Establishing technical specifications for PbLi eutectic alloy analysis and its relevance in fusion applications

One of the key aspects on the future operation of liquid metal-based breeding blankets is the eutectic composition of the lead–lithium (PbLi) alloy. There is discrepancy on the exact eutectic point, varying the lithium content from 15 at% to 17 at%, which will be discussed in this work. Additionally, the PbLi to be used during the R&D activities requires a careful characterization. A guide that compiles a detailed description of the material handling, analytical techniques to be applied and results interpretation is presented for an improved use of this alloy in experimental fusion applications. Some of the employed techniques are thermogravimetry, inductively coupled plasma mass spectrometry and X-ray diffraction, among others. In CIEMAT, PbLi samples from different providers have been analyzed showing a lithium dispersion from 3 at% to 18 at% and with an impurity content up to 400 ppm. The exact lithium content and the presence of impurities have a high impact on the experimental activities in support to PbLi related technologies. A crucial point is how it affects neutronic calculations on the Tritium Breeding Ratio. In addition, it is reported a bibliographic review denoting the existence of a large experimental uncertainty in the solubility values for hydrogen isotopes in PbLi. It is known the higher solubility of hydrogen in lithium against lead, therefore small deviations on the lithium percentage may imply an inaccuracy on those values. This reasoning can be also applied on the experimental determination of the diffusivity values.