For nuclear power plants, the four major requirements are 1) high safety, 2) high reliability, 3) good economical acceptability, and 4) as few as possible environmental impact. However, it is still difficult to completely avoid problems for structural materials as structural stress corrosion cracking (SCC) and for piping systems as flow accelerated corrosion (FAC), liquid drop impulsion erosion (LDI). Especially FAC and LDI are uncertainty phenomenon as pipe wall thinning, so there is the piping rupture accident risk on all of piping systems under the specific conditions. In Japan, after in August 2004, the accident of the secondary pipe rupture in Mihama Power Plant Unit 3, The Kansai Electric Power Co., Inc. (KEPCO), R&D projects about pipe wall thinning phenomenon and mechanism had been promoted in many organizations. The other hand it is requested to evaluate the safety and reliability of piping systems of long term operating plant and with on special case of seismic condition. It was requested to be able to evaluate pipe wall thinning and its reliability with more accurate. This project had programmed under the government budget from 2006 planed until 2010 fiscal year [1]. At the mile stone of half span, the project had these fruits, 1) Computer program for FAC simulation, 2) Droplet phenomena for LDI simulation, 3) Simplified calculation model of pipe wall thinning for seismic evaluation.

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