Abstract
As for standardization of a repair technology for nuclear reactors with a laser welding technique, a numerical study was performed to investigate precisely phase change phenomena between the solid and liquid state of micron-sized metallic particles by the laser irradiation. The metallic particles are embedded in the crack on the outer surface of nuclear components and then the laser is irradiated from the upper to them. The metallic particles melt and the crack is restored by solidifying of the melted metallic particles. This paper describes the numerical results on the phase changel phenomenon during melting and solidification of the metallic particles.