Development of reactors with thermionic converters for cosmic power plants in the USA

The status of nuclear reactors with thermionic converters in active cores for space power plants is considered. Problems of development of high-temperature fuel for such reactors as well as those of selection of materials for fuel cans, being at the same time emitters of the thermionic converters, are discussed. According to the SP-100 research program developed in the USA the plant with capacity of 1 MW is to be placed into orbit in the first half of 90-th. Irradiation tests of fuel elements with different combinations of fuel and can materials carried out at the temperature of 1100-2200 K and burnup of 0-5 % have shown that most resistant are cans on the base of Ta and Nb alloys with W diffusion barrier layer between the fuel and can. It is concluded that most of the fuel element failures correlate with excessive fuel density (more than 90% of theoretical one), excessive oxygen content in the fuel (more than 1000 mln-1) and anomalous hydrogen brittleness of Ta base alloy cans. UO2 with stoichiometric content possessing good compatibility with can is the most acceptable as a fuel