ANALYSIS OF YA-21U THERMIONIC FUEL-ELEMENTS

The Ya-21u unit of the Soviet-made TOPAZ-II power system has recently been tested at the Thermionic Evaluation Facility in Albuquerque, New Mexico. A change in the unit performance was measured during these res ts. In an attempt to identify the causes of this change performance, d ata were examined and used to estimate surface properties of electrode s of thermionic fuel elements (TFEs) of the power system. The effectiv e emissivity was estimated at similar to 0.03 to 0.035 higher than for as-fabricated TFE and cesiated work functions of the electrodes, whic h were higher than for as-fabricated TFEs. These changes in the effect ive emissivity and cesiated work functions, caused by gaseous impuriti es and air incursion in the TFEs interelectrode gap, lowered both the emitter temperature and the output load voltage thus contributing to t he measured decrease in output power.