Thesis
The impact of high temperatures on suitability of NRVB cement in nuclear waste management
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2026
- Thesis identifier
- T18228
- Person Identifier (Local)
- 202170449
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- This thesis investigates the effect of elevated curing temperatures on Nirex Reference Vault Backfill (NRVB) cement, a candidate backfill material for use within the United Kingdom’s Geological Disposal Facility (GDF). NRVB provides a highly alkaline environment, decreases radionuclide solubility, and provides a permeable pathway for gas transport. However, the thermal output of radioactive waste can alter the mineralogical and microstructural properties of the cement, which may impact its long-term performance and safety functions. The long-term performance of NRVB cement cured under the thermal conditions associated with radioactive waste disposal is poorly understood, particularly at curing temperatures above those previously studied. This thesis characterises mineralogical evolution, pore structure development, and radionuclide sorption behaviour. A multi-technique approach was used. X-ray diffraction (XRD) was used to identify and quantify mineral phases, with method development undertaken to minimise carbonation during sample preparation and analysis. Scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) were used to examine microstructural and chemical changes. X-ray computed tomography (XCT) and helium pycnometry were used to quantify porosity. Radionuclide sorption experiments were performed to assess the influence of temperature-induced mineralogical changes on radionuclide retention. The results demonstrate a direct relationship between curing temperature, mineralogical evolution, and porosity. Elevated temperatures promoted the formation of strength-reducing mineral phases and resulted in increased porosity. Curing temperature and calcium-to-silica (C:S) ratio controlled the mineralogy. The mineral composition was also shown to influence radionuclide immobilisation mechanisms, with different mineral phases exhibiting different radionuclide interaction pathways and pH buffering capacities. These findings demonstrate that the long-term performance of NRVB cement depends on both its mineralogical and microstructural evolution, which are controlled by curing temperature and cement composition. The work provides new insights into the behaviour of higher-temperature NRVB cements and contributes novel data on the formation of high-temperature cement minerals and their interactions with radionuclides.
- Advisor / supervisor
- Stillings, Mark
- Dobson, Katherine
- Resource Type
- DOI
- Funder
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