Experimental investigations of the flow patterns in the hot leg of a pressurized water reactor

For the simulation of loss of coolant accidents in nuclear power plants, the flow patterns are predicted by using experimental results from small sized plants which usually have been achieved for fully developed flows. Experimental investigations in a large sized plant have indicated that these flow pattern maps are not fully applicable to the specific geometric properties of nuclear power plants. Therefore, we have conducted experimental investigations for cocurrent two-phase flow in the hot leg. For the experimental investigations a large sized experimental set-up has been constructed, which represents the hot leg of a pressurized water reactor at the scale of 1:1.7. To distinguish between the influence of the size of the plant and the influence of the elbow and the steam generator simulator on the flow pattern, the experimental investigations have been conducted in two steps. First, the flow in the horizontal part of the hot leg has been investigated without connecting the elbow to the plant. The flow regimes have been detected by visual observation. The experimental results are compared to those obtained for smaller pipe diameters and longer pipe lengths. Second, the 50 upwards inclined elbow and the steam generator simulator are added to the horizontal pipe and their influence on the flow patterns is investigated. (orig.)