Xenotime as a material for actinides specific storage – x-mas
Phosphate ceramics as a specific matrix for the conditioning of actinides: the case of xenotime.
The main objectives of the XMAS project were reached. We mounted and fully characterized new compounds belonging the xenotime family. Then, we studied their thermal stability, resistance to irradiation and also their chemical durability (thermodynamics and kinetics). Therefore, we added a new credible candidate for the management of radioactive wastes.
From the synthesis to the evaluation of the ceramic behavior under irradiation and chemical stress: towards optimal conditioning of actinides.
Nuclear energy appears as an important actor to supply clean and sustainable electricity with low carbon dioxide emission. One of the main challenges facing this industry is related to the conditioning and storage of the generated radwastes. In this framework, ceramic “crystalline” matrices especially phosphates appeared as promising candidates for the specific conditioning of actinides.1-3 Such interests stem not only from their easy way of fabrication, but also to their good resistance to radiation damage, interesting sintering capability and very high chemical durability. Moreover, the use of such matrices dedicated to specific conditioning allows the incorporation of higher actinide loadings compared to other matrices, which will decrease significantly the volume of the package to store. During the XMAS project, we paid a particular attention to the potential use of the xenotime structure (Zircon structure type, I41/amd). A library of new compounds with a general formula of CayAn(III,IV)y+1-xLnx+(1-2y)(SiO4)1-x(PO4)x.nH2O were synthesized, sintered and their resistance to irradiation were studied as well as their chemical durability giving access to their thermodynamic and kinetics parameters.
A library of different compounds was synthesized by following different protocols (precipitation and hydrothermal) that we developed at the ICSM. A multiparametric approach was carried out by varying different parameters such as pH, temperature, duration, stoichiometry of reactants. As a result, we obtained for the first time different composition (Th,U)1-xErx(SiO4)1-x(PO4)x, Cax(Th,U)xEr1-2xPO4, (Th, U)xEr1-xPO4. All these materials crystallize in the xenotime structure in the zircon structure type (tetragonal, I41/amd). All these materials were subject to a thorough characterization by using different techniques such as by PXRD, SEM-TEM, ICP. Moreover, the low temperature precursor with a general formal of LnPO4.2H2O (Ln= Gd-Lu) were obtained in the gypsum structure type and converted into pure xenotime around 300°C. Thermal behavior of the obtained compounds was studied showing a good stability up to 1600°C. High dense pellets of ErPO4 (up to 96%) were subject to irradiation experiment under different conditions and dissolution experiments were carried out too.
- Synthesis of pure Th1-xErx(SiO4)1-x(PO4)x and for the first time of U1-xErx(SiO4)1-x(PO4)x
- Synthesis of CaxAnxEr1-2xPO4 and AnxEr1-xPO4.
- Synthesis of LnPO4.2H2O with Ln = Gd-Lu
- External irradiations (dual and single beam irradiation)of ErPO4 densified pellets
- Thermodynamics study of Th1-xErx(SiO4)1-x(PO4)x and LnPO4.2H2O
- Determination of the dissolution rate of the Th1-xErx(SiO4)1-x(PO4)x compounds
- Determination of the magnetic properties of LnPO4.2H2O with Ln = Gd-Lu
The majority of the objectives of the XMAS project are considered as reached. We reported new set of data towards the use of the xenotime ceramics. Major advances were made by developing new formulation of ceramics belonging to the phosphates, we evaluated successfully their results to irradiation and to dissolution also. The obtained results represent a new contribution to the list of a candidates destined to the management of the nuclear wastes. The obtained results finds application in the radiochemistry field as well as in geology and for diverse materials science applications. Compared to the existing ceramics, the XMAS project initiated the exploration of xenotime materials, but many aspects need to be considered and studied in details such as a thorough sintering and dissolution study. It is worth noting that during the last four years of the XMAS project, we initiated and developed many national and international collaborations. Irradiation experiment were performed in collaboration with Anne Magali Seydoux-Guillaume (Saint-Etienne), and thermodynamics results were obtained in collaboration with Alexandra Navrotsky (ASU, USA). In addition, we went beyond the main objectives of the XMAS project by studying the magnetic properties of the churchite phases in collaboration with Robert Cava from Princeton university, USA. The results of the XMAS project are also part of the INWARD (Ion Beam Irradiation for High Level Nuclear Waste Form Development) collaborative research project managed by the IAEA.
1. Shelyug, A.; Rafiuddin, M. R.; Mesbah, A.; Clavier, N.; Szenknect, S.; Dacheux, N.; Guo, X.; Navrotsky, A., Effect of Annealing on Structural and Thermodynamic Properties of ThSiO4-ErPO4 Xenotime Solid Solution. Inorganic Chemistry 2021, 60 (16), 12020-12028.
2. Rafiuddin, M. R.; Seydoux-Guillaume, A. M.; Deschanels, X.; Mesbah, A.; Baumier, C.; Szenknect, S.; Dacheux, N., An in-situ electron microscopy study of dual ion-beam irradiated xenotime-type ErPO4. Journal of Nuclear Materials 2020, 539.
3. Subramani, T.; Rafiuddin, M. R.; Shelyug, A.; Ushakov, S.; Mesbah, A.; Clavier, N.; Qin, D.; Szenknect, S.; Elkaim, E.; Dacheux, N.; Navrotsky, A., Synthesis, Crystal Structure, and Enthalpies of Formation of Churchite-type REPO4·2H2O (RE = Gd to Lu) Materials. Crystal Growth & Design 2019, 19 (8), 4641-4649.
For safer and clean nuclear energy, X-MAS project intends to develop highly durable phosphate matrices dedicated to the long term storage of high level nuclear wastes. This project will consider the xenotime phase having a general formula of LnPO4 (Ln = Tb–Lu) and crystallizing in the zircon structure type. When considering trivalent actinides or their lanthanide surrogates, the incorporation goes through the formation of solid solutions of Ln1-xAnxPO4, whereas for tetravalent actinides (Th, U), two different mechanisms will be explored leading to the formation of CaxAnxLn1-2xPO4 and AnxLn1-x(SiO4)x(PO4)1-x solid solutions. For the first time, such materials will be synthesized by wet chemistry routes allowing the formation of pure and homogeneous phases and will be thoroughly characterized. Afterward, their thermal behavior, sintering capability and their chemical durability will be evaluated in order to propose efficient matrices for the conditioning of high-level nuclear wastes.
Project coordination
adel mesbah (Institut de Chimie Séparative de Marcoule)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
Partnership
ICSM Institut de Chimie Séparative de Marcoule
Help of the ANR 225,590 euros
Beginning and duration of the scientific project:
November 2017
- 36 Months
