Substantial thermionic space reactor development programs were conducted in the U.S., France and Germany in the period 1963–1973, and the US resumed a significant thermionic nuclear fuel element development program in the period 1983–1993.
Znatan program razvoja termioničkog svemirskog reaktora bio je proveden u SAD-u, Francuskoj i Njemačkoj u razdoblju 1963-1973, i SAD nastavlja značajan program razvoja termioničkih elemenata nuklearnog goriva u razdoblju 1983-1993.