Prediction of SG Tube Support Plate Flow Area Blockage Rate Using SG Wide Range Level Measurements and Hydrodynamic Analysis

摘要

Some nuclear power plants have recently experienced hydrodynamic instability in steam generators (SGs). Instability, if present in the SG of a pressurized water reactor, results in the periodic oscillation of the water level, steam flow, feedwater flow, arid the flow through the circulation loop. In this instability analysis, the major parameters are the power level and flow area of the tube support plate (TSP). The threshold power above which instability may occur is generated by variations in TSP flow area. The current method of estimating the blockage rate is the visual inspection of the SG interior. This type of visual inspection, however, requires many resources. To improve this method, we focus on measurements of the SG level. The measurements of the level change because the SG downcomer flow rate varies due to the blockage of the TSP flow area. To quantify this effect, we calculate the circulation ratio in relation to changes in TSP flow area. In addition, we evaluate the pressure drops that affect the SG water level. Sensor drift analyses of the level measurements are performed to confirm that the level variance is derived from system characteristics rather than sensor drift. Finally, the blockage rates of the TSP flow area are generated by using measurements of the SG water level.