This work is aimed at improving the design and operation efficiency of thermosyphon evaporators in order to reduce the volume of aqueous radiochemical effluents. Operating experience and research in two-phase systems reveal that boiling accompanied by two-phase flow is highly affected by the flow dynamics and stability of the system. Therefore, a comprehensive experimental investigation is carried out. A well-instrumented experimental facility is designed and fabricated, in which six different thermosyphon reboiler designs are tested under a range of operating conditions. The experimental setup, the thermal hydraulics during boiling of aqueous solutions, and the results of the investigations are reported. The experiments reveal the effects of design parameters and operating process variables on the thermal-hydraulic performance. The primary process conditions, such as liquid submergence, temperature differential, and design parameters, influence the vapors produced, heat flux, recirculation flow rates, exit vapor quality, and resultant heat transfer coefficients.