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Title: Optimising blends of blast furnace slag for the immobilisation of nuclear waste
Author: Sanderson, Rebecca Anne
ISNI:       0000 0004 7651 8340
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2019
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The UK nuclear industry uses cement encapsulation as the preferred treatment option for intermediate level waste. The grout is a mix of Portland cement (10-25 wt. %) with blast furnace slag (75-90 wt. %) and is required to conform to strict performance criteria in order to achieve successful encapsulation. However, the supply of cement powder to the nuclear industry has been inconsistent, causing changes in the performance properties of the material over time. The supply of BFS changed from a unique powder specifically designed for the UK nuclear industry to a set of commercially available materials due to economic changes to the cement industry. A significant difference between the commercial material and the cement powders used historically, is the particle size. The particle size distributions of the commercial powders are much narrower and finer (higher specific surface area). This affects the rheology, fluidity, setting time, bleed and water demand of the cement grouts produced. In order to broaden the particle size distribution of blast furnace slag, a coarse and fine fraction with a similar chemical compositions were mixed together. By blending the two materials, it was possible to produce cement powder blends with a lower specific surface area that mimics the original specification powder. This research investigates the effect of altering the ratio of fine and coarse materials by monitoring the performance of the blast furnace slag in varying blends. The physical properties were monitored using fluidity, heat of hydration, setting time and the yield stress of the system. The ability of the cement pastes to infill around simulant nuclear waste was also determined using high resolution tomographic analysis. Large scale trials were also undertaken to simulate plant operations. The results found that each extreme of the blend (i.e. at 100 wt. % of either the finer or coarser material), the cement pastes do not conform to the required specification. This confirms the requirement for blending the two materials to produce the ideal particle size for the optimum performance. This will help future-proof the supply of cement powders to the nuclear industry.
Supervisor: Provis, John Sponsor: Not available
Qualification Name: Thesis (Eng.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available