Progress in the reactor physics design of space reactors

The requirements for long life, high specific powers, and high working temperatures in the space environment have led to unique space nuclear reactor designs that are broadly based on liquid-metal reactor (LMR) technology. In particular, the liquid-metal-cooled nuclear power system for the SP-100 is being designed and developed as part of a ground engineering system (GES) program under the joint sponsorship of the US Department of Energy, the Department of Defense, and the National Aeronautics and Space Administration. The principal objective of the GES program is to demonstrate the technology for space power sources that can produce 10s to 100s of kilowatts of electric output under conditions of high operational reliability and rigorous safety requirements. The SP-100 reactor is a small, fast-spectrum, BeO-reflected configuration with enriched uranium nitride fuel pins, lithium coolant, and a niobium-based alloy for the cladding and structural materials. In addition, rhenium metal is utilized as a thermal neutron barrier outside of the core and as a fuel pin linear material in the core. The reactor for a 100-kW(electric) system provides a total of 2.4-MW(thermal) output, with a nominal inlet and outlet primary lithium coolant temperature of 1,290 and 1,350 K, respectively. The mission requirements for the SP-100 call for a 10-yr life with at least 7 yr of operation at full power