Study on aerosol behaviors in sodium pool fire. Development of chemical reaction model and evaluation of aerosol transport

Since the sodium leakage event from the secondary loop in Monju December 1995, attention has been called upon to the mechanisms of aerosol generation and transport. In particular it is considered important to determine the fractions of the aerosol that is transported into the atmosphere and onto the sodium pool surface, because they are important parameters in evaluating the sodium fire and the floor temperature. In order to estimate the fractions, the flame structure such as the velocity, the density of chemical species and the temperature distributions must be analyzed. In an initial attempt, we have assumed the system in which the steady-state natural convection is generated by the fire in the compartment. It is also assumed that sodium-oxygen reactions are controlled by an instantaneous chemical equilibrium and the aerosols transport is due to a sum of the drag force, the thermal force and the gravity. Finally we solve the boundary layer equations for the mass, momentum, chemical species, and energy based on the theory of the laminar diffusion flame which has been studied well. From these results, it is estimated that the calculation results for burning rate are in good agreement with the experimental results. The release fraction of around 0.3, which is used in the conventional calculation, is adequate for the pool temperature of about 1000 K. To develop the models of the sodium fire on the floor and the aerosols transport is performed by Tokyo Institute of Technology (TIT), and that of the chemical equilibrium is by Japan Nuclear Cycle Development Institute (JNC). (author)