United States Nuclear Regulatory Commission - Protecting People and the Environment

Test Descriptions and Analysis of Circuit Response Data (NUREG/CR-6931, Volume 1)

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Publication Information

Manuscript Completed: January 2008
Date Published: April 2008

Prepared by:
S.P. Nowlen, F.J. Wyant

Sandia National Laboratories
Risk and Reliability Analysis Department 6761
P.O. Box 5800
Albuquerque, NM 87185

H. Woods, NRC Project Manager

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

NRC Job Code N6125

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Abstract

This report documents the electrical performance and fire-induced failure cable test results from the Cable Response to Live Fire Project (CAROLFIRE). CAROLFIRE testing included a series of 78 small-scale tests, and a second series of 18 intermediate-scale open burn tests. The tests were designed to complement previous testing and to address two needs; namely, to provide data supporting (1) resolution of the ‘Bin 2’ items as identified in Regulatory Issue Summary 2004-03 Revision 1 - Risk-informed Approach for Post-Fire Safe-Shutdown Circuit Inspections, and (2) improvements to fire modeling in the area of cable response to fires. The small-scale tests involved one to six lengths of cable exposed to grey-body radiant heating in a cylindrical exposure chamber called Penlight. The intermediate-scale tests involved exposure of cables in various routing conditions to open fires created by a propene (propylene) gas diffusion burner. In both test series cables were tested as individual lengths of cable, in bundles of from 3 to 12 cables, and in a limited number of tests, fully loaded electrical raceways. Cables were tested in cable trays, in conduits, and in air drop configurations. The intermediate-scale tests included exposure of cables both in the fire plume and under hot gas layer exposure conditions. A broad range of representative cable types were tested including both thermoset and thermoplastic insulated cables that are typical of the cable types and configurations currently used in U.S. nuclear power plants. All tests measured the thermal cable response using thermocouples placed both on the surface and embedded within the target cables, and electrical cable response based on two different electrical monitoring systems. This volume of the three volume project report focuses on the electrical performance measurements and results. The data are interpreted in the context of the ‘Bin 2’ items and findings relevant to the resolution of those items are presented. Volume 2 focuses on the thermal cable response data intended primarily to support the fire model improvement need area and the development of modeling approaches and correlations to reduce the uncertainty associated with predictions of fire-induced cable failure. Volume 3 was prepared by the National Institute of Standards and Technology (NIST) and documents the thermally-induced electrical failure (THIEF) model whose development was based on the CAROLFIRE test data. THIEF takes, as input, an estimate of the air temperature time history near a cable during a fire and predicts, as output, the temperature response of the cable. The time to electrical failure is then based on an assumed failure threshold temperature characteristic of the cable of interest.

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