Design study of molten-salt-type reactor for powering space probes and its automated start-up

Abstract

Space probes exploring the deep space need a noticeable amount of electricity for powering their instrumentation (5–8 kWe). The solar battery, however, is not able to afford this because of the extended distance between the probe and the sun. Furthermore, the radioisotope thermoelectric generator (RTG) may be extraordinarily sizable for this purpose. On the contrary, installation of nuclear reactor on the probes seems to be promising for the reasons such as its small mass, stability, and its high power density. Especially, the deep-space sample return mission has an essential demand for a nuclear reactor typically with the following specifications: 10-year reactor employment time, total system mass less than 500 kg, and electricity output more than 8 kWe. High power density is the key to realize these requirements. The thermal electricity conversion efficiency of a space reactor increases in accordance with the rise of the core temperature. Thus, in the present study, we propose a use of the molten-salt fuel considering that this type of fuel can achieve high core temperature over 1000 K. In addition to the space reactor for the space exploration, autonomic reactor control is extremely desirable because real-time control from the earth is difficult because of the long time lag of mutual communication. The molten-salt space reactor proposed in the present paper satisfies all the above essential demands primarily owing to the high-temperature operation availability. In addition, we concluded that the automatic reactor start-up in its orbit is feasible by virtue of introduction of novel reactivity-control devices proposed by Kambe (Kambe, Sato, Tsunoda. Space Nuclear Conference; 2007 June 24–28; Boston, MA. p. 36–45).