The flood safety of the Nuclear Power plant KKG in terms of dam breaks scenarios at the River Aare was investigated through using a deterministic method. Based on the requirements of the Swiss Federal Nuclear Safety Inspectorate (ENSI), four dam break scenarios were identified for the investigation. The scenarios were based on conservative assumptions of different combinations of weirs' breaks. The propagation of the flood waves were computed by means a hybrid model as a combination of one (1D) and two-dimensional (2D) models. Based on the simulations it was possible to estimate the risk of flooding of the KKG area and if needed to suggest some measures to prevent such flooding. Additionally it has been investigated, if important water intakes were at the risk in regard to the allowable maximum and minimum water level. The sediment transport was studied qualitatively, if there were high erosion risks. According to the calculated bottom shear stresses the river bed erosion is possible only locally and over a very short time period.