On the study of vapor condensation for the assessment of inertial fusion energy liquid chamber clearing

The work presented here investigates the condensation of excited vapors generated from a molten salt composed of lithium fluoride and beryllium di-fluoride. The material, denominated flibe, is used in the design of Inertial Fusion Energy Systems when the chamber protection scheme involves a liquid layer. The HYLIFE-II design is used as reference. The function of the liquid is to absorb the energy released by the fusion reaction. As a consequence, part of the liquid material vaporizes. Because of the high repetition rates necessary to keep the IFE power plant economically competitive, the issue of chamber clearing becomes a key feasibility factor. The motivation behind this work stems from the need of an experimental assessment of the achievable condensation rates of flibe vapors under IFE relevant conditions.; The experiments use a high-current electrical are to generate the excited vapors from a pool of molten salt. The vapor expands inside a scaled chamber and condenses in contact with the walls that are maintained at a controlled temperature. The experiments show that vapor clearing is characterized by an exponential decay with a time constant of 6.58 milliseconds in the density range between 5 x 1017 cm-3 and 2 x 1015 cm-3. The low limit of the range is determined by the impurities dissolved in the salt. Extending the result to the expected low limit of HYLIFE-11 (3 x 1013 cm-3), the period for vapor clearing is 68 milliseconds, which is compatible with the required 6 Hx repetition rate. SEM analyses of collecting plates revealed that condensation is inhibited on metal surfaces that lie in the direction perpendicular to the main component of the gas velocity. The phenomenon is analyzed and its implications discussed.; A numerical tool has been developed to evaluate condensation rates at the boundaries of a numerical domain in which the gas expansion is simulated with the Tsunami code, developed at UC Berkeley. The numerical results show that the experimental conditions can be partially simulated. The discrepancies with the experimental data are analyzed based on the code limitations and further development of the model suggested.