Horizontal Steam Generators: Design Improvement and Experimental-and-Computational Studies (Review)

A review is presented of designs of horizontal steam generators (SG) for nuclear power plants (NPP) with water-moderated water-cooled reactors (VVERs) and of experimental-and-computational studies of thermohydraulic processes running in them. Horizontal SGs are examined from the first commercial design of the PGV-440 SG and the most widely used today PGV-1000M SG to the steam generators developed for the new generation reactor units of types VVER-1200 and VVER-TOI as well as for the high-power VVER-1500 reactor. A comparative analysis was carried out of the experimental facilities developed for the investigation of thermohydraulic processes occurring in a horizontal steam generator. Each of the examined experimental facilities has limitation related to the capabilities for the simulation of a full-scale SG caused by either geometric characteristics or thermohydraulic conditions. Nevertheless, it has been demonstrated that we have at present a sufficiently large experimental database suitable for validating computational codes simulating thermohydraulic characteristics of a horizontal steam generator. A review of the available computational codes is presented. The STEG code in which the two-phase flow is described by multifluid models is examined in more detail. The validation of the STEG code against experimental data on void fraction, pressure drop, and water velocity demonstrated high accuracy of the predictions. One of the problems to be solved in designing horizontal steam generators for new generation reactor units is the improvement of the equalization ability of the submerged and steam-receiving perforated sheets due to the enhanced nonuniformity of the steam load on the evaporation surface and of the steam flow in the steam space. The results are presented of the experimental-and-computational investigation of the equalization ability of perforated sheets, which corroborate the possibility of its improvement by application of a variable perforation ratio. The areas of further experimental investigations into thermohydraulic processes in a horizontal steam generator and ideas for improving the computational codes are formulated.