Research On System Design And Characteristics Of Supercritical CO₂ Power Cycle Based On Lead-cooled Fast Reactor

Lead-cooled fast reactor has broad applications in the areas of distributed energy supply,nuclear propulsion,and transportable nuclear reactor power,as one of the Generation ?(Gen ?)nuclear reactor systems.Lead-cooled fast reactor has good performance in neutronics,thermal hydraulics,inherent safety features,and compact system layout.Supercritical CO2(sCO2)power cycle has compact layout,simple structure,and high thermal efficiency,its application in lead-cooled fast reactor power conversion system helps the miniaturization and modularization of the whole system.This thesis focuses on the high-efficiency energy conversion system,and conducts research on the design and thermodynamic performance analysis of the sCO2 power cycle,which is based on lead-cooled fast reactor.Firstly,the thermodynamic model of the sCO2 power cycle based on lead-cooled fast reactor was developed.Regarding the special temperature constraints of the lead-cooled fast reactor heat source on the power cycle,this thesis compared the sCO2 power cycle performances under different cycle layouts in terms of efficiency,compatibility of power cycle with heat source,and system complexity.Results show that the recompression cycle match well with the heat source.Though the recompression cycle has lower efficiency than that of the intercooling cycle,its structure is relatively simple,which is recommended at typical heat source temperatures.In addition,the measures were proposed to make the power cycle satisfy with the heat source constraints of lead-cooled fast reactor without bringing obvious effect on the efficiency,including adjusting the cycle maximum pressure,turbine inlet temperature,and split ratio.Results could provide important theoretical reference for both the selection of cycle layouts and cycle parameters.Secondly,regarding the strict requirements on the heat absorption temperature of sCO2 power cycle while the heat source temperature is low,this thesis proposed a two-circuit reheating system.Combining the usage of reheating system,the heat source temperature difference is reduced and the influence of narrow heat source temperature range on the sCO2 power cycle is avoided.What's more,a two-circuit reheating system was designed with using the printed circuit heat exchanger,which could avoid the impact of different heat capacities between main heating and reheating on the thermal stability of the reactor pool.At the same time,the intermediate circuit is removed to improve the compactness of the system.Results show that,the two-circuit reheating system is more suitable for lead-cooled fast reactors with heat source temperature less than 500?.And its system efficiency are about 1%and 2%higher than the three-circuit reheating system and the recompression system,respectively.Results could provide reference for the system design of power cycle based on the lead-cooled fast reactor while the operating temperature is low.At last,this thesis conducts research on the effects of inlet Reynolds number on the lead side and heat exchanger effectiveness on the overall system performance with using intermediate heat exchanger in different channel types.Results show that the circular straight channel(lead)-offset rectangular fin(sCO2)heat exchanger has the smallest volume,and the pressure drop has lower effect on the system efficiency.While the inlet Reynolds number is about 6000,the system efficiency and the volume of the heat exchanger could be considered at the same time,since higher inlet Reynolds number reduces the system efficiency and the opposite increases the volume of the heat exchanger.As the heat exchanger effectiveness varies,the maximum value of the system efficiency occurs,and the inlet Reynolds number impacts on the corresponding heat exchanger effectiveness of maximum system efficiency.Meanwhile,when the heat exchanger efficiency exceeds 0.95,the volume increases sharply,which is not conducive to the miniaturization.Results could provide reference for both the intermediate heat exchanger conceptual design and the selection of performance parameters in system design.