Hydrogen Transport Membranes in Nuclear Reactor Cooling Systems

Hydrogen Transport Membranes in Nuclear Reactor Cooling Systems 

In the patent by Hill, an aUoy of titanium containing 13 wt%vanadium, 11 wt% chromium and 3 wt% aluminum was developed as a hydrogen transport membrane material [12]. In this alloy, the crystal structure of titanium, which is normally hexagonal below 1153 K (880 °C), is stabilized in its high-temperature body centered cubic allotropic form. The body centered cubic crystal lattice is preferred for hydrogen transport. This titanium alloy was found to have hydrogen permeability superior to that of pure palladium in the range 300-450 °C (573-723 K) 

For all hydrogen transport membranes, the partial pressure of hydrogen in the permeate must always be maintained at a partial pressure lower than that of the hydrogen in the source in order to maintain a net hydrogen flux from the source to the permeate [14]. For membrane applications with molten metal cooling fluids, in which upstream partial pressures in the retentate can be equivalent to only 2.7 x 10 Pa to 6.7 x lO Pa (2.0 x lO torr to 5.0 x 10 torr) [15], the partial pressure of hydrogen in the permeate must be kept exceptionally low. 

Because diffusion is simply rapid, random, translational motion of atoms and molecules, hydrogen in superpermeable membranes will travel just as quickly from the permeate side of the membranes to the retentate side, as it does in diffusing from the retentate to the permeate side. From the fundamental laws of diffusion, diffusion will tend to eliminate concentration gradients across a membrane, and at equiUbrium the net flux across a membrane will be zero [14]. For superpermeable membranes, equilibrium will be very quickly approached, unless hydrogen is removed extremely rapidly from the permeate side of the membrane. 

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