Abstract
The secondary system pipe rupture occurred on August 9,2004, at Mihama nuclear power plant unit 3. Eleven workers, who were preparing for an annual outage that was to start from August 14^<th>, suffered burn injuries, of who five died. Pipe wall thinning was occurred by erosion corrosion. We experimented and analyzed the mechanism to damage. The results show that the ruptured pipe have the turning fluid and the unstable flow. However, the thinning speed and the rupture stress are in the normal range. We guess that the turning fluid and the unstable flow are only a characteristic generated by the piping construction.
