Development of MCTFE - A computer modeling code for single and multicell cylindrical thermionic fuel elements

Abstract

This paper presents the modeling efforts undertaken to develop a computer code that is able to perform coupled thennal-hydraulic and thermionic analysis for both single and multicell Thermionic Fuel Elements (TFE). The code developed, given the name MCTFE (for multicell themionic fuel element), is a steady-state finite element code specifically designed to analyze cylindrical TFEs. It employs an iterative successive~ver-relaxation solution technique to solve for the temperatures throughout the TEE and a coupled themionic routine to determine the total TFE performance. The calculated results include: the temperature distributions in all regions of the TEE, the axial interelectrode voltages and current densities, and total TFE electrical output parameters including power, current and voltage. MCTFE generated results are presented that compare experimental data from the single cell Topaz-I1 type TFE and multicell data from the General Atomics 3H5 TEE in order to benchmark the accuracy of the code methods. TFEs of more than one cell utilize a different circuit arrangement. Figure 1 illustrates how single cell TFEs allow double ended current connections to each electrode. Multicell TFEs, however, require an endtoend series (flashlight) comection as shown in Figure 2.