Simulation of Self-Irradiation of High-Sodium Content Nuclear Waste Glasses

Abstract

Alkali-borosilicate glasses are widely used in nuclear industry as a matrix for immobilisation of hazardous radioactive wastes. Durability or corrosion resistance of these glasses is one of key parameters in waste storage and disposal safety. It is influenced by many factors such as composition of glass and surrounding media, temperature, time and so on. As these glasses contain radioactive elements most of their properties including corrosion resistance are also impacted by self-irradiation.The effect of external gamma-irradiation on the short-term (up to 27 days) dissolution of waste borosilicate glasses at moderate temperatures (30¢X to 60¢XC) was studied. The glasses studied were Magnox Waste glass used for immobilisation of HLW in UK, and K-26 glass used in Russia for ILW immobilisation. Glass samples were irradiated under ×-source (Co-60) up to doses 1 and 11 MGy. Normalised rates of elemental release and activation energy of release were measured for Na, Li, Ca, Mg, B, Si and Mo before and after irradiation. Irradiation up to 1 MGy results in increase of leaching rate of almost all elements from both MW and K-26 with the exception of Na release from MW glass. Further irradiation up to a dose of 11 MGy leads to the decrease of elemental release rates to nearly initial value. Another effect of irradiation is increase of activation energies of elemental release.

Topologically disordered systems at the glass transition

“…Defect entropy plays an important role in crystalline materials due to the high entropy values and carrier concentrations and their high mobility in ionic conductors [34,35]. We evaluate both H d and S d from experimentally measured viscosity data of amorphous materials based on Doremus' model of viscosity which relates the viscosity of net-forming materials to thermodynamic parameters of network defects [22][23][24].…”

“…This equation can be fitted to practically all available experimental data on viscosities of amorphous materials [23,24]. Moreover equation (3) can be readily approximated within a narrow temperature interval by known empirical and theoretical models such as Vogel-Fulcher-Tamman, Adam-Gibbs, or Kohlrausch type stretch-exponential law [22,36,37].…”

“…Finally, as is known from percolation theory when the concentration of configurons exceeds the threshold level they form a macroscopic so-called percolation cluster, which penetrates the whole volume of the disordered network [26,42]. As configurons are moving in the disordered network the percolation cluster made of broken bonds is a dynamic structure which changes its configuration remaining however an infinite percolation cluster [24]. The percolation cluster is made entirely of broken bonds and hence is readily available for a more percolative than a site-to-site diffusive motion of configurons.…”

“…We used for numerical analysis two binary systems: amorphous silica and germania as the simplest glass forming materials. Thermodynamic data for broken bonds were evaluated based on recent results on the viscosity of amorphous materials treated theoretically by use of Doremus' defect model of viscosity [22][23][24]. This model relates the viscosity of an amorphous material to the concentration of broken bonds (defects) which are believed to be responsible for the viscous flow [22].…”

Glassy Wasteforms for Nuclear Waste Immobilization

“…[71] Similar effects were observed in irradiated phosphate glasses. [16] Summarizing the data available leads to the conclusion [72] that the irradiation had a detectable and even significant impact in cases when corrosion occurred via diffusion-controlled ion exchange. These conditions are characterized by relatively low temperatures (£323 K [50°C]), low and medium pH (£8), relatively high absorbed doses ( ‡6 10 6 Gy), and for diluted solutions over short corrosion times (t £ s(T)).…”