The parameters of a thermoelectric reactor are determined by the radial dimensions of the EGC, in particular the external diameter d{sub EGC}, the diameter d{sub e} of the emitter, and the diameter d{sub c} of the channel fuel core. In this paper we consider a promising design, employing a five-layer collector package, including the collector proper, an insulation layer operating in cesium vapor, a guard electrode, and a dry insulation layer, all enclosed in a casing in contact with the EGC coolant. The total thickness of the collector package is 2.2-2.5 mm, for a range of d{sub EGC} of 18-50 mm. Given a reactor lifetime of 5-7 years, the emitter shell is made of hardened tungsten alloys, alloyed with niobium in thermal reactors and with tantalum in fast reactors, for an average specific energy conversion in the EGC of w{sub av} - 2-3 W/cm{sup 2}. For any diameter, the inner volume of the fuel core should have sufficient porosity to provide for redistribution of the fuel swelling toward the inside of the core. To ensure a lifetime of 7 years, the temperature of the EGC emitters fuel core should be limited to 1600{degrees}C, which limits the average specific conversion power.more » For a shorter lifetime the average specific conversion power and the emitter temperature may be higher. As the diameters of the fuel core and the emitter unit increase, the maximum permissible deformation of the emitter unit during the lifetime varies inversely with the emitter diameter. The thickness of the emitter shell must then increase with d{sub e} in order to keep the swelling within limits. For values of d{sub e} of practical interest, the dependence of the thickness of the emitter shell on the diameter for uranium oxide can be described as a linear function. The calculation procedure presented in this article can be used when {delta}{sub e} can be expressed by any given function of the fuel core diameter.« less