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Fire-induced failure mode testing for dc-powered control circuits

Nowlen, Steven P.; Taylor, Gabriel; Brown, Jason

The U.S. Nuclear Regulatory Commission, in concert with industry, continues to explore the effects of fire on electrical cable and control circuit performance. The latest efforts, which are currently underway, are exploring issues related to fire-induced cable failure modes and effects for direct current (dc) powered electrical control circuits. An extensive series of small and intermediate scale fire tests has been performed. Each test induced electrical failure in copper conductor cables of various types typical of those used by the U.S. commercial nuclear power industry. The cables in each test were connected to one of several surrogate dc control circuits designed to monitor and detect cable electrical failure modes and effects. The tested dc control circuits included two sets of reversing dc motor starters typical of those used in motor-operated valve (MOV) circuits, two small solenoid-operated valves (SOV), one intermediate size (1-inch (25.4mm) diameter) SOV, a very large direct-acting valve coil, and a switchgear/breaker unit. Also included was a specialized test circuit designed specifically to monitor for electrical shorts between two cables (inter-cable shorting). Each of these circuits was powered from a nominal 125V battery bank comprised of 60 individual battery cells (nominal 2V lead-acid type cells with plates made from a lead-cadmium alloy). The total available short circuit current at the terminals of the battery bank was estimated at 13,000A. All of the planned tests have been completed with the data analysis and reporting currently being completed. This paper will briefly describe the test program, some of the preliminary test insights, and planned follow-on activities.