Abstract
The International Simple Glass (ISG) is a six-component borosilicate glass which was developed as a reference for international collaborative studies on high level nuclear waste encapsulation. Its corrosion behaviour is typically examined when it is immersed in a leaching solution, or when it is exposed to water vapour. In this study, an alternative situation is considered in which the glass is only partially immersed for 7 weeks at a temperature of 90 °C. In this case, half of the glass sample is directly in the solution itself, and the other half is in contact with a water film formed by condensation of water vapour that evaporated from the solution. This results in a different degradation behaviour compared to standard tests in which the material is fully immersed. In particular, whilst in standard tests the system reaches a steady state with a very low alteration rate thanks to the formation of a protective gel layer, in partially-immersed tests this steady state could not be reached because of the continuous alteration from the condensate water film. The constant input of ions from the emerged part of the sample caused a supersaturation of the solution, which resulted in early precipitation of secondary crystalline phases.This setup mimics storage conditions once small amounts of water have entered a glass waste form containing canister. It offers a more realistic outlook of corrosion mechanisms happening in such situations than standard fully-immersed corrosion tests.
Highlights
Borosilicate and phosphate glasses are hosts for High Level and Intermediate Level nuclear Wastes (HLW, ILW) [1e3]; the preferred option for such waste forms being disposal in geological repositories
The International Simple Glass (ISG) used in this study dprovided by James Marra, Savannah River National Laboratory, USAd is a six-component borosilicate glass which was developed as a reference for international collaborative studies on high level nuclear waste encapsulation
We have demonstrated the different behaviour of ISG under partially-immersed conditions compared to standard fullyimmersed tests
Summary
Borosilicate and phosphate glasses are hosts for High Level and Intermediate Level nuclear Wastes (HLW, ILW) [1e3]; the preferred option for such waste forms being disposal in geological repositories. Other studies have already shown the limitations of extrapolating results from immersion tests to vapour tests [11,26] In this paper, another approach is undertaken in which the glass sample is only partially immersed in water during the experiment, in contrast with the more standard setups in which the sample is either completely immerged in water, or only in contact with water vapour. In this partial immersion test methodology, only half of the glass is immersed and the other half is exposed to water vapour (see Fig. 1) These experiments, by reproducing more closely the conditions in which water comes into contact with glassy waste forms, both in geological and near-surface repositories, give new insight into likely glass degradation mechanisms and highlight the importance taking into account partial immersion in long-term degradation of waste-glass containing canisters. Throughout the experiment, the pH was measured from solution samples brought to room temperature, using a Thermo Scientific Orion 3-star bench-top pH meter
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