TITAN/IEA Liquid Breeder collaboration topics and technical issues

1. TITAN/IEA Liquid Breeder collaboration topics and technical issues Dai-Kai Sze, UCSD Presented at the FNS/TBM meeting UCLA, September 19-20, UCLA

2. TITAN Progress • The ORNL/NIFS agreement on the TITAN collaboration has not been formally signed. • Recent discussion between ORNL/NIFS has been encouraging. • It is expected that we can reach an agreement which is acceptable to both sides. • Japanese funding, and technical progress will move ahead after we reach the agreement.

3. TITAN Tasks • Task 1-1 PMT activities based on PISCES and TPE. • Task 1-2 Tritium/LiPb interactions based on STAR • Task 1-3 MHD activities • Task 2 will be discussed at the ORNL workshop

4. IEA collaboration • Tritium/LiPb interactions • LiPb/water reactivities • Liquid breeder data base and web site development • Be/FS coating fabrication and irradiation* • MHD activities * *to be further discussed

5. Tritium/LiPb interaction • The data base for tritium solubility in LiPb has large uncertainties (by about a factor of 100). • The relationship between partial pressure/tritium concentration relationship is uncertain. • Efficient tritium recovery process has not been developed. • Tritium permeation barrier development has not reach the target. • Irradiation will reduce (eliminate?) the barrier effect.

6. Tritium solubility • The relationship between the tritium partial pressure and the tritium concentration in the LiPb is the most important information for the tritium system. • The reported tritium solubility has an uncertainty of ~100. • The most recent reported solubility is about a factor of ~20 differ from the reference number. • Various reasons contributes to this uncertainty.

7. Methods of measurements • The solubility can be measured by either absorption or desorption methods. • The resulted tritium solubility's are very different. • This means that the equilibrium situations were not met.

8. Partial pressure/concentration relationship • It has been assumed that the tritium solubility in LiPb obeys Sievert’s law. • There are different reasons that it does not obey Sieverts’ law. • If it does not obey Sievert’s law, force the results to obey Sievert’s law will produce large errors. • This maybe the key problem on the accuracy of the solubility. • The next few VG’s will summarize why the solubility may not obey Sievert’s law.

9. Effect of concentration • It is well know that tritium solubility in metals, such as Li, obey Sievert’s law at low concentration of T, due to the existing of the LiT from dissolved in Li. • As the tritium concentration in Li increase, LiT becomes supersaturated, and precipitate out. • The effective concentration of LiT dissolved in Li remains to be consistent. • The tritium partial pressure over Li becomes constant, independent of real T concentration inside the Li.

10. Effect of chemical form • Tritium solubility in the Li obeys Sievert’s law because of the formation of LiT. • In LiPb, the chemical activity of Li is very low. • Tritium may not exist in the LiT form/ • If tritium is chemically bounded with Pb, the chemical form will be PbT4. • The tritium partial pressure will depends on the concentration to the fourth power. • If tritium dissolve in the LiPb in the T2 form, and tritium partial pressure will be proportional to the concentration (Henry’s law)

11. Effect of hydrogen • Due to the expected low tritium solubility in the LiPb, the tritium concentration in the LiPb will be very low. • It is very possible that the background hydrogen will be much larger than the tritium. • If this is the case, the tritium partial pressure over the LiPb (in the HT form) will be proportional to the tritium concentration.

12. Effect of Oxygen • Based on the chemical analysis of LiPb, there is a very large O concentration existing in the LiPb. • The O may react with tritium to form Q2O. • If this is the case, the tritium will not exist in the elementary form, but in the oxide form. • The tritium solubility is no longer an issue. • The Q2O solubility becomes an issue.

13. Other problem • If we want to measure the partial pressure/concentration relationship, we need to measure both the tritium partial pressure over LiPb, and the tritium concentration in the LiPb. • It is easy to measure tritium partial pressure over the LiPb. • However, no direct method has been developed to measure tritium concentration in the LiPb. • Indirect measurement, such as by mass balance, will cause large error.

14. Other ProblemsTritium recovery • Tritium recovery process did not obtain the required efficiency (~>80%). • The best efficiency demonstrated was ~30%. • To improve the process, or develop another process, rate limiting steps must be identified. • Knowing rate limiting step, the process can be optimized toward that step to improve the recovery efficiency.

15. Permeation barrier • The development of tritium permeation barrier has not been successful. • Irradiation has show to reduce or eliminate barrier effect. • If He is used as coolant, large amount of tritium will permeate into the coolant. • Efficient tritium recovery from the high mass flow rate of He, to a partial pressure ~ 10(-7) Pa has not been demonstrated.

16. Conclusion • Tritium recovery and control for a LiPb based blanket (and TBM) required much more work. • The interaction between tritium and LiPb is not clear at this time. • Therefore, the functional relationship (Sievert’s law) between the tritium partial pressure and tritium concentration is unknown. • An efficient tritium recovery process has not be demonstrated. • The development a reliable tritium permeation barrier within the radiation environment will be needed. • If tritium permeation barrier can not be developed, an efficient tritium recovery process from the high mass flow of He (and water) will be required.

17. Other possible IEA collaboration topics • Development of a Be coating on FS, and testing under irradiation. • Liquid breeder data and web site development. • MHD experiments and code development. • LiPb/water chemical reaction. • Other possible topics for Li based blanket.