This thesis is about feedwater control in the nuclear reactor Ringhals 4, for which a power uprate is planned. With the current control strategy at high reactor power, the water level of the steam generators is controlled by feedwater ow control valves over which there is a dierential pressure of 8 bar during normal operation. If this dierential pressure can be decreased, the workload of the feedwater pumps can be reduced.
An existing Dymola model of the feedwater control system was extended and validated against data from measurements performed in the plant. The validations showed that the model is accurate enough to use, but margin is needed when drawing conclusions. Studies using the validated model were carried out to see if it is possible to use the high power control strategy at low reactor power, how the feedwater control works at uprated power level, if it is possible to decrease the dierential pressure over the control valves, and if it is possible to leave the control valves fully open and use only the feedwater pumps to control the steam generator level. The results indicate that the feedwater control is satisfactory in all four studied cases. However, more thorough investigations are needed before drawing any nal conclusions.