Particle Method

Molten Fuel Behavior Analysis with Moving Particle Semi-implicit (MPS) Method

Moving Particle Semi-implicit (MPS) method was originally developed by S. Koshizuka and Y. Oka in 1996 as one of the fully Lagrangian particle methods. The followigns are the major characteristics and often great advantages of the method compared with Eulerian methods:
(1) No need to generate calculation meshes
(2) No need to determine interfaces explicitly
(3) No need to evaluate advection (convection) term explicitly
In our research group, we are further developing the method with a focus on applying the method to simulate core degradation and the subsequent melt (corium) behavior during a postulated severe accident of a nuclear reactor. As briefly described in the following figures, the method enables detailed evaluation of the corium behavior with complex multi-interfaces involved in the lower plenum of a reactor pressure vessel.

Recently, we have been developing the MPS method in national and international programs with great success. Our latest project addresses revealing insights to the current status of fuel debris in the pedestal region of Fukushima Daiichi Unit-3 (and Unit-2) by utilizing our developed method.