Bimodal reactor for high and low space power

A bimodal space power system based on the gas-cooled particle bed reactor is described. The system is designed to continuously generate kilowatts of electricity during its lifetime, with the capability of switching to peak-load electrical generation on demand. The peak-load power can be a single long pulse or a series of shorter pulses. Total integrated operating time in the peak-load mode is on the order of one half-hour. In the continuous mode, the reactor uses inert gas (He or He-Xe) cooling in a direct, closed recuperated turbo-Brayton cycle. In the peak-load mode, the reactor switches to hydrogen-cooled open-cycle operation with turbo-expanders and exhaust of the waste coolant to space. The reactor is of the Fixed Bed Reactor (FBR) configuration, in which small diameter (∼1000 micron) particles are packed between outer (beryllium) and inner (zirconium-carbide) moderator reflectors. Fuel particles are held in place by a cool outer porous cylindrical frit (through which coolant enters), and a hot inner tungsten-rhenium frit. Fuel loading is ∼100 kg of 235U. Stored hydrogen coolant for open-cycle operation is the heaviest component of the total system weight