Séminaire spécialisé

mardi 2 juillet 2013 à 16:00

Amphi G. Besse

Kinetic study and structural evolution of the French SON68 nuclear waste glass during vapor hydration and in silica saturated conditions

Rachid Bouakkaz

Subatech (groupe Radiochimie)

Three different experiments were carried out to measure the long-term residual dissolution rate of SON68 nuclear glass.
In the first part of this work, the glass monoliths and powder were hydrated at temperatures ranging from 35 to 125°C and various relative humidities (RH). Experiments were carried out in a stainless steel autoclave with a Teflon liner (40ml) placed in a 2 cm thick aluminium container to prevent temperature gradients that may cause vapour condensation on the glass samples during heating and cooling processes. 8 ml of liquid solution (water + NaCl) was used to ensure a constant RH by varying the NaCl concentration. Monoliths were removed from the autoclaves and analyzed using Fourier Transform Infrared (FTIR) spectroscopy. FTIR microscopy has shown that the rate of hydration is a function of the temperature and RH. The samples will examined by SEM, TEM, EDS, XPS and SIMS.
The second part studied the corrosion of glass monoliths and powder in dynamic mode (solution flow rate 3-5 ml/day) in silica saturated conditions at pH 8, glass surface-area-to-solution-volume (S/V) ratio near 14000 m-1 and at 35, 50 and 90°C. Diffusion-controlled process dominates the initial stage of glass dissolution at 90°C and throughout the leaching experiments at 35 and 50°C. Temperature accelerates the formation of a gel layer. After 653 days alteration the normalized leaching rates were 2.78×10-6, 6.4×10-6 and 1.57×10-4 respectively. The activation energy Ea was calculated using an Arrhenius relationship and compared to other literature results.
The last part concerned the alteration of 29Si-doped SON68 glass in the presence of Callovo-Oxfordian argilite and stainless steel P235GH to understand the effect of near field materials on the rate of glass dissolution and the migration of 29Si in the claystone core. Experiments were performed using percolation cells containing glass and stainless steel sandwiched between two clay cores in two different combinations. These combinations were glass/clay at 50 and 90°C, and glass/clay/steel at 90°C. COX water was forced through the percolation cells at 120 bars (solution flow rate 0.5-0.6 ml/day), (S/V) ratio is near 1,8×105 m-1. Chemical analysis have been performed by ICP-MS, HR-ICP-MS and ionic chromatography. The results have been compared to leaching experiments, which were conducted in dynamic mode with silica rich solution at 50 and 90°C.