Numerical Simulation of the Motion and Solidification of Melted Fuel during a Serious Accident in a Fast Reactor

Abstract

A model was developed for the motion and solidification of melted fuel in channels for coolant passage in the end breeding zone during a serious accident with core meltdown. The model is a combination of the heat conduction and volume solidification models. It takes account of channel narrowing and the increase of the viscosity of the moving melt. The model studies the change in the thickness of the solid scale deposit in the channel and the melting depth of the channel material. The problem of the motion of the melt is solved mathematically using a hybrid method. The initial approximate analytic solution of the momentum and continuity equations is obtained by the method of reducing to an integrodifferential equation, which is then solved numerically by the Runge–Kutta method. The heat transfer problem is solved numerically by the finite-difference method. Numerical results on the penetration length of the aluminum oxide melt in quartz tubes with different diameter under the THEFIS experimental conditions are obtained; the results agree with the experimental data. The numerical results from analysis of the motion and solidification of melted fuel from a basin, formed in the reactor core after core meltdown, in the channels between the fuel elements in the bottom breeding zone and the zone of the gas cavities of the fuel elements are obtained. The effect of various parameters on the computational results is estimated.