Computational Analysis for Predicting Wall Thinning Location of BWR Orifice Downstream Piping

To increase load factor of nuclear power plants, it is necessary to decrease the number of days needed for periodic inspection and the number of days of unplanned outages. One of the countermeasures for these issues is to establish a prediction method for pipe wall thinning. There are two phenomena to be considered in pipe wall thinning. They are flow accelerated corrosion (FAC) and liquid droplet impingement erosion (LDI). In boiling water reactors (BWRs), LDI tends to influence pipe wall thinning more than FAC does. LDI is the wall thinning phenomena caused by droplet impingement. It is necessary to develop an appropriate method to predict the location of wall thinning. In this paper we compared measured data with computational analysis results for the location of wall thinning. By defining that the droplet frequency distribution had double peaks at the extrapolated location from the wall of an orifice toward downstream, we were able to predict the central location of the large reduction in thickness with a difference of less than about 0.2D[mm](D: pipe diameter) from the measured location in the flow direction at the elbow.