Trapping performance of alkali-activated materials incorporating a hydrogen/tritium getter for the conditioning of tritiated organic liquids

Abstract

In this research, novel alkali-activated materials (AAM) are assessed for the conditioning of tritiated organic liquids OL. Their originality is to ensure both the conditioning of radioactive OL waste and the trapping of hydrogen or tritium (1H2 or 3H2). Two types of AAM are compared, either based on metakaolin MK (i.e., on geopolymer GEO solid structure) or on blast furnace slag BFS (i.e., Portland cement solid structure). For the trapping of 1H2 or 3H2, both AAM incorporate a γ-MnO2/Ag2O getter powder at 10 wt.%.The efficiency of 1H2 trapping in the two AAM is quantified via in situ 1H2 production, using two distinct methods: (1) gamma irradiation (short term 1H2 production) and (2) magnesium metal Mg corrosion (longer term 1H2 production). Complementarily, the 1H2 trapping efficiency of the getter is analyzed in both AAM porewaters.Gamma irradiation with a cumulated dose up to 500 kGy shows that GEO-based AAM added with getter have a H2 trapping efficiency of almost 100% without OL, and 87–92% with OL, when compared to identical materials made with non-trapping γ-MnO2. BFS-based AAM made with getter have a trapping efficiency of 52–65% without OL and 16–25% with OL.After 443–464 days of Mg corrosion, the cumulated amount of 1H2 trapped in BFS AAM reaches an asymptote of 0.7 mmol/g of getter, but it keeps increasing in GEO AAM. This proves the excellent 1H2 trapping efficiency of getter-functionalized GEO, compared to BFS AAM.Finally, the contact of the getter with the extracted porewaters of the two AAM shows a strong adsorption of ions on its surface. In both AAM, this reduces the 1H2 trapping capacity by 50%. When the getter is placed in contact with sulfides, which are present in BFS AAM only, X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) evidence that the structure of the getter is modified. This explains the limited 1H2 trapping efficiency of the getter in BFS AAM, whereas the getter-functionalized GEO AAM remains efficient.