Tritium Extraction from a DCLL Blanket Prepared by: Scott Willms (LANL) Collaborators: Brad Merrill (INL), Siegfried Malang (Consultant), Clement Wong (GA), Dai-Kai Sze (UCSD) Presented by: Jim Coons (LANL) Coordinating Meeting on R&D for Tritium and Safety Issues in Lead-Lithium Breeders 11 June 2007 Idaho Falls, ID LA-UR

Outline DCLL process overview Conventional separator T removal via vacuum permeator Model Mass transfer coefficient Parametric study DEMO design Issues Conclusions

DCLL process overview Use He to strip T from PbLi T permeation thru HX tubes Recover tritium from He He loop PbLi loop Avg. T2 breeding rate: sccm

Pressure in T2 separator tank if all tritium is contained (no permeation, no stripping, etc.)

Rough estimate for tritium removal pathways from PbLi with both tank pump off and HX permeation

Evaluating the possibility of using a vacuum permeator for tritium separation from Pb-Li Use Permeator to recover T from PbLi T permeation thru HX tubes Recover tritium from He He loop PbLi loop Avg. T2 breeding rate: sccm

Low Pressure Permeator Experimental Apparatus

Experimental Setup

Constant 25 sccm H 2 Increasing N C With 25 sccm H 2, the retentate and permeate are initially in agreement and ultimately breakthrough is observed at about 375 sccm.

Mathematical model for PbLi/T permeator A component balance describes the tritium mass fraction along the membrane length Tritium transport to the membrane surface is described by a mass transfer coefficient The effective tritium partial pressure at the membrane surface is given by the solubility Permeation depends on the permeability

Comparison of mass transfer coefficient results

The mass transfer coefficient for this system was estimated from general correlations 10 general correlations were considered The following correlation appeared to be the most appropriate: -- Harriott and Hamilton, Chem Engr Sci, 20, 1073, 1965 However, this correlation was developed with benzoic acid and glycerin-water mixtures at room temperature— considerably different from 700 C PbLi and tritium xixi x0x0 prpr p permeation through membrane liq bulk-to- surface mass xfer liq to solid xfer solid to gas xfer

Values used to solve the model

Using these base conditions the tritium concentration down the length of the permeator was determined

Performance depends strongly on the mass transfer coefficient

Wall thickness

Surface Concentration

Permeability

PbLi Flowrate

Feed concentration

Tube diameter does significantly affect performance Tube Diameter

Permeate pressure

Considerations for a practical PbLi permeator PbLi flowrate for Demo: kg/s With 1 cm dia. tubes and 5 m/s flow velocity: 7592 tubes Total Nb required for 5 m tubes: 2.6 tons Total cost for Nb: ~$0.5M (?) Diameter of vessel to contain tube cross sections + twice that area for space between tubes: 1.7 m This permeator is a substantial vessel, but one that can practically be constructed

While this initial analysis indicates that a PbLi permeator may be feasible, there are many issues that must be resolved Measured mass transfer coefficients for the PbLi-T system Compatibility of PbLi with Nb at 700 C Additional resistances to tritium permeation such as surface resistance? At the PbLi-membrane interface, is the effective partial pressure exerted by tritium indeed given by the solubility equation? (this may be a very different mechanism with a very different rate) What pressure can be practically maintained on the permeate side of the membranes? Will Nb tubes degrade due to reactions such as oxidation? Will a surface treatment be needed?

Conclusions Tritium permeation through the heat exchanger materials will be substantial and cannot be neglected Tritium can be recovered from helium streams with gas permeators and other technologies A reasonable plan for ITER TBM ancillary equipment is to include a helium bubbler on the PbLi loop and permeators on both He loops A potentially attractive option is a PbLi permeator to directly remove tritium from PbLi. Based on present information such a device might be practical. Whether or not it is actually practical would require considerable R&D