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FDS (Fire Dynamics Simulator) is the software to computing fluid dynamics which taking the flowing in fire as the main simulation target. In this paper, a model closed to real fire scenario of UBS (emergency diesel generator) fuel tank room of NPP is established by FDS. By analyzing this model, details on the effectiveness of controlling the fire source heat release rate, the key point temperature and the slices in the process of fire extinction based on sprinkler systems are discussed. In addition, it will show the advantages and feasibilities of FDS in NPP(nuclear power plant) application.

UBS fuel tank rooms of NPP are the places which are suffer from high frequency of fire accidents and when the fire accident occurred, it would be hard to controlled put out. High radiation made by the swift and violent fire which do harm to equipments and tanks nearby may expand the fire disaster. On the other hand, if the fire in fuel tank room touched operation functional area in NPP, the condition of reactor will be changed, as well as increasing the risk of the safety of nuclear.Based on this discussion, study on fire hazard in UBS fuel tank rooms is an important subject in NPP fire protection.In China, studies on fire in UBS fuel tank room of NPP are relatively late, while methods and technology are backward.The second generation improved nuclear power project, which is mainly being used in China, is using a set of manual calculation methods introduced by France. The method is based on normalized thermal program. This program can get the time of the fire lasting in fire district by calculating fire load densities, and then compare with fire resistance of boundary, which cannot get the actual situation of temperature rise in fire and describe the control effect of sprinkle system. Consequently, there are some limitations in this method and technology [1]. In this study, a model closed to real fire scenario of UBS Fuel Tank Room is established in NPP, and details on the effectiveness of controlling the fire source heat release rate, the key point temperature and the slices in the process of fire extinction based on sprinkler systems are discussed. In addition, it will show the advantages and feasibilities of FDS in NPP application.

This work based on the FDS has established a set of close to true fire scenario of UBS fuel tank room of NPP, and studied the control effect for fire in different distances and different sprinkler pressures. Simulation results indicate that when the sprinkler system pressure release for 1 bar, spacing for 2.0 m and 3.0 m, the sprinkler system can have a cooling effect on fire, which reducing the heat release rate to effectively controlling the fire and better for fire control with the sprinkler spacing of the reduction of the sprinkler system. In particular sprinkler spacing, increasing the release pressure can get more droplets kinetic energy and more effectively to fire the surface to reduce the ignition heat release rate. From the change of temperature for point A to get the result that in the droplets coverage of the area, the temperature is reduced when the droplets get through the layer, at the same time the effects of sprinkler pressure is no longer apparent.From the change of temperature for point B, it can be noticed that the smoke rise to the ceiling is affected by the ceiling jet, and increasing the pressure of the sprinkler release if the position is away from the fire source to make the droplets through the smoke layer and get cool. It is seen from the slices of different sprinkler pressure at 65s that the temperature above the fire source is reduced with the opening of the sprinkler system. It is effect to the temperature weakening by sprinkler system within coverage area. Based on the particularity of the structure of NPP, it is difficult to do an entity experiment on the researching on the fire in NPP fuel tanks rooms. According to the real environment situation of the scene, relatively credible fire load and the model of the distribution for the fire source were set up. By FDS simulation, it’s able to calculate the real situation of the fire temperature rising, as well to describe the effect of sprinkler system in controlling the fire. From the point of nuclear safety review, the way of fire evaluation will be changed, and more useful references for NPP fire protection will be provided by FDS.