Structural investigation of borosilicate glasses containing lanthanide ions

Abstract 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.