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In the VVER -TOI project, new layout solutions were applied in the reactor plant as part of which the steam removal system from the steam generator was changed. Namely, in contrast to the VVER-1000 and VVER-1200 where the steam removal was organized through ten nozzles combined into a steam collector, in the VVER -TOI SG the steam removal was arranged through one nozzle located on the cold collector side. This change leads to the formation of a non-uniform velocity field in the separation volume. To ensure the steam separation characteristics of a horizontal steam generator with one steam nozzle, it was proposed to create a non-uniform resistance on the way of steam motion from the evaporation surface into steam nozzle applying a non-uniform degree of the distribution perforated plate (DPP) perforation. Two computer models of the SG steam volume with different steam removal schemes (one and ten nozzles) were developed, a set of studies on verification and validation was carried out and a set of calculations were performed. Further, to determine the non-uniform degree of DPP perforation, a set of optimization calculations of the SG steam volume with one steam removal nozzle was performed. The non-uniform degree of DPP perforation of the VVER-TOI SG was selected, which provide steam velocity distribution as close as possible to SG with ten steam nozzles. To justify the chosen design, sensitivity analysis was also carried out according to the hole diameters tolerance and steam load profile.

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