United States Nuclear Regulatory Commission - Protecting People and the Environment

Investigation of Twenty-Foot Separation Distance as a Fire Protection Method as Specified in 10 CFR 50, Appendix R (NUREG/CR-3192)

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Publication Information

Date Published: October 1983

Prepared by:
Douglas D. Cline,
Walter A. von Riesemann
James M. Chavez

Sandia National Laboratories
Albuquerque, NM 87185
operated by Sandia Corporation
for the US Department of Energy


Prepared for:
Division of Engineering Technology
Office of Nuclear Regulatory Research
US Nuclear Regulatory Commission
Washington, DC 20555
Under Memorandum of Understanding DOE 40-550-75

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A combined experimental/analytical program was conducted to examine the adequacy of the 20-foot separation requirement, one of the requirements set forth in Appendix R of 10 CFR 50 for the fire protection of redundant safety systems that are necessary to achieve hot shutdown in nuclear power plants. Specifically, Sections III.G.2.b and d of Appendix R require separation of the redundant safety systems by a horizontal distance of more than 20 feet with no intervening combustibles or fire hazards. Section III.G.2.b also requires installation of fire detectors and an automatic fire suppression system within fire areas. The experimental investigation consisted of six full-scale fire tests of unqualified and qualified electrical cables separated by 20 feet with (1) no protection, (2) protection with a ceramic fiber blanket and sheet metal covers on the cable trays, and (3) protection with a fire protective coating. For the test conditions investigated, all unqualified cable electrically shortened while qualified cable was found to short only when left unprotected.

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