Study of Electrical Malfunctions as a Function of Ambient Temperature and Carbon Particle Concentration

The malfunction of electrical equipment exposed to fire smokes is a major issue in nuclear facilities safety assessments. For over 15 years, the ASNR has been carrying out studies to provide data on electrical malfunctions obtained from reference equipment. Thus, ASNR decided to perform an analytical study to explore the malfunction phenomenon, and to understand how far the soot contained in the smoke promotes electrical malfunctions. An analytical device (called DANAIDES) was specifically designed to expose supplied electrical equipment to a thermal stress and/or a mass concentration of soot (in steady state). First, the experimental protocol plans to study the effect of soot on electrical malfunctions caused by the heating of the components. In a second step, the equipment is confronted to another malfunction type caused by electrical leakage currents through carbon bridges due to the soot deposit. After showing that the presence of soot clearly shortens the thermal malfunctions time, since the thermal stress around the equipment is sufficient, the study was also able to highlight that soot caused leakage current malfunctions, from temperatures significantly below the heat stress threshold. This study highlighted the fundamental role of carbon aerosols in the occurrence of electrical malfunctions. This is a first step towards possibly taking the presence of soot into account in safety criteria, which to date are only based on a temperature threshold. However, to define a reliable malfunction criterion based on a critical soot threshold, a similar study should be conducted with real fire soot, so that the results can be considered generalizable and representative of real fire scenarios.