Analyzing the Thermal Characteristics of a Small Capacity NPP Thermal Power Circuit with Nonaqueous Working Fluids

Predesign assessment of prospects for developing small capacity nuclear power plant (SCNPP) thermal power circuits operating with various nonaqueous working fluids is given. The article presents the results obtained from an analysis of makeup versions of the SCNPP secondary (turbine) circuit, the primary circuit of which is an autonomous microfuel molten salt cooled reactor (MARS). The thermal process schemes of an open-loop air gas turbine unit without regeneration, a gas turbine unit with two-stage air compression in a compressor and regeneration, and a fluorocarbon turbine unit that uses octafluoropropane (C₃F₈) as working fluid and operates according to the organic Rankine cycle are considered. The possibility of reaching the highest thermodynamic efficiency of thermal energy conversion on the basis of a fluorocarbone turbine unit (FTU) that uses octafluoropropane as working fluid at temperatures up to 650°C is shown. The design cycle efficiency of such a unit exceeds 50%, whereas that of a gas turbine unit (GTU) without regeneration is no more than 33%. The main thermal, mass, and dimensional characteristics of the SCNPP thermal power circuit equipment for the proposed makeup versions are compared with one another. It has been found that the main technical problem faced in designing and introducing the thermal power equipment of the GTU-based secondary circuit will be the mass and dimension characteristics of the reactor core heat exchanger and the air-to-air regenerator in view of low heat-transfer coefficients. It is shown that the use of octafluoropropane as the turbine circuit’s working fluid will make it possible to design the main apparatuses with essentially more compact mass and dimension characteristics and, hence, to decrease the hydraulic losses in them and reduce their cost. The obtained results testify that mass of regenerative apparatuses operating on octafluoropropane can be decreased in comparison with that of their air-cooled analogs by up to 15 times. Based on the obtained analysis results, a list of first-priority technical problems has been formulated, the solution of which will make it possible to successfully develop the SCNPP thermal power circuit.