This article presents the results of an experimental and theoretical study on using a preliminary separator Powersep to improve the performance of moisture separator-steam reheaters at Kursk NPP. Modernization of SPP-500–1 was completed by «NPO CKTI» together with the German company Balke-Durr. The project of modernizing the MSR of Kursk NPP differs from the MSR modernization projects for Leningrad NPP and Smolensk NPP. The installation of a preliminary separator has led to a deterioration in the performance of the MSR. A few solutions to this problem were proposed, the best option is to install a perforated separator (perforated sheets) at the entrance to the distributing manifold separation units. Therefore, experimental studies on the effect of the preliminary separator and the perforated separator on the performance of the MSR at Kursk NPP were performed at the stand of the Balke-Durr company. The previously proposed technique for modeling two-phase flow was used during the computational research. The obtained results agree rather well with the experimental results.