Design study of the emitter stem for the S-PRIME thermionic fuel element

The Thermionic Fuel Element (TFE) for the Space Power Reactor In-Core Moderated Evolutionary (S-PRIME) system requires the reduction or elimination of tantalum in the thermionic converter. In previous thermionic programs, the TFE emitter stem designs used tantalum as a transition joint between the emitter and the rest of the converter. This paper is a preliminary investigation of the effects of reducing or eliminating the tantalum in the emitter stem. A finite element program is used to compare the calculated stresses for different emitter stem designs. The results indicate that a reduced tantalum design has lower stresses, while a design with no tantalum has the lowest stresses. Further investigation is needed to verify these preliminary calculations and to asses the fabricability of an emitter stem without tantalum