Year-end Sale % OFF 
Abstract
The French concept developed to dispose high-level radioactive waste in geological repository relies on glassy waste forms, isolated from the claystone host rock by steel containers. Understanding interactions between glass and surrounding materials is key for assessing the performance of a such system. Here, isotopically tagged SON68 glass, steel and claystone were studied through an integrated mockup conducted at 50 °C for 2.5 years. Post-mortem analyses were performed from nanometric to millimetric scales using TEM, STXM, ToF-SIMS and SEM techniques. The glass alteration layer consisted of a crystallized Fe-rich smectite mineral, close to nontronite, supporting a dissolution/reprecipitation controlling mechanism for glass alteration. The mean glass dissolution rate ranged between 1.6 × 10−2 g m−2 d−1 to 3.0 × 10−2 g m−2 d−1, a value only 3–5 times lower than the initial dissolution rate. Thermodynamic calculations highlighted a competition between nontronite and protective gel, explaining why in the present conditions the formation of a protective layer is prevented.
Highlights
In France, like in the other countries using nuclear power plants, plans for disposing high-level radioactive waste (HLW) in a deep geological repository are being developed
We demonstrate that Fe from the iron piece reacted with Si from the glass to form nontronite, leading to a high glass dissolution rate and a low dispersion of Si released by the glass
Transmission Electron Microscopy (TEM) with Energy Dispersive Spectroscopy (TEM-EDS) analyses (Fig. 3a, b and c) show that the i-GAL consists of a stack of thin alteration layers of 0.2 μm, which are composed of foliated aggregates (Fig. 3c) compatible with the poorly-ordered smectite morphology[44]
Summary
In France, like in the other countries using nuclear power plants, plans for disposing high-level radioactive waste (HLW) in a deep geological repository are being developed. A few studies have focused on glass alteration mechanisms following Si migration in isotopic 29Si leaching experiments and secondary ion mass spectrometry (SIMS) 29Si/28Si ratio detection[30,32,33] They observed that the gel had a 29Si/28Si ratio intermediate between glass and solution, and an outer phyllosilicate-rich layer with a 29Si/28Si ratio close to the one detected in solution, clear evidence that the hydrolysis/condensation or dissolution/reprecipitation can take place simultaneously. Transmission Electron Microscopy (TEM) with Energy Dispersive Spectroscopy (TEM-EDS) analyses (Fig. 3a, b and c) show that the i-GAL consists of a stack of thin alteration layers of 0.2 μm (total 1–1.5 μm thickness), which are composed of foliated aggregates (Fig. 3c) compatible with the poorly-ordered smectite morphology[44]. This value is compatible with partially dehydrated smectites[46,47,48], whose reticular distance could be modified through the freeze-drying preparation process
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
