Thermionic fuel element with a gas removal system in the form of end porous pellets within uranium dioxide core

The thermionic fuel element (TFE) design is described in which the end pellets of UO₂ with open porosity stabilized to thermal and irradiation sintering are used to provide the removal of fission gas from a fuel core inner cavity. It is shown that the total height of solid end porous pellets must be no less than the thickness of the annular pellets placed on the core rest part to prevent blocking of the open porosity by UO₂ condensate under conditions of an axial mass transfer within the core. A two-dimensional mathematical model is stated and computer code is described for porosity behaviour calculation at TFE operating parameters. The results of the calculated investigations into kinetics of porosity changes are given and compared with the experimental data. It is also shown that emitter deformation in places of the solid porous pellets does not limit TFE normal operation during a lifetime of 7-10 years