Growth Rate of Alteration Layer and Elemental Mass Losses During Leaching of Borosilicate Nuclear Waste Glass

Abstract

ABSTRACTMCC-1 static leaching experiments were carried out for a simulated waste glass in deionized water for up to 364 days at 90°C in order to examine the relationship between alteration layer thickness and elemental mass losses. The thickness of the layer increased linearly at a rate of 0.63,μm/day for the first 91 days, and thereafter it remained constant (about 60 μm) independent of time. The change in normalized elemental mass losses of B, Na, and Si with time shows the same trend as that of the change in the layer thickness. It is also demonstrated that the growth rate of the layer can be calculated from the released boron in the leachates. The shrinkage of the alteration layer during air-drying is not significant in spite of the porous structure of the layer, which results from the depletion of cations and the recrystallization reported previously. Although the apparent release of elements almost ceases after a 91-day leaching experiment, reactions in the layer such as crystal growth continue.