The Role of Water Diffusion in the Corrosion of the French Nuclear Waste Glass SON 68 under Solution Saturation Conditions

Abstract

%675$&7The alteration kinetics of the French borosilicate glass SON 68 have been investigated in a dynamic system at 50°C and 90°C under solution saturation conditions. The pH was adjusted to 4.8, 7.2 and 9.8 with addition of chemical buffers or/and by bubbling CO 2 in solution. In all experiments, Li and Cs leaching seems to be controlled by a diffusion process. The Li-and Csconcentrations were used to calculate the sum of ionic exchange and matrix dissolution rates of the glass while Mo-concentrations indicate matrix dissolution. The final leaching rates in saturation condition of Mo were in the order of 10 -4 -10 -5 g.m -2 .d -1 in good agreement with those given in literature for static tests. The glass surface was studied by scanning and transmission electron microscopy (SEM, STEM) for analysis of the corrosion products and by infrared spectroscopy (FTIR) for water speciation and concentration. A good inverse correlation between the water content and the alkali concentrations released from the glass has been obtained. About three hydrogen ions replaced one alkali ion. Modeling of the experimental data using GM 2001 model gives water diffusion coefficients between 10 -20 and 10 -22 m 2 .s -1 .,1752'8&7,21 1 Mat. Res. Soc. Symp. Proc. Vol. 807

Corrosion of alkali–borosilicate waste glass K-26 in non-saturated conditions

“…Analysis of corroded glass profiles demonstrated that in Boom clay the corrosion of nuclear waste glasses is a diffusion controlled process [63]. Similar results have been obtained for French glasses SON68 in silica saturated conditions [68], moreover it has been shown that in such conditions the interdiffusion persists indefinitely and determines the actual rates of radionuclide releases [20]. Table 4 gives some values of the characteristic time s for a number of glasses in non-saturated conditions.…”

Mechanical Behavior of a Borosilicate Glass Under Aqueous Corrosion

“…The normalized glass leaching rate calculated from NL(Li) is 5 × 10 −11 kg/m 2 /s (4.5 × 10 −3 g/m 2 /d). This value is close to those obtained by Ferrand et al 3 . with SON68 glass powder corroded in a dynamic system.…”

“…The pH was adjusted to 9.7 by bubbling an Ar/CO 2 gas mixture. The solution composition is representative of the disposal conditions 3 . The corrosion experiments were conducted at 90°C in 50 mL Teflon containers (closed) for durations of up to 28 and 56 days.…”

“…Li is a corrosion tracer that indicates ionic exchange between alkalis from the glass and solution protons. The presence of Mo in the solution indicates the occurrence of glass matrix dissolution 3 …”

“…The solution composition is representative of the disposal conditions. 3 The corrosion experiments were conducted at 901C in 50 mL Teflon containers (closed) for durations of up to 28 and 56 days. The kinetics of glass corrosion were determined from the analysis of the solution by means of a mass spectrometer (PQ Excell, VG Elemental, Boston, MA) for lithium and molybdenum with a better than 3% accuracy.…”