Studies on Low Specific Mass NFR/MHD Power Generation System for Space Applications

Abstract

The aim of this study is to examine a magnetohydrodynamic (MHD) power generation system for the space applications using a nuclear fission reactor as the heat source. This MHD system uses He/Xe mixed gas as coolant instead of alkali-metal-seeded inert gas. The interrelation between the specific heat of the coolant and the mass flow rate was examined. When the specific heat decreases due to increase of the Xe fraction, the mass flow rate must increase to keep the output power and plant efficiency constant. A regenerator efficiency of 100% and reactor output temperature of 1800 K or higher should be chosen for the highest plant efficiency of 56% and lowest specific mass of 1.4 kg/kW. This highest plant efficiency and lowest specific mass were also expected by optimizing parameters for enthalpy extraction and radiator temperature. This means achieving high plant efficiency or low specific mass gives different values for enthalpy extraction and radiator temperature. With a higher net electrical output power, lower specific mass is obtained. This explains why the present space MHD power generation system is better than other conventional space power generation systems for the high MW-range output power.