Membrane gas-liquid contactor for tritium extraction from Pb-Li alloys

Abstract

Abstract Gas-Liquid Contactors (GLC) have been studied for the extraction of tritium from Pb-Li blankets, typically consisting on bubble, packed or spray columns. Recent researches propose the use of Permeators-Against-Vacuum (PAV) in which dense metal membranes (V, Nb, Ta) are immersed into flowing Pb-Li: here the hydrogen isotopes pass through the membrane wall and are collected in the permeate side with help of vacuum. In this work, permeation behavior of a Membrane Gas-Liquid Contactor (MGLC) that combines both GLC and PAV concepts is presented. This device includes a porous ANSI 316 L stainless-steel membrane which is immersed into a Pb-Li alloy. Hydrogen isotopes are first absorbed into the liquid metal and then extracted through the membrane by vacuum pumping or purging with inert gas. In fact, the liquid metal penetrates the pores of the porous membrane then realizing a gas-liquid interface through which the hydrogen isotopes mass transfer takes place. The pore size of this membrane has been selected according to the Washburn equation so that the Pb-Li behaves as a “non-wetting liquid” and does not enter the vacuum/inert gas phase where leaks of liquid metal are not allowed. The study describes the preliminary design for the MGLC device working with a porous metal membrane and its experimental characterization at 340–370 °C and 270 kPa. A mass transfer model for the tritium extraction from Pb-Li is also presented, comparing both PAV and MGLC alternatives.