Abstract
Uranium encapsulated in grout was exposed to water vapour for extended periods of time. Through synchrotron x-ray powder diffraction and tomography measurements, uranium dioxide was determined the dominant corrosion product over a 50-week time period. The oxide growth rate initiated rapidly, with rates comparable to the U + H2O reaction. Over time, the reaction rate decreased and eventually plateaued to a rate similar to the U + H2O + O2 reaction. This behaviour was not attributed to oxygen ingress, but instead the decreasing permeability of the grout, limiting oxidising species access to the metal surface.
Highlights
In the UK, Intermediate Level nuclear Waste (ILW) canisters contain primarily uranium, aluminium and Magnox alloy swarf encapsulated in a high alkaline grout within a stainless steel container
The aim of our study was to examine the corrosion behaviour of as-received and nitric acid etched uranium metal encapsulated in Blast Furnace Slag (BFS):Ordinary Portland Cement (OPC) grout when exposed to water vapour over a 50 week time period
These conditions were chosen to reflect the environmental conditions found in dry interim storage, and the results provide important information such as the dominant types and rates of uranium corrosion which could be used for predictive corrosion modelling of ILW containers
Summary
In the UK, Intermediate Level nuclear Waste (ILW) canisters contain primarily uranium, aluminium and Magnox alloy swarf encapsulated in a high alkaline grout (pH 10–13) within a stainless steel container. The uranium metal surface may be pre-corroded, exhibiting a thick oxide layer, or, if it is grouted immediately after de-canning from the Magnox cladding, it may retain a fresh metallic surface with limited oxide development. These containers are in dry storage at Sellafield for up to 30 years, where the temperature is generally regulated. Establishing a risk assessment and quantitative analysis of metal corrosion hidden within grout and stainless steel poses a significant challenge
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