Rapporto di dettaglio sulla progettazione e realizzazione del sistema di purificazione dell'impianto LiFus6

This document deals with the solutions employed for the purification system of Lifus 6, a plant devoted to corrosion tests in flowing liquid Lithium, whose operations are going to start the next year. Reducing significantly the concentration of non metals (C, O, H and N) solved in Lithium, which highly enhance its corrosive behavior, is the purpose of the purification. The purification is performed through a Cold Trap, where the precipitation of the various binary non metals-Lithium compounds is promoted thanks to the reduction of the Temperature (200°C), and an Hot Trap, filled with a Titanium sponge getter, where Nitrogen concentration in Lithium is further reduced, thanks to the formation of a stable Titanium Nitride at 600°C. The residual concentration of Nitrogen in Lithium is online monitored by the Resistivity Meter, thanks to the existence of a linear relation linking it to Lithium resistivity, and by an offline Lithium analysis procedure, based on the transformation of small amounts of Lithium taken from the plant at defined time spans into Ammonia: this procedure, even if more time and work consuming, has the advantage of an higher sensitivity and may be useful also for the calibration of the Resistivity Meter. Both the Cold Trap and the Resistivity Meter are inserted into a secondary (purification) loop, which is characterized by a Lithium flow rate reduced to about 1% of Lifus 6 main loop, so to guarantee a sufficiently large residence time of Lithium through them and their best operative conditions. The purification system so defined will permit to reduce C, O and N content below 10 wppm, while H content will be reduced to about 60 wppm; on the other hand, no existing device could permit to precisely quantify a so small H concentration, so the efficiency of a more pronounced purification could in no case be verified.