The liquid lithium may be used in a magnetohydrodynamic generator to produce the electrical power. The lithium expansion in the generator is accomplished by a gas whose expansion process is kept nearly isothermal from the high rate of heat transfer from lithium to the gas. The near-constant temperature of lithium in the generator is produced by a chemical reaction with the oxidizer gas sulfur hexafluoride which is also used to expand lithium at a high velocity. Since the oxidizer gas is depleted as it reacts with the fuel lithium, another gas such as helium is introduced at the generator inlet to accelerate the liquid metal across the magnetic field which is applied perpendicularly to the main flow direction. The liquid metal lithium combustion with the sulfur hexafluoride yields a high rate of energy release and the products of combustion are liquids above 1065 degrees Kelvin. By operating the system below the consulate point temperature of 1638 degrees Kelvin, the combustion products can be easily separated and lithium recirculated by an electromagnetic pump or a nozzle-diffuser combination. The neutral gas helium can be also easily separated and may or may not be recirculated through the system. The proposed power system is estimated to yield a power density in excess of 30 MWe/m.sup.3 at an operating temperature of about 1200 degrees Kelvin and with an applied magnetic field strength of a few Tesla.