Low Power Thermal Reactor for Deep Space Probes.

Abstract

Deep space probes travel too far from the sun to use solar power and thus are dependent on Nuclear Power. Currently this is in the form of Radioisotope Thermoelectric Generators (RTG) which uses Pu-238. Pu-238 is not currently produced and may soon run out requiring production to be restarted; the only reasonable replacement radioisotope is Am-241. Both of these isotopes are highly toxic and the large masses needed for sufficient power pose nuclear proliferation concerns. The only alternative to radioisotopes is nuclear fission. Previous generations of space reactors have been designed for high power near Earth missions. As a result, previous reactor designs are ill-suited for the deep space missions. The feasibility of using small reactors of similar weight to current RTG’s is covered along with the design criteria for deep space probes. The reactor is designed with no moving parts, using burnable poisons for reactivity control throughout core life. Additionally, the core utilizes conduction for cooling, eliminating the need for pumps and coolant channels. The shielding requirements for the reactor are then calculated. Reactor safety concerns, effects of reactor transients and start-up are covered as well. The resulting reactor design has a core mass of 27.0 kg containing 8.68 kg of U-233. The use of U-233 reduces the proliferation risks relative to RTG’s and has 4 orders of magnitude lower radio-toxicity. The reactor will produce 2,112 WTH at a temperature of 640˚C for a lifetime of 200 years. The reactor will require a shielding mass of 43Kg. Using Stirling technology this should produce 500-800 WE with an engine/radiator mass of 50-80 kg. This produces a steady specific power of 4.1-5.3 WE/kg which is the equivalent to 6.0-7.7 WE/kg-RTG. The reactor design is well suited to the long duration deep space mission with a power supply lifetime significantly longer than any possible RTG. Due to the steady nature of the generated power and its long life, the specific power generation would exceed current RTG’s and match planned advances. In conclusion small low power fission reactors could be used to replace RTG’s for future deep space missions.