دانلود رایگان مقاله انگلیسی مطالعه جنبشی و تکامل ساختاری هسته زباله شیشه ای SON68 تغییر یافته - الزویر 2018

Abstract

The French reference SON68 nuclear waste glass corrosion under H2O and D2O 18 atmosphere was investigated at 35−125 °C and different relative humidities (92 - 99.9%). The hydration kinetic was followed by FTIR and solid characterization was achieved using SEM/EDX, Raman and TOF-SIMS. The water diffusion coefficients in the glass ranged from 8.7  10-22 to 5.3  10-19 m2 s -1 . The alteration products were calcite, apatite, powellite and tobermorite. Pre-hydrated glass alteration in synthetic groundwater at 50 °C showed an instantaneous release of elements from the surface, making it important to evaluate well the vapour hydration period of the glass.

Conclusion

We investigated the vapour hydration of the SON68 glass under different conditions of temperature (35‒125 °C) and relative humidity (92‒99.9%) relevant to high-level waste geological disposal in France. The glass hydration increased with increasing time, temperature and relative humidity. Measurements of hydration thicknesses using 3 different techniques, SEM, FTIR and TOF-SIMS, allowed calculating a glass hydration activation between 34 (±4) and 68 kJ mol-1 , consistent with a diffusion and chemical reaction processes. The water diffusion coefficient at 90 °C and 95% RH, 7.5  10-20 m2 s -1 , is 350 times higher than that reported by Ferrand et al. [22] (2  10-22 m2 s -1 ) for the SON68 glass altered at 90 °C in a Sisaturated (240 ppm) synthetic solution.

In the presence of D2O 18 (20 %), the incorporation of 18O in the alteration layer revealed two mechanisms responsible for the glass alteration. The formation of phyllosilicates occurs by a dissolution/ precipitation process from the supersaturation of the bulk solution while the gel is formed by a succession of very local hydrolysis/condensation reactions (away from the bulk solution). The apparent diffusion coefficient of D2O 18 is about 2.3  10-19 m2 s -1 . The alteration in COx water of pre-hydrated glass samples showed the instantaneous release of glass tracer elements, much faster than for the non-hydrated glass sample. The phenomenon is due to an instantaneous dissolution of fast-dissolving phases (e.g. salts) incorporated in the hydrated layer.

Finally, in the context of geological disposal of HLW it is important to evaluate the water under-saturation period to better assess the radionuclides release in the groundwater contacting the hydrated glass.