[en] Reliability of reactor systems under seismic events is a major concern for the safety of the nuclear power plants. This paper deals with the effects of the core barrel on the seismic response of reactor tanks. The main emphases are the effects of core barrel on the free-surface wave height and the fluid coupling effects between the core barrel and primary tank. This study represents an initial step to investigate the effects of in-tank components, structures on the seismically-induced hydrodynamic behavior of the reactor tanks. To simplify the analysis, the tank used in the study is simulated by a two-dimensional model. Two parametric studies were carried out in which the wall flexibility and location of core barrel were used as parameters respectively