UCLA

It is critical to be able to predict tritium transport in lead-lithium liquid metal (LM) blankets with great accuracy to provide information for fusion reactor safety and economy analyses. However, tritium transport processes are complex and affected by multiple physics such as magnetohydrodynamic (MHD) flow, yet there is no single computer code capable of simulating these phenomena inclusively. Thus the objectives of this research are: 1) to develop mathematical models and computational codes to quantify both tritium distributions throughout the blanket and the permeation loss rate from LM to helium coolant, and 2) to evaluate the key factors that govern tritium permeation and distribution.

To accomplish these objectives, a computational framework for analyzing tritium transport phenomena affected by multi-physics and geometric features has been developed. Models have been proposed to integrate multiple tritium transfer processes, including transport inside the LM MHD flow, transfer across the material interface, and permeation through the structural materials and into the helium coolant. Numerical schemes have been developed and implemented in the code to link the different transport mechanisms. The developed model and code have been validated against the data from the US-JA TITAN experiments on hydrogen transport through an α-Fe/PbLi system and in-reactor tritium release data from lead-lithium, and the modeling results agree well with the experimental data.

Parametric studies are performed to quantify the MHD effects, buoyancy effects, PES effects, and the uncertainties of transport properties. The MHD effects reduce the tritium permeation rate due to the higher velocity near the wall. However, the rate of decrease is reduced at higher Hartmann numbers. The buoyancy effect on tritium transport in the LM MHD flows is revealed. Its tritium inventory drops by 80%, and the permeation rate drops by 20% for an upward flow compared to a downward flow. If a PES is introduced on the wall parallel to the magnetic field, tritium loss rate increases by 15% because the velocity is reduced near the front wall. The range of permeation rate change on the basis of uncertainties of transport properties is also provided, and the effect of the uncertainty of tritium solubility is significant. Furthermore, as the FCI electric conductivity increases from 5 to 500 Ω-1m-1, the tritium permeation rate decreases by 46% due to the increasing velocity in the gap. Lastly, the difference in tritium permeation rates between dual coolant lead lithium (DCLL) and helium-cooled lead lithium (HCLL) blanket concepts is quantified. The tritium permeation loss percentage from the HCLL concept is about one order of magnitude higher than from the DCLL concept (~ 17%. vs. 1.2%). This is mainly due to a much lower velocity and thus a much higher tritium partial pressure for the HCLL concept.

The computational models and results stated in this work provide guidance on the lead-lithium liquid metal blanket designs to comply tritium control requirements with regard to the reduction in tritium permeation and inventory and on planning the experiments for database evaluation.