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Hazard Assessment of Fire in Electrical Cabinets

Elyahu Avidor, Francisco J. Joglar-Billoch, Frederick W. Mowrer, Mohammad Modarres

Nuclear Technology

Volume 144 / Number 3 / December 2003 / Pages 337-357


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Fire in electrical cabinets is of major concern in nuclear power plants. With the need to reduce incoming electrical power from 14 kV to as low as 50 V, and the need to supply power to hundreds of electrical components, there is an abundance of electrical cabinets in nuclear power plants. The combination of fire load and live electrical energy within electrical cabinets has caused fires and explosions. Such fires are of concern as they may disrupt the delivery of electrical power and instrumentation and control in the plant. In addition, the fire can propagate to nearby cabinets and plant components. This paper presents advances in the knowledge and understanding of the conditions inside a cabinet due to fire and ranks fire hazard potential of electrical cabinets.

Test results for electrical cabinet fires have been reported by Sandia National Laboratories and by the Technical Research Centre of Finland (VTT). The Sandia tests provide data for fires in control cabinets. The VTT tests provide a model for calculation of burning rates inside a specific electrical cabinet. This research included a site visit to a nuclear power plant to understand variations in electrical cabinet design as well as performing 39 cabinet fire tests with varying burning rates, ventilation openings, and cabinet sizes. Two types of fuels were used for this study: propane gas and heptane liquid. This paper identifies the minimum fire size that can be maintained in a cabinet as a function of ventilation openings, cabinet wall temperatures, and radiation levels, and the characteristics of external smoke and fire plumes. Based on the test results, a one-zone model was developed for mathematical simulation. The model was used to expand on the results of the tests to construct a risk matrix of fire hazards for various cabinets as a function of the cabinet size, fire size, and ventilation openings.

Since the test results in this study are based on propane and heptane as the fire load, it is desirable to also test the effect of fire load from electrical components and wiring, given a range of cabinet dimensions and vent conditions. Heat flux measurements should include the external smoke and/or flame plumes. Further studies should analyze the possibility and implications of an explosion within a cabinet, and results should be compared with existing national and international design standard requirements.

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