Vulnerability of Nuclear Power Plant Structures to Large External Fires (NUREG/CR-3330, SAND83-1178)
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Manuscript Completed: August 1983
Date Published: September 1983
David E. Bennett
Sandia National Laboratories
Albuquerque, New Mexico 87185
Operated by Sandia Corporation
for the U.S. Department of Energy
Under Contract No. DE-AC04-76DP00789
Division of Risk Analysis
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
Under Memorandum of Understanding DOE 40-550-75
NRC FIN A-1214
This report examines the inherent vulnerability of nuclear power plant structures to the thermal environments arising from large, external fires. The inherent vulnerability is the capacity of the concrete safety-related structures to absorb thermal loads without exceeding the appropriate thermal and structural design criteria. The potential sources of these thermal environments are large, offsite fires arising from accidents involving the transportation or storage of large quantities of flammable gases or liquids.
A realistic thermal response analysis of a concrete panel was performed using three limiting criteria: temperature at the first rebar location, erosion and ablation of the front (exterior) surface due to high heat fluxes, and temperature at the back (interior) surface. The results of this analysis yield a relationship between incident heat flux and the maximum allowable exposure duration.
A simple fire analysis method was developed to predict the thermal flux incident upon a target as a function of range. A key feature is the use of an experimentally observed specific power emitted from the surface of large fires.
Example calculations for the break of a 0.91 m (3') diameter high-pressure natural gas pipeline and a 1 mZ hole in a 2-1/2 million gallon gasoline tank show that the resulting fires do not pose a significant hazard for ranges of 500 m or greater.