04-76DP00789
Electrical Engineering Branch
Division of Engineering Technology
Office of Water Reactor Safety Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
Under Interagency Agreement DOE 40-550-75
NRC FIN A-1051
Inhibiting fire is a major concern of nuclear safety. One of the most widely used commercial fire-retardant additives incorporated into cable insulation and other organic materials to reduce their flammability has been the halocarbon (usually a chlorinated hydrocarbon), typically in combination with antimony oxide. Such materials may be installed for the design lifetime of a nuclear plant; this report describes an investigation of the long-term aging behavior of these fire-retardant additives in polymeric materials.
Extensive aging experiments on fire-retarded formulations of ethylene propylene rubber (EPR) and of chlorosulfonated polyethylene (CSPE) have been carried out, with chemical analysis of halogen and antimony content performed as a function of aging time and conditions. Oxygen index flammability measurements were also performed on selected samples. Significant fire-retardant losses (both chlorine (Cl) and antimony (Sb)) were found to occur in certain of the fire-retardant materials but not in others, depending on the molecular structure of the particular halogen-containing component. The Cl:Sb loss ratios indicate that a chemical reaction takes place under the aging conditions to form the volatile compound, antimony trichloride (SbC1 3). The EPR formulations showed a modestly increased flammability with fire-retardant loss on aging. CSPE materials exhibited a significant decrease in flammability on aging despite the loss of flame retardants. This appears to be correlated with the loss of flammable, volatile components from the formulation.
Using the activation energy of 34 kcal/mol derived from Arrhenius treatment of the antimony loss data for the EPR formulation having the most rapid loss rate, it is predicted that fire-retardant loss should become appreciable for this material only at substantially elevated temperatures or exceedingly long times. The data indicate that the loss of halogen- and antimony-based fire retardants appears to be insignificant under ambient conditions expected for nuclear plants.