Over the last two decades the idea of using liquid wall protection has been employed in a number of the inertial fusion energy (IFE) power plant design studies. The renewable liquid not only protects the first wall from the x-ray and debris damage but can simultaneously be used as the primary tritium breeding and energy carrying medium in due course a simplified design. In addition, advantages including plant life time structures and a lower cost of electricity were realized in the thick-liquid wall protection scheme. Among the possible choices of liquids for the liquid wall protection, Flibe seems to be the preferred choice based on the vapor pressure consideration and neutronic performance. For example, the thickness of liquid needed to satisfy the damage criteria by Flibe is about 56 cm, whereas much thicker liquid lithium and Li17Pb83 of > 160 and 152 cm, respectively, would be required for a dpa of <100. However, the formation of TF from the tritium produced in the Flibe can be very corrosive to steel based alloy. Even if the bred tritium can be converted into T2 form by appropriate control of the Flibe chemistry, the tritium confinement becomes an issue. Furthermore, the incoming liquid velocity required to clear droplets for achieving a high repetition rate involves a turbulent jet to be formed inside the chamber. Past experimental studies of turbulent breakup have shown that the location of the onset of the breakup caused by the internal turbulent eddy is inversely proportional to the jet fluid Weber number. The basic properties of liquids indicate that this would occur at 12 cm away from the jet exit for the Flibe jet and about 46 cm for the lithium jet. Consequently, Flibe has a higher uncertainty associated with jet stability. The evolution of drop size as jet proceeds downstream is analyzed to examine whether further breakup would interfere with passage of the target or beams.

The question of whether a thick or a thin layer liquid IFE chamber wall protection scheme currently envisioned will work in practice awaits experimental resolution. Nevertheless a comprehensive assessment of the optimum liquid option for an IFE chamber wall is essential considering that the choice of the liquid will impact R&D and the industrial investment. The present assessment focuses on performance feasibility issues concerning hydrodynamics, compatibility, wettability and chemical stability, while small-scale experimental programs are under development to facilitate this assessment.