Pressure surges occurring in pipeline systems may be caused by fast control actions, start-up and shut-down processes and operation failure, as well as flow rate fluctuation. They lead to water hammer upstream the closing valve and cavitational hammer downstream the valve, which may cause considerable damages to the pipeline and the support structures. Appearance of water hammer in thermal-hydraulic systems was widely studied employing different stateof-the-art thermal-hydraulic codes. Before carrying out the water hammer analysis, it is very important to match the model and to perform the analysis of its sensitivity. The paper presents an analysis of the water hammer experimental test performed at the Fraunhofer Institute for Environmental, Safety and Energy Technology (UMSICHT) using the RELAP5/Mod3.3 thermal hydraulic code. The model sensitivity study was performed by using the Fourier amplitude sensitivity test (FAST) method. The FAST method aims to determine the most important input parameters that are major contributors to the model output uncertainty. Such information can be used further for a more detailed system study and development of improvements or preventive actions.

Keywords: water hammer, UMSICHT, RELAP5 model, sensitivity analysis, FAST