1. Review of Tritium Permeation Barriers Rion Causey Sandia National Laboratories Livermore, CA 94550 Presented at: ITER TBM Project Meeting, UCLA February 23-25, 204 Materials & Engineering Sciences Center Atoms to Continuum

2. Non-Replenishing Tritium Permeation Barriers Do Not Work Well!! Materials & Engineering Sciences Center Atoms to Continuum For various reasons, permeation barriers have not provided the reduction in permeation that has been desired. Barriers that have provided Permeation Reduction Factors (PRF’s) of 1000 or greater in the laboratory, have later provided PRF’s of 10 or less in the real application. Most of the permeation barriers that have provided PRF’s of 1000 or greater consist of oxide layers. The primary reasons for the reduction in PRF’s during the application include chemical erosion or cracking of the barrier.

3. Some materials naturally have lower permeabilities for hydrogen isotopes Materials & Engineering Sciences Center Atoms to Continuum Tungsten has a very low permeability, but is too heavy. Aluminum also has a low permeability, but it has no strength at 500 o C. At 500 o C, copper is about 30 times lower than Manet

4. What amounts of tritium would be released based on these permeation coefficient?? Materials & Engineering Sciences Center Atoms to Continuum Consider the following hypothetical situation (provided to me by Dai Kai) The heat exchanger will operate at a temperature of 500 o C. The surface area of the heat exchanger will be 10,000 m 2. The pressure of tritium in the heat exchanger will be 1 Pa. Assume a wall thickness of 2 mm.

5. The release rates are HIGH!! Materials & Engineering Sciences Center Atoms to Continuum Permeation coefficient for Manet is about 3x10 -6 cc(stp)/(s-cm-atom 1/2 ) The permeation rate is approximately 100 grams/day Using a duplex coextruded steel/copper tube reduces the effective permeation coefficient by about 30, yielding about 3 grams/day (30,000 Ci/day) Even with a permeation barrier on the Manet tubes (and the achievement of a PRF of 1000) still yields a permeation rate of 0.1 grams/day (1000 Ci/day)

6. As recommend by Dai Kai, I have looked into a product by Alon Processing Inc. Materials & Engineering Sciences Center Atoms to Continuum Alon Processing Inc. produces heat exchanger tubes that have aluminum diffused into the base steel. Aluminum at concentrations of approximately 20at% exist for the first 0.5 to 1.0 mm. They claim this is not a coating, but a material that has an alloyed region quite deep into the steel.

7. Hydrogen permeation has been measured for these alonized tubes Materials & Engineering Sciences Center Atoms to Continuum In the permeation experiments, a mixture of water, acetic acid, sodium chloride with hydrogen sulfide added was used at the hydrogen source. For the alonized layer on the inside only, a PRF of 100 was achieved. When the alonized layer was placed on both inside and outside, a PRF of 500 was achieved.

8. Conclusions Materials & Engineering Sciences Center Atoms to Continuum In future tritium burning fusion devices, holding the tritium permeation rates to reasonable values is going to be very difficult. It is likely that a double tube design or an intermediate heat exchanger will be required. The material produced by Alon Processing Inc. appears very interesting and should be tested again for hydrogen permeation with appropriate gas pressures.