Engineering Design of High-Efficiency Multi-Purpose Nuclear Electric Power Systems

Abstract

This research focuses on analysis of power conversion system Modular Optimal Brayton Island System (MOBIS) for versatile purposes. The system adopts a supercritical CO2 (S-CO2) as working fluid to get benefit in term of thermal efficiency from its thermodynamic property characteristics. Design of MOBIS is basically based on Battery Omnibus Reactor Initiative System (BORIS) being developed at the Seoul National University as a multipurpose integral fast reactor, as the powering reactor. In addition to key components such as heat exchangers and turbomachinery, the piping system is taken into account to obtain more reasonable result in this study. Without taking any turbine valves into analysis consideration, a thermal efficiency of 42.50% can be attained. Moreover, due to its imperative role on regulating output power, the turbine valve is further studied as well to improve the system performance. Unfortunately, however, the valve has inherently nonlinearity characteristic. First of all, a combined stop valve and control valve is introduced to replace the roles of the conventional separated one. The combined valve flow coefficient data were newly generated by the Combined Airflow Regulation Analysis (CARA) and Combined Airflow Regulation Operation (CARO) experiment. Based on the CARA/CARO outcome, the cycle efficiencies were investigated for both the S-CO2 recompressing Brayton cycle and common steam turbine system as well. By adopting the combined valve, the thermal efficiency can be improved by 0.43% and 1.27% in S-CO2 recompressing Brayton cycle and steam turbine system, respectively. The improvement will be much more significant in the higher power applications. Engineering analysis is also made of the compensation of nonlinear valve characteristic. As a standard analysis code in nuclear engineering, the MARS code is utilized for the analysis to obtain more accurate results from the thermalhydraulic point of view without sacrificing the control engineering aspects. Various scenarios are analyzed to show the effectiveness of nonlinearity characteristic compensation mechanism to improve the performance of power conversion system and its applications as well. Last, but not least, the concept of analyzed power conversion system is applied to a typical fusion reactor and a marine propulsion system to explore other applications of the S-CO2 power conversion system. The DEMO model AB is selected as the reference fusion reactor. The computational analysis of this case gives a thermal efficiency of 42.44%. By adding a reheating layout, its efficiency can be enhanced to 43.1%. Engineering design of Naval Applied Vessel Island System (NAVIS) is briefly discussed as an example of the next generation concept of marine nuclear propulsion system. NAVIS is designed to suit the requirement of a compact, simple, safe and innovative integral fast reactor system. It is mainly powered by BORIS. To allow for significant size reduction and efficiency improvement, NAVIS adopted MOBIS and Nuclear Electric Propulsion Apparatus (NEPA) for its power conversion and propulsion system, respectively.