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

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.

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

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

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.

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.

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.

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.

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.

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)

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.

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.

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.

Other Problems Tritium 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.

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.

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.

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.