Today, the world attaches great importance to the development of low-power nuclear power plants (NPPs). Ukraine with a large machine-building potential should take its rightful place among the manufacturers of equipment necessary for AIPS. One of the main elements of a reactor plant (RP) is a steam generator (SG).
The paper analyzes the state of development of low-power NPPs, existing structures of SGs. From the analysis of the used SG designs, it was concluded that the most acceptable is the SG with coaxial coils. Titanium alloys are used as the material for the heat exchange tubes. A vertical steam generator with steam superheating used in the KLT-40S NPP was chosen as a prototype of the design. The proposed design of SG does not have the drawbacks of direct-flow SG and allows for blowing, which greatly simplifies the water-chemical regime. A computational comparison of different schemes of steam turbine plants was carried out, which showed an increase in the absolute electrical efficiency with a complication of the thermal scheme due to the use of regenerative heaters, an intermediate separator and a steam superheater. It is shown that each measure leads to an increase in efficiency by about 1%.
The technique of technical and economic calculation of SG has been developed. To optimize according to the criterion of the minimum of the reduced costs, it is necessary to determine the cost of the SG and the energy consumption for the circulation of the coolant and the working fluid through it. To determine the cost, a structural calculation of the SG has been developed, namely, the dimensions of its main elements: heat exchange tubes (HET), cylindrical part, cover, bottom and housing branch pipe. It is shown that the design under consideration has certain features, namely, to determine the main dimensions, it is necessary to set five parameters, instead of four for the rest of the heat exchangers: the HET diameter, the HET positioning step in the vertical and horizontal directions, the feed water velocity in the HET and the coolant velocity in the annular space. The last parameter determines the number of rows of concentric coils that make up the heat transfer area.
When developing an algorithm for thermal calculation, various formulas for determining the heat transfer coefficients were analyzed for the transverse flow of the coolant around horizontal coils and for the flow of the working fluid in the heat exchange tubes at five heat transfer sections. Variant calculations were carried out to determine the influence of the main design parameters on the SG heat exchange area. A method has been developed for the hydraulic calculation of the heat-exchange surface and areas before and after the heat-exchange surface in the SG. Variant calculations have been made to determine the effect of design parameters on the hydraulic resistance of the steam generator. The conditions that ensure the hydraulic stability of the operation of a once-through steam generator (OTSG) have been investigated. The analysis of the mathematical model that explains the occurrence of hydraulic instability in a channel with a two-phase working fluid is carried out. A physical explanation is made for the use of a throttling washer in the inlet section to prevent instability from occurring. It is shown that additional resistance can be provided by certain dimensions of the feed tube supplying water to the HET. As a result of the analysis of the conditions for achieving hydraulic stability, an insufficient certainty of this inequality was revealed. It is proposed to determine the additional resistance, taking into account the possible deviation of the dimensions of the HETs, which among the considered parameters most affect the calculated hydraulic resistance of the HET. Optimization of the main design parameters of the OTSG was carried out. When calculating the cost of the SG, the costs of welding HET were taken into account. This made it possible to determine the optimal diameter of the HET based on the minimum of the reduced costs. The optimal speed of the feed water at the inlet to the HET is 0.71 m / s. It was determined that the thickness of the annular gap between the casing and the shaft for the passage of the coolant is determined from the condition of the minimum hydraulic resistance when the coolant leaves the nozzle.
