Static glass leaching tests were conducted with three inactive reference glasses (French AREVA SON68 glass, SM513 PAMELA glass and the International Simplified Glass (ISG)) at 30�C and 70�C under inert atmosphere in contact with alkaline solutions at a high ratio of glass surface area to solution volume in order to determine the glass dissolution rates and the glass dissolution mechanisms. The final glass dissolution rates were lower than the initial ones. The causes of the rate decrease depends on the considered glass and medium. Presumed causes are an affinity effect (pseudo-equilibrium between the solution and the glass or the alteration layer), a pH decrease by secondary phase formation and a protection by the alteration layers formed. Alteration layers were characterized by SEM-EDX showing the presence of modified alkali-silica gels or modified C-S-H with a low Ca/Si ratio. In this study, the positive Ca effect was also highlighted especially by comparing tests performed in a KOH solution without Ca and those in OCW containing Ca. XRD analyses on altered glass samples at 70�C have allowed the identification of zeolites which can destabilize the alteration layers by consuming its constitutive elements (mainly Si and Al). According to geochemical modelling, such phases are suggested to be formed also at 30�C, which could explain the constant relatively high final dissolution rate.
|State||Published - 21 Aug 2017|
|Publisher||Studiecentrum voor Kernenergie|