NMR Investigation of Cation Distribution in HLW Wasteform Glass

Abstract

Magic-angle-spinning NMR has been used to establish the structural roles of various cations added to the borosilicate glass which is used for the vitrification of high-level nuclear waste (HLW). Representative surrogate oxides with nominal valencies of +1, +2 and +3 have been studied which span the range of oxides from modifier to intermediate and conditional glassformer. NMR has been carried out on those nuclei which are accessible and the species observed have been correlated with the physical and chemical behaviour. The controlling factor is the manner in which the alkali cations partition between the various network groups, changing the distribution of silicon Qn species and the boron N4 ratio. Identifiable superstructural units are also present in these glasses. The aqueous corrosion rate increases with Q3 content, as does the weight loss due to evaporation from the melt. The activation energy for DC conduction scales with N4. Values of N4 obtained for these glasses deviate significantly from those predicted by the currently accepted model (Dell and Bray) and are strongly affected by the modifier or intermediate nature of the surrogate oxide and also by its effect on the distribution of nonbridging oxygens between the silicate and borate polyhedra.

Durable Glass for Thousands of Years

“…[104] These results indicate that increasing the fraction of reedmergnerite or danburite c.r.s. in a glass should increase its durability.…”

“…99 NMR has indicated that glasses with more Q 3 than Q 4 silicate groups ww increase the dissolution rate of HLW glass. 103 The presence of Al, promotes Q 4 , reduces Q 3 , and reduces N 4 (the number of BO 4 tetrahedral groups). The presence of alkali and alkaline earth oxides increases Q 3 .…”

“…The presence of alkali and alkaline earth oxides increases Q 3 . 103 When considering these effects, the higher the fraction of albite CRS in a glass should increase its durability.…”

Infrared and Raman Spectroscopic Study of Glasses in the Al2O3-B2O3-Fe2O3-Na2O-SiO2 System

“…The structure of Al2O3-B2O3-Na2O-SiO2 glasses has been reported in the literature using nuclear magnetic resonance (NMR) and optical characterization techniques (see, for example [1,2]). The structure of Al2O3-B2O3-Na2O-SiO2 glasses has been reported in the literature using nuclear magnetic resonance (NMR) and optical characterization techniques (see, for example [1,2]).…”

Structural Characterization and Analysis of Glasses in the Al2O3-B2O3-Fe2O3-Na2O-SiO2 System

“…The structure of Al 2 O 3 -B 2 O 3 -Na 2 O-SiO 2 glasses has been reported in the literature using nuclear magnetic resonance (NMR) and optical characterization techniques [5,6]. The published work has been successful in identifying compositionally driven coordination changes in aluminum and boron, changes in the fraction of non-bridging oxygens, and the tendency for sodium to preferentially associate with aluminum.…”