Simulation of tritium transport for the European Test Blanket System

Tritium and deuterium are two isotopes of hydrogen that will be used to fuel the fusion reactions in ITER. While deuterium can be extracted from seawater in virtually boundless quantities, the supply of tritium is very limited – only about thirty kilos of tritium are currently available in the world.

In DEMO, the tritium self-sufficiency is strictly requested which means that the amount of tritium consumed in a given period of time must be generated in the machine itself. In a tokamak fusion reactor this “in situ” tritium generation takes place thanks to the fusion neutrons leaving the plasma and interacting with a specific element – lithium – contained in the so called “breeding blanket”, a complex structure surrounding the plasma chamber. Because of its complexity and associated costs, the breeding blanket will not be present in ITER. However, ITER will provide a unique opportunity to test mock-ups of different possible breeding blankets concepts and connected circuits, called Test Blanket Systems (TBS), in a real fusion environment. Within these TBS, viable technologies for ensuring the expected tritium generation and recovery will be explored and validated, with the final aim to demonstrate the tritium self-sufficiency of the parent DEMO breeding blanket concept.

The tritium atoms are very small and then they may easily diffuse and permeate through all types of materials to which they are in contact. Tritium confinement is essential in order to recover the generated tritium and to strictly control the potential spreading of tritium within ITER.

In close collaboration with CIEMAT (Spain) and Empresarios Agrupados (Spain), F4E is developing a computer code based on the EcosimPro simulation platform which is able to predict the transport of tritium through the different components and materials of the two European Test Blanket Systems which will be installed inside the ITER machine. “With the help of a computer code based on advanced physics, we are able to predict over time the tritium transport along the different components and materials of the TBS and finally into the surrounding environment. The outcomes of the computer code are data of tritium concentration and flux in the form of tables and graphs which can be used not only to support the design of the two European TBS but also to comply with the nuclear safety requirements imposed by the Nuclear Operator (ITER Organization)”, says Italo Ricapito, F4E Group Leader working in the TBM Project Team. “The code implements complex mathematical models and, once completed and validated against the results coming from TBS experimental campaign in ITER, it could be used to support the design of a breeding blanket for DEMO. This is one of the most important objectives of the whole European TBM Project“.

The development of the code is currently at 70% completed – the basis and extra features are already in place. “We aim now to complete the work on the code and continue to implement more complex features mainly focusing on multi-physics issues and detailed operational conditions. However, the activities of code verification and validation will still require several years of work and a significant technical effort”, says Italo Ricapito.