New nuclear glass-ceramics are extensively studied for the radioactive waste confinement, due to the double confinement conferred by the glass-ceramics. In this study, a glass-ceramic constituted by an aluminosilicate glass in the system: SiO2-Al2O3-CaO-MgOZrO2-TiO2, containing 2wt.% of Ca0.83Ce0.17ZrTi1.66Al0.34O7 zirconolite, has been synthesized by the discontinuous method. Cerium, an actinide surrogate is introduced both in the glass and ceramic phases. The synthesis is performed by a double melting at 1350?C, followed by a nucleation at 564?C, during 2 h, and a crystal growth at 1010?C during 3 h. Then effect of Ca/Mg ratio on the distribution of the crystalline network in the material was studied for Ca / Mg ratios ranging from 0.4 to 5.5. For the whole of the materials, Archimedes density is about 2.80 g/cm3. X-ray diffraction (XRD) analysis shows that the increase of Ca/Mg ratio leads to the increase of aluminosilicated crystalline phases with high Ca contents; the materials molar volumes remaining constant. The zirconolite phase is not affected by these additive aluminosilicated phases. The scanning electron microscopy analysis (SEM) coupled with energy dispersive X-ray (EDX) analysis confirmed these results; and shows the uniformity of distribution of the ceramics in the bulk of the materials.

This study investigates the effect of crystallization time (tc) in the structure of an iron-rich glass-ceramic (GC) dedicated for high-level radioactive waste (HLW), ceramized by nucleation–crystallization treatment at 790 °C for 2 h and 950 °C, for different periods ranging from 3 to 12 h. Density, XRD, SEM, FTIR, and Microwave chemical durability results are shown. Considering all the materials, Archimedes' density is between 2.607 and 2.634 g/cm3. Both XRD and SEM analyses revealed the development of two main crystalline phases, spodumene (LiAlSi2O6) and (Zr, Ln) molybdate La2Zr3(MoO4)9, during the heat treatment. These phases regularly grow by the increase of crystallization time. They are known as radionuclides' sequestration minerals. FTIR analysis confirms the complex GCs chemical composition. The microwave chemical durability test performed on GCs crystallized at tc = 9 h was conducted to evaluate their chemical stability. The leachates of the elements: Al, Fe, Mg, Li, Mo, Na, Si, and Zr were analyzed by ICP-OES. RLi values of Al, Mg, Mo, and Zr elements representing the radioactive waste (RW), vary between 2.3218x10-8 and 2.9204x10-8 kg/m2d. For Fe and Li, were slightly lower. However, RLSi was highest reaching 1.7457x10-6 kg/m2d. The elementary percentages extracted during the dissolution test for all elements are less than 0.5 %, which makes our material chemically stable. Its resistance to such an aggressive dissolution test makes it a good candidate for the confinement of some RW elements.

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Many glass ceramics are potential candidates for the confinement of radioactive waste. This is the case of glasses embedding radiation-resistant ceramics as zirconolites, pyrochlores or pyroxenes. This study deals with the influence of the crystal growth temperature on the formation of such phases in a nuclear glass ceramic in the system: Al 2 O 3 -SiO 2 -CaO-MgO-ZrO 2 -TiO 2 . The materials with six contents of ZrO 2 , ranging from 1.00 to 6.40 m.%, are synthesized by a discontinuous method, consisting in a double-melting at 1,350 °C, followed by both a nucleation at 564 °C, and a crystal growth treatment at: 900, 100 and 1,100 °C. For the whole of the materials, the morphology reveals a glassy feature, with a opaque aspect. One can also evidence a different crystallization process from the bulk to the surface. The glass ceramics X-ray diffraction analysis (XRD) show that the main identified crystalline skeletons are those of: 2M-zirconolite, CaZrTi 2 O 7 and ZrO 2 , depending on the content of ZrO 2 in materials and the crystal-growth temperature. The material with the middle content in ZrO 2 (4.5 m.%) and crystallized at the middle value of Tc (1,010 °C) show the greatest content in zirconolite (87 %), doped with either lanthanides or alcalin-earth elements, due to the complexity of the mixture of oxides. The temperature of 1,010 ° C appears to be more selective with regard to the formation of the 2M-zirconolite.

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