Evaluating Nuclear Energy Power Conversion Cycles for Microreactors

Abstract

Microreactors have become increasingly popular in the past decade, but the economics of these technologies has yet to be proven. Analysis is required to support the development of microreactor designs by comparing design choices and predicting costs. A simulation tool was developed which estimates the size and cost of heat exchangers along with the efficiency of three simple power conversion cycles. Printed circuit heat exchangers with semi-circular channels were used in analysis due to their high power densities and low costs, making them extremely suitable for use with microreactors. A stepwise linear solver was implemented for steam generator analysis, while other heat exchangers use the LMTD difference method to compute overall heat transfer area. Heat exchanger analysis tool iterates on channel length to achieve convergence with user-given inputs, before calculating heat exchanger volume and cost. Cycle efficiency calculations are performed using ideal gas relationships for air and enthalpy relationships given turbine and pump efficiencies for water and CO2. An additional capability is included which can estimate the effect of a regenerative heat exchanger in the conversion cycle. A reference design was picked to show the ability of the analysis tool to effectively compare different primary fluids coupled to a steam Rankine, air Brayton, or supercritical CO2 cycle. A sensitivity study on channel diameter was conducted, illustrating the design optimization capability of the tool.