Engineering solutions and process methods to increase the efficiency of moisture separator-reheaters being an equipment part of NPPs with VVER-1000 and VVER-1200

The article considers the designs of heat-exchanging cartridges of moisture separator-reheaters (MSRs) of increased efficiency being a part of the equipment of NPPs with VVER-1000 and VVER-1200. One of the main problems of NPP saturated steam turbines is the reduced moisture content in the turbine flow part and the deficiency in the heating steam temperature resulting in the need to modify the existing designs of moisture separator-reheaters and increase their heat transfer. Some proposed engineering solutions and process methods for improving the efficiency of heat-exchangers lie in increasing the heat transfer surfaces using a more branched surface of heat-exchanging tubes. Such designs are heat-exchanging cartridges of reheaters, consisting of a large number of heat-exchanging tubes with six and eight longitudinal U-fins, MSR designs SPP-1000 and SPP-1200, respectively. It is noted that cartridges with six longitudinal U-fins do not provide the heating steam temperature deficiency of 6 °C for more powerful facilities of NPP Power Units with VVER-1200. An appropriate engineering solution for meeting this requirement is the application of heat-exchanging tubes with eight longitudinal U-fins in the cartridges. The article contains advantages and disadvantages of the considered design of longitudinally finned tubes. The main disadvantages of tubes with eight U-fins are the increased metal consumption per heat-exchanging cartridges and the lack of conditions for large-scale production of tubes of such class. We considered the engineering solution to apply the reheater heat-exchanging cartridges with low-profile monometallic tubes, allowing keeping the modular principle of construction of all units in previously existing designs. The article states approaches to the selection of heat-exchanging tube blanks subject to the range of products manufactured by global and domestic manufacturers. Some results of studies of the structure and physical and mechanical properties of the heat-exchanging tubes are shown for optimal selection of heat-exchanging tubes for MSR SPP-1200. It is noted that the feasibility of the proposed engineering solutions for modification of MSRs should be supported by the results of thermal and hydraulic calculations as well as a comparison of the technical characteristics of the designs before and after the modification.