Development of margin assessment methodology of decay heat removal function against external hazards, 3; Forest fire hazard assessment methodology

Okano, Yasushi; Yamano, Hidemasa   

The forest fire hazard assessment methodology, which is subject to an external hazard probabilistic risk assessment, is being developed for Sodium cooled Fast Reactor in order to quantitatively evaluate frequency and consequence of a forest fire that has a potential impact on a NPP and to obtain the core damage frequency. The new methodology consists of two parts; the first one is hazard frequency-consequence domain and the second one is Level 1 PRA. This paper focuses on forest fire propagation simulations in the first part of the methodology. The simulation is utilized to evaluate intensities of the challenges by a forest fire, and sensibility studies were performed on weather conditions. Forest fire propagation simulations were performed using FARSITE code, and the results show that the key outcome parameters depend much on wind speed and humidity but less on temperature. The fire arrival time to the site is shortened around 1/5 with changing wind speed condition from the recorded highest to the condition without wind. The time is prolonged around 3.4 times with the most humid to the recorded lowest conditions, although it is changed little when varying ambient temperature from recorded-highest to the lowest. A loss of offsite power due to fireline passage across through external power lines is a potential subsequent event, and the lag time of the fire arrival to the site after the loss of offsite power was evaluated.