Due to increasing share of electricity in final energy consumption, the capacity of the global nuclear energy must be expanded. This will enable defossilization of the primary sector and stabilize the entire power system. Capacity increase can be achieved by constructing new nuclear power plants, but from an economic perspective, extending the operational lifetime of existing plants is also very important. This thesis focuses on the blowdown system, which reduces wear on steam generators in pressurized water reactors and extends their operational life. We examined potential damage to piping and support structures during operation. A hydraulic model was developed, based on the actual geometry of the pipeline. It includes local pressure losses occuring at flow path geometry transitions. A model of the critical valve closure was implemented, and the system response to different closure times was analyzed. A potential location for water hammer was identified. Thermodynamic variables were monitored and evaluated to characterize the transient phenomena. We found that longer valve closure times result in smaller pressure surges due to gradual changes in flow resistance. In contrast, rapid valve closure may create local conditions for two-phase flow and potentially trigger water hammer in the system.
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