Hydrogen Transport Model in Eutectic PbLi for Data Evaluation in an Absorption-Desorption Experimental Facility

The determination of the transport parameters of the hydrogen isotopes in the eutectic lead-lithium (PbLi) alloy represents a key issue for the design of the different breeding blanket systems that are being developed based on this liquid metal. This is the case for the dual-coolant lithium-lead blanket where the values of the Sieverts’ constant and diffusivity will delimit the magnitude and the kinetics of the induced tritium flux produced by the breeding blanket toward the circuit of He for the refrigeration of the structures. In addition, the design (sizing and efficiency) of future tritium extraction systems of the breeding alloy or the He coolant purification system will be defined on the basis of these transport parameters.

Taking into account the current literature, there exists a very wide band (even more than three orders of magnitude) in the experimental results for the Sieverts’ constant obtained by different research groups using different experimental techniques. This dispersion band in terms of solubility is not acceptable from the point of view of the design of a breeding blanket for a fusion reactor. With the aim of reducing this dispersion of results, the Absorption-Desorption facility available at the University of the Basque Country (UPV/EHU) has been upgraded and new samples of high quality PbLi will be measured in the near future in collaboration with CIEMAT.

In this work, a complete theoretical model is described for the interaction between isotopes of hydrogen and the eutectic PbLi sample considering the particular boundary conditions for the absorption and desorption processes. This model has been specifically developed for the upgraded Absorption-Desorption facility available at the UPV/EHU, according to the new configuration of the experimental chamber made of glass and quartz and the geometry of the crucible made of tungsten that is designed to hold the PbLi sample. Three different phases are described (loading, pumping, and release) together with the boundary conditions that have been taken into account in each one. This way, different mathematical expressions for the concentration profile of the isotopes of hydrogen through the PbLi sample are posed for each phase so that the experimental measurements to be carried out in the upgraded Absorption-Desorption facility will be fitted to them, and as a result, the transport parameters will be obtained.