(Digital Presentation) Li Monitoring in Fusion Reactors: A Lithium Probe Based on Li6BaLa2Ta2O12 Solid-State Electrolyte for Molten Pb-Li
Authors: Hinojo Antonio , Nel-lo Marc , Pallarès Enric Lujan , Colominas Sergi , Abella Jordi 
Published: July 2022

Carbon-based energy sources stand for more than 85% of the total energy consumed. This energetic situation will no longer be sustainable in a near future. Fusion power can be a good option to face this energy challenge as they are expected to provide clean, safe, and low-cost effective energy. In future fusion reactors, deuterium and tritium are suggested to be used as fuel, releasing helium, neutrons, and large amounts of energy [1]. However, since there are no natural tritium sources, it must be in situ generated. Different concepts for tritium breeding modules (TBM) are considered to be constructed in nuclear fusion reactors [2]. One of the proposals is the so-called Helium-Cooled Lithium-Lead breeding blankets (HCLL). This TBM suggests the use of molten eutectic Pb-Li [3]. However, the transformation of lithium to tritium due to the breeding reaction will cause a decrease in the lithium concentration of the alloy [4].

6Li + 1n → 4He + 3H + 4.8MeV (1)

If the composition of the alloy changes, undesirable alterations in physical and chemical properties, such as the melting point or tritium diffusivity, will happen. For that reason, lithium concentration is a highly relevant parameter that must be controlled to ensure the correct operation of future fusion reactors. Therefore, new analytical tools for online Li monitoring in harsh chemical environments are required.

In this work, potentiometric sensors for lithium monitoring in molten Pb-Li alloys were constructed using Li6BaLa2Ta2O12 (LBLTO) Li-ion conducting solid-state electrolyte. Sensors were constructed by binding LBLTO sintered disks to alumina tubes using a glass binder. Pb-Li alloys used for the working (WE) and reference electrodes (RE) were prepared by mixing the required quantities of lithium and lead inside a glovebox with controlled oxygen and moisture concentrations (O2 and H2O < 0.1 ppm).

Experiments were performed inside a stainless-steel reactor placed inside a glovebox. In the RE, molten Pb-Li with 3 at% Li content was used. In contrast, Pb-Li alloys with concentrations close to the eutectic composition (between 13 at% Li and 19 %at Li) were used in the WE. Potentiometric measurements were performed at 500 ºC to simulate breeding blankets operation conditions. Experimental data was in good agreement with calculations using the Nernst equation.

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