Particle precipitation and mixing simulated by rigid dynamic-moving particle semi-implicit (RD-MPS) method

The particle precipitation and mixing related to the corium debris bed formation and coolability in severe accidents are investigated by using a new CFD tool, called the ADDA code. The code is developed based on an enhanced particle method which combines the MPS (Moving Particle Semi-implicit) algorithm with the rigid body dynamics method. The analysis successively simulates the entire process of debris bed formation which includes corium jet breakup, mixing, and sedimentation to identify the key characteristics to form the corium debris bed with coolable configurations. The 2-D and 3-D simulation re-created the detailed flow structures and mixing phenomena and final sedimentation process. For the analysis of the debris formation, it is suggested that the full 3-D simulation provides more accurate prediction than ones from the 2-D simulations since the debris formation largely depends on the process of particle precipitation and mixing phenomena prior to its settlement. (author)