This article is about the experimental and computational research of the modernized separation part of the SPP-500-1 moisture separator--steam reheater. These devices are operating at nuclear power plants with RBMK-reactors. Modernization of the separation part of SPP-500-1 was completed by "NPO CKTI" together with the Balke-Durr company (Germany) whose stand was used for experimental studies in support of this modernization. The results of computational studies we have performed, demonstrate the efectiveness of the modernized design of SPP-500-1. The results of the computations agree quite well with the experiments, which means that the technique of two-phase low simulation adequately describes the separation process in the SPP-500-1. The proposed method of modeling two-phase low can be used for computational analysis when designing and modernizing moisture separator-steam reheaters and other heat exchangers, developed and operated at the thermal and the nuclear power plants.