Electrical characteristics and thermal analysis of a TOPAZ-II single-cell thermionic fuel element test stand

Abstract

The general objectives of this research are to investigate the electrical and thermal characteristics of the TOPAZ-ll thermionic fuel element (TFE) test stand which allows testing of a single TFE. Detailed cross sectional drawings have been developed and a one dimensional network has been created for use in a thermal model of the FTE test stand. Critical resistances in the network are identified as the regulated helium gap, the cesium filled interelectrode gap and the cooling water channel. Experimental data show the FTE operational dependence upon cesium pressure in the interelectrode gap. Thermionic performance at varying thermal input power levels has been analyzed based on the determined optimal cesium pressures which range from 0.4 torr at about 1000 Watts to 1 torr at about 3000 Watts input. Thermionic efficiencies can be as high as 7 %, but the low thermal inputs have efficiencies of about 1.5 %. Results provided by the FTE test stand are compared to the TOPAZ-II reactor system performance. Operation of the reactor at much lower thermal power (not previously analyzed) may produce useful electrical output (1 kilowatt-electric) for "housekeeping" purposes.