In fusion technology, it is very important that PbLi will be produced according to nuclear materials QA (Quality Assurance) standards, because it has a major impact on PbLi properties as breeding blanket material. QA requirements for PbLi eutectic refers to its constitutive (accurate determination of Li content) and compositional (accurate determination of impurities content) characteristics. For this reason, it is necessary to perform an exhaustive control of the eutectic composition and purity of the PbLi alloy before, during and after each experimental campaign.
- O4.1 – Eutectic title of lead-lithium alloy Despite there is a large discrepancy on the exact eutectic composition, varying the lithium content from 15% to 17% atomic, it has been both experimentally and theoretically determined by statistical data that the eutectic title is at 84.3% at. lead (99.38% weight), together with 15.7% at. lithium
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(0.62% weight). In addition, the melting point for PbLi eutectic is 235 ℃, being the lowest one within the different Pb-Li compositions.
- O4.2 – Purity of the liquid metal Impurities in PbLi eutectic come, among others, from nuclear processes, corrosion reactions with structural and auxiliary materials and contamination with atmospheric gases. One of the first documents describing some requirements with respect to the maximum allowable impurity content in the production of PbLi alloy is EFDA document 05/998 “Procurement of the Pb-Li eutectic alloy for EBBTF facility and for dedicated neutronics experiment Annex A. Technical Specification”. In 2010, a group from IPUL (Institute of Physics, University of Latvia) produced PbLi eutectic alloy by MHD (magnetohydrodynamic) technology, fulfilling the chemical composition showed in Table 1. More recently, ITER corroborated these concentrations as the elemental composition for the lead-lithium eutectic alloy for tritium breeding blanket modules. These data are less restrictive than those presented in the EFDA document 05/998.
Table. Elemental composition of PbLi eutectic alloy recently published by ITER
| Element | Concentration (wppm) |
|---|---|
| Ag, Cu, Nb, Pd, Zn | < 10 |
| Cr, Fe, Mn, Ni, Pd, V | < 50 |
| Al, Si | < 100 |
| Bi, Sn, W | < 200 |
An exhaustive control of the purity of the PbLi alloy will be carried out before, during and after the experimental campaign.
As supporting theoretical study, the impact of the impurities on the activation level of the PbLi as radioactive waste (supposing its operational conditions in DEMO) will be also determined by activation calculations,
