In this paper, investigations of the safety of electrical cables in nuclear plant fire were described by CFD analysis and by flammability tests of power and control cables. For CFD analysis, thermal configurations of a nuclear power plant room in a fire accident was calculated by the Fire Dynamics Simulator (FDS). For flammability tests of cables, the cone-calorimeter test machine was modified to use the cable tray type specimen. The modified cone-calorimeter test machine is able to test the flammability of cables and insulation resistance from room temperature to 800°C.

In the flammability test, electric power and control cables of the polyethylene sheathed cables which had been applied to the nuclear plants were adopt.

The cable specimens of which length were 600mm, were fixed on a cable tray specimen. The temperature of the cable specimens was raised to from 200 to 570°C using the cone-type electrical heater. During the tests, electrical resistance and temperature was measured to evaluate safety of insulation resistance of cables.

As results, the destruction of the insulation resistance of a polyethylene sheathed control cable was observed in the examinations, temperatures of which were 400°C and 500°C.

In the numerical simulation using Fire Dynamics Simulator (FDS), an electrical switchgear room in nuclear plants was supposed as an evaluation model. As the fire source, fire in motor control cabinet in the switchgear room on nearby cable tray was applied to CFD analysis. From the results of numerical simulations, the heat configuration and temperature in the switchgear room was evaluated and radiation heat from fire to the cable trays was calculated.

Considering these results given by flammability tests of electrical cables and CFD analysis, the safety of a switchgear room in nuclear plants was shown.

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