In the National Fusion Laboratory (LNF) in CIEMAT there is an extense background on the study of the tritium extraction system applied to a liquid metal-based breeding blanket.
CIEMAT has been the leading group for the engineering design of one of the four blankets considered in the preliminary phase of the DEMO design, the Dual Coolant Lithium Lead (DCLL). This breeding blanket is based on the use of a liquid metal alloy – the eutectic composition of lead-lithium (PbLi) – for tritium breeding. As mentioned, lithium is used to breed tritium; the lead (neutron multiplier) is used to achieve a TBR higher than 1. In particular, the eutectic composition of PbLi alloy (15.7% at. lithium) has been chosen because of its low melting temperature and its adequate stability not showing vigorous chemical reactions with air or water. Moreover, lithium determines the eutectic chemical activity and fine variation of Li title can significantly impact key properties as physical–chemical and solute transport properties.
The removal of tritium generated in the blanket is ensured by a closed PbLi loop which circulates the liquid metal to a dedicated Tritium Extraction System (TES). The aim of these system is to extract tritium at the highest possible rate to minimize the inventory in the liquid metal and, thus, to reduce possible leakages to other systems.
The background of the breeding blanket technologies group at the LNF has been reinforced through the HISMEFUS project (2014-2019), focused on the study of hydrogen isotopes in fusion. In addition, the set-up of the Liquid Metals Laboratory (LML) in CIEMAT has been an important step to expand CIEMAT capabilities in the liquid metals field. It includes the design and construction of two circuits for studying R&D technologies in flowing liquid metal: CLIPPER (CIEMAT LiPb loop for Permeation Experiments), and CiCLo (CIEMAT Corrosion Loop). CLIPPER and CiCLo have been already successfully designed, fabricated and commissioned.
One of the most promising technologies for tritium extraction from the liquid PbLi alloy is the Permeation Against Vacuum (PAV). This technique consists in the tritium diffusion from the PbLi, through a membrane in contact with the liquid metal, to a secondary chamber subjected to vacuum. The driving force is the pressure gradient generated by performing vacuum onto the external surface of the membrane. One of the key points to improve the process is the use of highly permeable materials for the membrane. Besides, there must be a chemical compatibility with the liquid PbLi alloy to avoid corrosion and malfunctioning of the component. For this purpose, the European research program has been focused on the PAV development using vanadium and niobium as membrane materials. Two main geometries are being developed: one based on rectangular flat channels for PbLi flows using vanadium plates and other based on a tubular arrangement of niobium pipes. At CIEMAT, efforts have been devoted to the experimental validation of a vanadium-based-PAV with a rectangular channel cross-section. Recently, the elimination of the membrane as extraction interface has been debated within the fusion field community and a new research line has been promoted by CIEMAT to compare both processes.
Fusion LUTHYER is a project dedicated to the testing and validation of non-commercial processes and prototypes that represent a critical point on the path to achieve nuclear fusion as an energy source.
Proyecto PID2022-140644OA-I00 financiado por MICIU/AEI /10.13039/501100011033 y por FEDER, UE
