Numerical investigation of multi-dimensional characteristics in sodium combustion

Abstract

Multi-dimensional sodium combustion behavior has been numerically investigated in the present paper. A new computer code AQUA-SF has been developed for this purpose. The code includes two sodium combustion models (so called ‘spray combustion’ and ‘pool combustion’), a mass and heat transfer model considering a six-flux gas radiation and a coagulation and sedimentation model of sodium oxide and hydroxide aerosols. The sodium spray combustion rate is evaluated by a summation of the combustion rate of each sodium droplet with an individual diameter. A flame sheet model is applied to situations where sodium spreads out on the floor and a pool combustion takes place. The model assumes an infinitely thin flame above the pool surface and is based on a mass and energy balance in the flame. As the results of numerical analyses of a sodium spray combustion test, a location of high-temperature core region and a maximum temperature agrees with the experiment. Good agreements of an overall transient behavior are obtained in a large-scale sodium combustion test analysis. The numerical analyses also demonstrate that the distributions of temperature and chemical species concentration vary with sodium combustion modes. If sodium scatters and the spray combustion is dominant, the distributions vary in space. When a large amount of sodium exists on a floor and the pool area is enlarged, the distributions are more uniform in space.