The effect of blast-furnace slag particle size on the hydration of slag-Portland cement grouts at elevated temperatures

The UK nuclear industry has historically used a unique specification of cement powder that differs from construction industry requirements. However, the slags that complied with this specification have become unavailable. The material now used to meet the requirements of the specification is a blend of standard construction industry ground granulated blast-furnace slag (GGBS), which has high fineness, with Calumite which is a coarser slag powder. Both materials have very similar chemical compositions, and the main reason for blending is to control the particle size distribution (PSD) to replicate the performance of the previous supply. The effect of changing the PSD on the performance properties of the cement paste was investigated. Isothermal conduction calorimetry at elevated temperatures was carried out to monitor the heat of hydration; it was found that the peak heat and total heat evolution increased with an increase in GGBS content. It was also found that Calumite contributes very little to the hydration reaction and thus behaves similarly to an inert filler. As the GGBS content was decreased, the fluidity of the pastes increased up to a certain point, but decreased again for systems dominated by very coarse particles, indicating that there is an optimum balance between the finer and coarser slag particles within this cementing system

Characterisation and disposability assessment of multi-waste stream in-container vitrified products for higher activity radioactive waste

Materials from GeoMelt® In-Container Vitrification (ICV)™ of simulant UK nuclear wastes were characterised to understand the partitioning of elements, including inactive surrogates for radionuclide species of interest, within the heterogeneous products. Aqueous durability analysis was performed to assess the potential disposability of the resulting wasteforms. The vitrification trial aimed to immobilise a variety of simulant legacy waste streams representative of decommissioning operations in the UK, including plutonium contaminated material, Magnox sludges and ion-exchange materials, which were vitrified upon the addition of glass forming additives. Two trials with different wastes were characterised, with the resultant vitreous wasteforms comprising olivine and pyroxene crystalline minerals within glassy matrices. Plutonium surrogate elements were immobilised within the glassy fraction rather than partitioning into crystalline phases. All vitrified products exhibited comparable or improved durability to existing UK high level waste vitrified nuclear wasteforms over a 28 day period