Izvestia Vysshikh Uchebnykh Zawedeniy. Yadernaya Energetika

The peer-reviewed scientific and technology journal. ISSN: 0204-3327

Vertical steam generators for VVER NPPs

9/20/2018 2018 - #03 Thermal physics and thermal hydraulics

Egorov M.Yu.

DOI: https://doi.org/10.26583/npe.2018.3.08

UDC: 621.039

Steam generators for NPPs are the important large-sized metal consuming equipment of nuclear power installations. Efficiency of steam generator operation determines the overall service life of the whole nuclear facility.

The main aim of the current study is to analyze the advantages and shortcomings of horizontal and vertical types of steam generator design. This analysis is aimed at the definition of recommendations for the development of advanced steam generators for perspective Russian units of NPPs with VVER reactors of increased power.

Design solutions and fifty-year experience of operation of 400 steam generators of horizontal type accepted in Russia and of vertical type applied by Westinghouse, Combustion Engineering, Siemens, Mitsubishi, Doosan were analyzed within the framework of this study. Advantages and drawbacks of both types of devices determining the development of conditions of the operating processes were also identified and systematized.

Currently NPPs equipped with VVER are characterized with extended surface area of containment shells due to the application of four-loop design configuration and horizontal-type steam generators. It was established that steam generator equipment of horizontal type is characterized by such inherent disadvantages of design, technological and operational character as the following: 1) small height and volume of the vapor space above the evaporation surface reducing separation capabilities and power of the equipment as a whole; 2) impossibility of organizing separate single-phase pre-boiling section. As the result, horizontal steam generators with dimensions permissible for railroad transportation and, for VVER-1200 with vessel diameter equal to 5 m by water transport as well, have exhausted the possibilities for further significant increase of the per unit electric power.

The demonstrated advantages of vertical-type steam generators were as follows: 1) absence of stagnant zones in the second circuit, and, consequently, of hold-ups in them; 2) uniformity of heat absorption efficiency of the heating surface ensuring, as well, improved conditions for moisture separation; 3) high degree of moisture removal from steam-water mixture due to the combination of moisture separating elements of chevron and swirl-vane types; 4) increased temperature drop with parameters of generated steam elevated of by 0.3 – 0.4 MPa.

Conclusion was made on the advisability of introduction of steam generators with vertical-type layout in the Russian nuclear power generation. Practical tasks that need to be addressed in order to ensure introduction of vertical steam generators at NPPs with high-power VVER reactors were formulated.

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vertical type steam generator horizontal type steam generator light water reactor type natural circulation variable thermocyclic stress pre-boiling section heat exchanger steam-water mixture temperature difference separators of chevron and swirl-vane type containment the four-loop layout