A study of the Dissolution of UK Nuclear Waste Glass in Cement Waters

Within the United Kingdom (UK), it is proposed that nuclear waste will be disposed of in a geological facility, utilising an engineered barrier system that will be optimised to physically and chemically impede the transport of radionuclides to the biosphere. Understanding glass dissolution in environmental conditions designed to mimic geological disposal is paramount to the safety case of the UK’s radioactive waste disposal programme. Interaction of groundwater with the cementitious components of the facility will lead to the presence of high pH conditions within a disposal facility. The effect of such cement leachates on the durability of vitrified wasteforms is not well understood. The following body of work aims to address the concerns of nuclear waste glass in contact with cementitious materials. Here we present results from glass durability studies using simulated cement leachates and equilibrated cement water to elucidate the mechanisms that govern glass corrosion under these complex geochemical conditions. The normalised mass loss and normalised leaching rate as a function of cement leachate composition was determined by effluent solution analysis. Additionally, we present characterisation results collected on alteration layers by conducting x-ray diffraction and electron microscopy measurements on glass powders and monolith samples. Collectively, these data provide new insights into the mechanisms that govern glass dissolution in the complex geochemical conditions expected for vitrified UK waste if water breaches the engineered barrier system in a geological disposal facility. The work demonstrated in this thesis indicates that glass dissolution is less severe in cementitious leachates compared to pure water and young synthetic cement waters are more corrosive than evolved solutions with a lower concentration of alkali/alkaline earth ions.