Resolving Reaction Mechanisms, Kinetics and Mass Transport in Radionuclide-Loaded Geopolymer Cement Wasteforms

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In the UK, over 150,000m of radioactive waste (enough to fill 60 Olympic size swimming pools) has been produced to date. Most of this radioactive waste needs conditioning, by either encapsulating it in cement, or another method, prevent release to the biosphere. Geopolymer cements are attractive for cementation of radioactive waste due to enhanced chemical resistance in aggressive environments, enhanced chemical tolerance to problematic wastes, higher fluidity of preparation leading to higher waste loadings, and cation-binding sites that provide enhanced capture of radioactive waste.Geopolymers have demonstrated lower leach rates of fission product surrogates than other encapsulant alternatives and this may be used to justify greater waste loading or disposal of boundary wastes to lower repository ratings. However, there is little information on what parameters of raw materials are critical to reliable application, under such conditions required on nuclear encapsulation plants.This project aims to provides greater understanding of geopolymer reaction, setting and hardening, by investigating fundamental particle interactions, so that robust specifications can be developed, and geopolymer wasteform properties and performance can be predicted. The project also aims to assess mobility of fission products, and establish chemical durability and radioactive waste retention.Specifically, it will:1. Characterise geopolymer wasteform phase assemblage, micro- and nanostructure, and structure of the pore network.2. Investigate fundamental particle interactions so that robust specifications can be developed.3. Determine radionuclide (e.g. 90Sr and 137Cs)-cement interactions.4. Assess radionuclide retention. This will identify key interactions controlling phase evolution, structural evolution across micro, nano and atomic length scales, radionuclide-cement interactions mass transport mechanisms and leaching resistance, and physical and chemical stability in repository relevant conditions.