United States Nuclear Regulatory Commission - Protecting People and the Environment

Circuit Bridging of Components by Smoke (NUREG/CR-6476, SAND96-2633)

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Publication Information

Manuscript Completed: October 1996
Date Published: October 1996

Prepared by:
T.J. Tanaka, S.P. Nowlen, D.J. Anderson
Sandia National Laboratories
Albuquerque, New Mexico 87185-0747
Operated by Sandia Corporation

C. Antonescu, NRC Project Manager

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

NRC Job Code W6051

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Abstract

Smoke can adversely affect digital electronics; in the short term, it can lead to circuit bridging and in the long term to corrosion of metal parts. This report is a summary of the work to date and component-level tests by Sandia National Laboratories for the Nuclear Regulatory Commission to determine the impact of smoke on digital instrumentation and control equipment. The component tests focused on short-term effects such as circuit bridging in typical components and the factors that can influence how much the smoke will affect them. These factors include the component technology and packaging, physical board protection, and environmental conditions such as the amount of smoke, temperature of burn, and humidity level. The likelihood of circuit bridging was tested by measuring leakage currents and converting those currents to resistance in ohms. Hermetically sealed ceramic packages were more resistant to smoke than plastic packages. Coating the boards with an acrylic spray provided some protection against circuit bridging. The smoke generation factors that affect the resistance the most are humidity, fuel level, and burn temperature. The use of CO2 as a fire suppressant, the presence of galvanic metal, and the presence of PVC did not significantly affect the outcome of these results.

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