New developments of hydrogen impurity online-monitoring in liquid lithium of IFMIF-DONES

Abstract

On the way to future nuclear fusion power plants, the International Fusion Materials Irradiation Facility (IFMIF) – DEMO Oriented Neutron Source (DONES), is an important key element between ITER and DEMO to study before the influence of DEMO-neutron irradiation on foreseen fusion materials. The core of DONES, currently under construction near Granada, Spain, is based on a circuit containing liquid lithium at elevated temperatures acting as a functional material for the (d,n)-Li reaction in a materials test cell. In addition to this actual function of DONES, there are important aspects of maintenance in which hydrogen isotopes are generated under operating conditions and dissolved in this aggressive and very reactive alkali metal. This implies strong unfavourable effects on the applied structural materials, e.g. hydrogen embrittlement and others.To counteract these unfavourable effects, endangering the safe operation, an Impurity Control System (ICS) is an integral part of the DONES instrumentation. As part of the tasks of the European Neutron Source (ENS) to develop redundant systems for monitoring impurities, a special sub-task was defined for the development of an electrochemical H-sensor for concentrations in liquid lithium, ECHSLL. It is determined by detecting the electrical potentials of the lithium melts compared to a standard Li-based chemical reference system. This allows an inherent material property to be directly correlated (i.e. through appropriate electrochemical instrumentation) with chemical concentration values. This article presents important advancements in the applied ECHSLL technique, such as improving laboratory measurements from stagnant conditions to dynamic and realistic flow conditions of the liquid lithium material, as well as appropriate approaches to overcome the challenges in distinguishing the hydrogen isotopes by ECHSLL system (protium and deuterium among given laboratory conditions).