Tritium loss in molten Flibe systems

An emerging issue relative to beryllium technology in fusion involves triti um interactions with molten beryllium-bearing salts. Innovative designs for fusion reactors, both magnetic and inertially confined, feature the molten salt mixture 2LiF . BeF2, commonly called Flibe, as a tritium breeder and coolant. Tritium is bred in the Flibe as neutrons from the plasma are absor bed by Li atoms, which then transmute to tritium and helium. Transmutation of tritium from Be also occurs. Among the issues to be resolved for such co olant systems is the potential loss of tritium from the Flibe coolant to th e walls of the system, particularly through heat exchanger tubes, and from there into secondary coolants or working fluids and the environment. Effect ively removing tritium from Flibe in clean-up units is also important. In quiescent or low Reynolds number flow, tritium movement through Flibe is governed by diffusion. For Flibe in turbulent flow, as in heat exchanger t ubes, transport is by turbulent mixing, and the same flow conditions and st ructural design features that maximize heat transfer to the heat exchanger walls will enhance the transport of tritium to those same surfaces. Analyse s have been performed to estimate the fractional loss of tritium through he at exchanger tubes and release rates from Flibe droplets in vacuum disengag ers in molten Flibe systems. The calculations suggest unacceptably large lo sses of tritium through heat exchanger tubes. The gravity of the implicatio ns of these estimates calls for experimental verification to determine if t ritium losses through molten Flibe heat exchangers or other Flibe systems c an really be so high and whether vacuum disengagers will really work. There is also a need for better information on evolution of tritium from Flibe d roplets in a vacuum. Several experiments are presently being planned to address these issues and are discussed. These include experiments to induce tritium in Flibe using spontaneous fission neutrons, experiments in flowing loops to evaluated tri tium losses through heat exchanger walls, and exploration of schemes for tr itium extraction from molten Flibe.