TRITIUM - Tritium Transport and Process

Fusion power is based on the fusion of deuterium with tritium creating He-4 and releasing a significant amount of energy. Special attention must be paid to the production systems, the test blanket modules (TBM) and the auxiliary recovery systems.

EAI, in collaboration with Fusion Spanish Lab (CIEMAT), has developed a set of libraries for the simulation of systems and processes involving hydrogen isotopes for the study of transport phenomena and of physico-chemical processes related to the extraction and purification of tritium, that have been used for the toolkits described herebelow:

Models for different situations have been developed:

• Test Blanket Systems (TBS)
• Tritium Plant

Test Blanket Systems (TBS)
TBMs are the units used for tritium generation and they are accompanied by ancillary systems that recover the generated tritium. The global system is the TBS, and can be simulated using TRITIUM_TBM toolkit. This toolkit includes the main elements needed for modeling TBS, which are continuously reviewed and enhanced in order to include additional effects or add more detail to the existing components, as well as to adjust the model to the increasing level of definition of these systems.

Key features:

• Different combinations of species can be selected by the user to be considered in the model simulation (H, D, T, T2, HT, H2O, etc.)
• 1D diffusion model in materials (LiPb, Eurofer, AISI 316L, etc)
• Properties are dynamically calculated as a function of temperature for each species in each material
• Interface between materials, or between materials and gas enclosures, controlled by surface phenomena (disassociation and recombination) or by diffusion
• 1D piping for the circulation of liquid metal (LiPb) and for gases
• Components for HCLL (Helium Cooled Lead Lithium) and HCPB (Helium Cooled Pebble Bed) TBM configurations are included
• Ancillary systems for HCLL TBS included as components in TRITIUM_TBM library: PbLi_Loop, TRS (Tritium Recovery System), HCS (Helium Cooling System) and CPS (Coolant Purification System)
• Ancillary systems for HCPB TBS included as components in TRITIUM_TBM library: TES (Tritium Extraction System), HCS and CPS
• Additional components used in ancillary systems for special equipment: TEU (tritium Extraction Unit), Pebble, etc.
• Generation rate and profile can be easily modified.

Tritium Processing Plant
Due to the small amount of tritium available, it is very important in fusion reactors to recover the unburned tritium present in the exhaust gases of the reactor. With this aim, a combination of different processes (permeation, distillation, etc. ) recovers as much tritium as possible from the gas stream leaving the reaction chamber. The processes are modeled in the TRITIUM_PLANT library

Key features:

• Different combinations of species can be selected by the user to be considered in the model simulation (H, D, T, T2, HT, H2O, etc.)
• 1D diffusion model in materials (LiPb, Eurofer, AISI 316L, etc)
• Properties are dynamically calculated as a function of temperature for each species in each material
• Interface between materials, or between materials and gas enclosures, controlled by surface phenomena (disassociation and recombination) or by diffusion
• 1D piping for the circulation of liquid metal (LiPb) and for gases
• The main units for tritium processing are included:
  • Vacuum Vessel where tritium is consumed
  • TEP (Torus Exhaust Purification): using a combination of permeators and reactors
  • ISS (Isotopic Separation System): cryogenic distillation columns
  • SDS (Storage and Delivery System)
• Auxiliary systems: equilibrators, heat exchangers, etc.

These elements are currently undergoing improvement, mainly with the following aims:

• to increase the level of detail included in their formulation (e.g. energy balances in the packed columns used for ISS)
• to provide the library with components representing additional units, such as WDS, currently under development.
• to correct minor errors found after the version was delivered and to enhance the usability of the toolkit according to the users’ requirements.

The following user case shows the model of the HCPB TBM and its ancillary systems:

Tritium is generated (in back to back pulses) inside the HCPB, in the Pebbles encapsulated inside the TBM-HCPB component. The purge gas drives tritium to the TES where it is adsorbed in getter beds. Additionally, the TBM is cooled by Helium that needs to be purified in the HCS and CPS for extracting the tritium that has permeated through the TBM walls.

The following plots show the tritium inventory evolution in some elements of this TBS.

Together with the total amount of tritium generated, the milligrams of tritium cumulated in the TBM (e.g. solubilised in the gas or materials):

The aim of the TES is to recover as much tritium as possible and store it in getter beds. The amount of tritium in the TES getter beds follows this evolution over time:

As shown in this plot, tritium is properly recovered in the TES because the high speed of He taking tritium to the getter beds reduces its permeation through the walls. However, these variables (permeation to the environment, tritium solubilised in the equipment walls, etc) are calculated during the whole simulation and can be plotted as well. As an example, the cumulative amount of tritium permeating from TES to the environment follows: