Consideration of the particle behavior is essential to carry out accurately the criticality evaluation involving granular flow.. because the powder free surface deformation affects the criticality evaluation result. The conventional criticality evaluations could not consider the powder deformation. Therefore, we have developed a new code system by coupling the DEM simulation code with a continuous-energy Monte Carlo transport code to investigate the effect of the free surface deformation on the criticality evaluation. (C) 2004 Elsevier B.V. All rights reserved.