Detection of hydrogen as impurity in liquid lithium: An electrochemical hydrogen-sensor for IFMIF-DONES

• Published in: Fusion engineering and design 2022-05, Vol.178, p.113085, Article 113085
• Main Authors: Holstein, Nils, Krauss, Wolfgang, Nitti, Francesco Saverio
• Format: Article
• Language: English
• Subjects: Chemical sensors; Deuterons; Hydrogen; Hydrogen embrittlement; Impurities; Ion beams; Liquid lithium; Melting; Neutron irradiation; Niobium; Radiation hazards; Sensors; Tritium; Voltmeters
• ISSN: 0920-3796; 1873-7196
• DOI: 10.1016/j.fusengdes.2022.113085

IFMIF-DONES, the International Fusion Materials Irradiation Facility - DEMO Oriented NEutron Source, is the planned facility in Granada/Spain for fusion materials investigations using neutron irradiation in the scale of DEMO-oriented energies. This irradiation is generated by the interaction of deuteron beams with a liquid lithium flow-target system, containing huge amounts of this very reactive alkaline-metal. An important and critical issue during the operation of IFMIF-DONES is the enrichment of dissolved impurity components in the Li-melt and in the liquid melt concerning reactivity, corrosivity and radiation hazards. In the case of hydrogen, there is the danger of H-introduced embrittlement of the loop structure components as well as effects and hazards of the radioactive tritium. The application of liquid lithium in the scope IFMIF-DONES unconditionally hence requires a suitable impurity control. Regarding this subject, an electrochemical sensor for a continuous hydrogen monitoring is being developed in the frame of an international EUROFusion-WPENS task. This sensor was designed as single-rod-measuring-cell with niobium as the relevant membrane-material and a hydrogen conducting electrolyte. Potentials (Electro-Motive Force EMF) are being measured between the Li melt and a reference electrode by voltmeters with high impedances and can easily converted into H concentrations. Long-term tests (campaign-units of several hundred hours) in stagnant Li-melts with different sharply controlled hydrogen concentrations showed, that the sensor fulfills the requirements of chemical and mechanical stability and functionality also under harsher conditions (temperatures up to 500 °C). The obtained results and operational experiences will be discussed, e.g., concerning application windows, reproducibility and calibration needs. Additionally, recommendations will be outlined for upgraded systems and future qualification needs.