Tritium Research in TITA Information Required

1. Tritium Research in TITA Information Required Dai-Kai Sze, UCSD Phil Sharpe, INL Presented at the US-ITER TBM Meeting UCLA, LA, CA Feb. 14-15, 2007

2. Proposed Tritium Research Activities in TITAN Collaboration(formerly known as JUPITER-III) Involved Parties considered several issues that require attention for progress in developing successful and Plasma-facing Components and PbLi Blankets : 1. Key technical items for tritium behavior in PFCs: • Plasma-driven permeation behavior and effect of surface conditions • Irradiation and implanted He effects on retention and permeation • Mixed materials retention behavior 2. Key technical items for tritium in blanket systems: • Solubility in PbLi • Recovery methods from PbLi and He flows • Transport barriers resistant to thermal cycling and irradiation • Permeation behavior at very low partial pressures over metals

3. TITAN Task 1-1: Fuel behavior in Plasma-facing Components • Plasma driven permeation/Tritium retention (TPE) • - Mono-materials (W, RAF) non-irradiated & irradiated • - Mixed-materials, Duplex materials (Be on W, W on RAF) • Mixed-material PSI W/Be systems (PISCES) • - Formation conditions • - PMI behavior using D & He plasma • - W sputtering & evaporation, hot spot formation, etc. • - Surface modification • Effects of Helium on Tritium retention/permeation and mixed material formation (PISCES and TPE) TITAN Task 2-1: Tritium Behavior in Irradiated PFC Materials • Plasma- and gas-driven permeation in irradiated W • Transport properties of irradiated Be/RAFS bonds • - Influence of He and bubble formation • - Intermetallic formation and dynamics of bond characteristics

4. TITAN Task 1-2: Tritium Behavior in Liquid Breeder Blankets • Solubility of T in PbLi at Blanket Conditions • - Measurement of tritium solubility at low partial pressures (required for tritium inventory control) • - Explore possible deviance from Sievert’s Law (indicative from other LM results, e.g. Li) • Concentration Effects of T Permeation in Structural Materials • - Linear vs. Sievert’s behavior? Devise measurement for dissociation/ recombination rates • - Explore influence of surface characteristics and treatment • Tritium Extraction from PbLi at Blanket Conditions • - Measure mass transport across liquid-vapor interface for vacuum disengagement or window permeator designs

5. What information do we need? • Solubility of tritium in LiPb • Efficient tritium recovery method • Development of reliable tritium diffusion barrier • Establish the pressure dependency of tritium permeation.

6. Tritium solubility • Most tritium solubility measurements were done by using hydrogen at high H2 partial pressure. • It was assumed that the Sievert’s law applies and extrapolated to much lower tritium partial pressure (< 1 Pa). • For most liquid metals, the hydrogen obeys Sievert’s law only at rather low tritium partial pressure. • Force fitting the Sievert’s law may result large error if extrapolated to very low partial pressure.

7. Tritium solubility uncertainty • Early comparison observed a two order of magnitude difference in Sievert’s constant from different measurements. • Recent report at the St. Petersburg workshop suggested a factor of 18 difference between the new results and the reference solubility.

10. Work Required • It is important to establish the complete phase diagram between T and LiPb. • Depends on the tritium concentration, the partial pressure /concentration can either obey, or not obey, the Sievert’s law. • We need to measure the tritium solubility down to a partial pressure << 1 Pa. • For such a low partial pressure and low concentration, it is necessary to use tritium for measurement and control purpose. • STAR is set up to do this.

11. Tritium recovery • Much work has been done, mainly in EC, to develop an efficient tritium recovery process. • However, the efficiency of the recovery process is only about 20%. • The target recovery efficiency is about 75%. • Improvement of the EC process, or the development of a new process, will be necessary.

12. What can we do? • Permeation window is a possible process to recover tritium from LiPb. • Permeation depends on the square root of tritium partial pressure. Therefore, tritium solubility information will be necessary to the permeation method. • Surface contamination is a key concern for tritium permeation. • Are there other methods?

13. Permeation coating • There have been much efforts on development of tritium permeation coating to reduce tritium permeation by about a factor of 100. • This goal has not been reached for a large surface area. • Some reported that permeation reduction factor can be much reduced under irradiation. • Under TITAN program, Japan side will develop coating, and US side will test the effectiveness of the coating.

15. Tritium permeation • The usual assumption is that tritium permeation is proportional to the square root of tritium partial pressure. • Theoretical prediction is that, at low pressure, tritium permeation will be proportional to the tritium partial pressure. • This pressure dependence of tritium permeation is important for tritium control, and the tritium recovery method based on permeation window. • TITAN will investigate the pressure dependence on permeation at low tritium partial pressure.

16. Conclusion • There is not sufficient information on many tritium related issues for the LiPb system. • One of the key problems is that we do not have the complete T/LiPb phase diagram. • To do experiments at a hydrogen partial pressure relevant to the blanket condition, tritium has to be used. • STAR will be a key facility to do this work. • The results from this work will be useful for all the LiPb based blankets. • The permeation barrier development will be useful of other type of blankets, such as He-cooled and water-cooled solid breeder blankets.