Structural investigation of borosilicate glasses containing lanthanide ions

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. Borosilicate glasses are of great potential amongst the candidates of suitable inert materials for radioactive waste immobilization. Understanding the effects of actinide addition to a borosilicate glass matrix is of great importance in view of waste immobilization. Here we present structural studies of a simplified glass-matrix, − 55SiO(2)·10B(2)O(3)·25Na(2)O·5BaO·5ZrO(2) - upon adding lanthanide (Ln-)oxides: CeO(2), Nd(2)O(3), Eu(2)O(3), in two different concentrations 10% and 30w% each, to investigate the effects of lanthanides (Ln) taken as chemical surrogates for actinides. 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 ([4])Si-O-([3])B and ([4])Si-O-([4])B linkages. (11)B 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. Ln-addition promote the BO(3) + O(-)→[BO(4)](–) isomerization resulting in lower fraction of boron in BO(3), as compared to BO(4) units. 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. 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.