Development of a hazard curve evaluation method for a forest fire as an external hazard

Okano, Yasushi; Yamano, Hidemasa   

An external hazard curve of a forest fire is evaluated based on a logic tree. The logic tree consists domains of "forest fire breakout and spread conditions", "weather condition" and "vegetation and topographical conditions". A location nearby a typical nuclear power plant site in Japan was selected, and the frequency of a large forest fire of the location is approximately 1/5 of the average in Japan. Forest fire breakout points were selected considering typical forest fire causes in Japan. The weather conditions are represented by two parameter sets of "temperature-humidity" and "wind direction-wind speed". A number of forest fire simulations were performed to obtain a response surface for a frontal fireline intensity. The hazard curve is therefore evaluated by a Monte Carlo simulation such that the annual exceedance probability is about 1.010 per year for the frontal fireline intensity of 200 kW/m and about 1.310 per year for 300 kW/m.