Development of an on-line sensor for hydrogen isotopes monitoring in flowing lithium at DONES

DONES (Demo Oriented Neutron Source) consists of an irradiation facility based in the nuclear stripping reactions that occur when one energetic deuteron beam impinges on a liquid lithium target flowing along an open channel. Since impurities enhance the erosion/corrosion effect, one of the challenging aspects on the development of the neutron source is the purity of the lithium. One group of impurities to be controlled are hydrogen isotopes in which the control of tritium as part of the produced impurities is mandatory due to its radiological risk. R&D activities are being performed for the development of different kinds of hydrogen sensors since there is no availability of commercial online monitors that could work under the lithium environment. As an extrapolation from other fusion applications, an online sensor based on the permeation against vacuum technique is proposed in this paper. The sensor design consists of a capillary tube made of a Pd/Ag membrane whose inner volume is subjected to vacuum promoting the H-isotopes permeation from the liquid. The vacuum line is connected to a mass spectrometer for the isotope detection. In addition, an experimental facility has been designed to experimentally demonstrate the feasibility of this monitor. It is made of a two-vessels system for lithium melting and H-isotopes detection. Furthermore, theoretical simulations have been carried out using the EcosimPro platform. Results show the expected behaviour of the sensor working under static conditions in the facility.