[en] A thermionic converter unit for use in a nuclear reactor to generate current, which can be constructed at low cost and which efficiently utilizes the nuclear fuel, is described. The reactor utilizes an array of thermionic emitters whose peripheries are fluted so that a bulge of one emitter interfits the depression of another to permit compact mounting, each emitter having several fuel passages located in the bulged portions for holding nuclear fuel and having a central collector passage for holding a thermionic collector. The emitters are constructed of rods of tungsten containing a small amount of thorium oxide, the thorium oxide not only improving the machinability of the tungsten but making it an efficient emitter. 5 claims, 3 figures