| A transient code (TFETC) for calculating the temperature distribution throughout the radial and axial positions of a thermionic fuel element (TFE) has been successfully developed. It accommodates the variations of temperatures, thermal power, electrical power, voltage, and current density throughout the TFE as a function of time as well as the variations of heat fluxes arising from radiation, conduction, electron cooling, and collector heating. The thermionic fuel element transient code (TFETC) is designed to calculate all the above variables for three different cases namely: (1) Start-up; (2) Loss of flow accident; and (3) Shut down.; The results show that this design is suitable for space applications and does not show any deficiency in the performance. It enhances the safety factor in the case of a loss of flow accident (LOFA). In LOFA, it has been found that if the mass flow rate decreases exponentially by a {dollar}-{dollar}0.033t, where t is a reactor transient time in seconds, the fuel temperature does not exceed the melting point right after the complete pump failures but rather allows some time, about 34 seconds, before taking an action. If the reactor is not shut down within 34 seconds, the fuel temperature may keep increasing until the melting point of the fuel is attained. On the other hand, the coolant temperature attains its boiling point, 1057{dollar}spcirc{dollar}K in the case of a complete pump failure and may exceed it unless a proper action to trip the reactor is taken. For 1/2, 1/3, and 1/4 pump failures, the coolant temperatures are below the boiling point of the coolant. |
