![]() ![]() In the present investigation, this glass matrix was mixed with three different lanthanide oxides i.e. The 55SiO 2♱0B 2O 3♲5Na 2O♵BaO♵ZrO 2 (mol%) glass matrix was earlier synthesized and its structural properties were reported 8. In this paper, the structure of borosilicate glasses, incorporated with lanthanide oxides CeO 2, Nd 2O 3 and Eu 2O 3, and their effects were investigated on the structural properties of the glass network. Among the lanthanide ions Ce 3+ can be used to model Pu 3+, while Nd 3+ and Eu 3+ to model trivalent actinides, in particular Cm 3+ and Am 3+, respectively, considering their very similar ionic radii 7. Note, that Ce is easier to reduce to its trivalent state at higher preparation temperatures, leading to both Ce 3+ and Ce 4+ ions 6. Since handling high activity radioactive actinides is not permitted in standard laboratory environments, studies are commonly performed using lanthanides (Ce 3+, Nd 3+ and Eu 3+) as non-radioactive surrogates for the actinides, due to their very similar chemical properties 5, 6. Improved waste immobilizer borosilicate glass compositions must exhibit excellent chemical durability, higher glass transformation temperature than those currently used. Basic and applied research is conducted world-wide to model the effects upon incorporation of such radioactive chemical constituents in their structure, determine solubility limits, study chemical durability and temperature stability of the candidate host materials. The borosilicate glasses, due to their mechanical and chemical durability, are widely accepted as candidates for immobilization HLW materials 2, 3, 4. After reprocessing radioactive long-lived actinide elements, such as Th, U, Np, Pu, Am and Cm 1 were identified which need treatment and long term storage in an inert host material. During reprocessing U and Pu are converted into a Mixed Oxide material, which can then be recycled as nuclear fuel. High-level radioactive wastes (HLW) are produced by reprocessing spent nuclear fuel, which contains approximately 95% uranium, up to 1% Pu, up to 4% other actinides and various fission products. This effect is of particular importance from the point of view of chemical durability of a glass. These properties, however, are considerably modified by the network modifiers, which exist as single ions amongst the cross-linked network (of Si-O-B in borosilicate glasses) reducing the relative number of strong bonds leading to lower melting point, lower viscosity and modified thermal and electrical properties. Second neighbour atomic pair correlations reveal Ce, Nd, Eu to be accommodated in both Si and B sites, supporting that the borosilicate-matrix well incorporates Ln-ions and is likely to similarly incorporate actinides, opening a way to radioactive nuclear waste immobilization of this group of elements in a borosilicate glass matrix.Ī plethora of the useful glass properties stem from those of the network formers which constitute the bulk of the glass. Raman spectra, in full agreement with neutron diffraction, confirm that the basic network structure consists of BO 3/trigonal and SiO 4/BO 4 tetrahedral units. ![]() Ln-addition promote the BO 3 + O -→ – isomerization resulting in lower fraction of boron in BO 3, as compared to BO 4 units. ![]() 11B Magic Angle Spinning Nuclear Magnetic Resonance is indicative of simultaneous presence of trigonal BO 3 and tetrahedral BO 4 units, with spectral fractions strongly dependent on the Ln addition. ![]() Neutron diffraction combined with of Reverse Monte Carlo simulations show that all investigated glass structures comprise tetrahedral SiO 4, trigonal BO 3 and tetrahedral BO 4 units, forming mixed Si-O- B and Si-O- B linkages. Here we present structural studies of a simplified glass-matrix, − 55SiO 2♱0B 2O 3♲5Na 2O♵BaO♵ZrO 2 - upon adding lanthanide (Ln-)oxides: CeO 2, Nd 2O 3, Eu 2O 3, in two different concentrations 10% and 30w% each, to investigate the effects of lanthanides (Ln) taken as chemical surrogates for actinides. Understanding the effects of actinide addition to a borosilicate glass matrix is of great importance in view of waste immobilization. Borosilicate glasses are of great potential amongst the candidates of suitable inert materials for radioactive waste immobilization. High level radioactive actinides are produced as a side product in reprocessing spent nuclear fuel, for which safe long-term-inert immobilizer matrices are needed. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |