Developing technology and specifications for metakaolin-based geopolymers as robust and promising stabilisers for fuel debris removal

Past and ongoing decommissioning and cleanup operations at both the TEPCO Fukushima Daiichi Nuclear Power Plant and Sellafield site has generated significant quantities of complex radioactive waste streams. This includes solid fuel debris waste fragments comprising mainly molten core concrete interaction products, which include a variety of materials such as metallic alloys, oxides, and silicates, and slurries and sediments containing fine particles or colloids, which are variously rich in metal carbonates, ferric oxide, and/or barium sulphate.

New solidification and stabilisation methods are therefore urgently required to enable safe disposal of these waste streams.

This project will use calcined clays as natural resources to engineer geopolymer binders, with and without boron as a neutron absorbent, to provide a robust and future-proof waste cementation matrix for long-term management and disposal of degraded fuels and contaminated wastes in Japan and the UK. This will broaden the formulation envelopes to increase waste loading and compatibility with wastes that cannot be effectively treated by conventional cementation.

Geopolymer cements are produced via the chemical reaction between a source of alkalis (the "activator"), which is usually supplied as an aqueous solution, and a "precursor" powder that supplies silicate and aluminate for the reaction process. Geopolymer cements have been highlighted in technical and road-mapping publications in both the UK and Japan as offering very high potential for use in the treatment and disposal of diverse and problematic wastes.

In particular, geopolymer production using calcined clays as the main precursor has been identified as offering the possibility for excellent technical performance as a waste conditioning matrix, controllable in the fresh and hardened states, while removing the reliance of the nuclear sector on conventional cementitious powders that will become increasingly scarce in the coming decades.

We will identify and optimise geopolymer binder formulations that are robust to variations in the nature and characteristics of clay-derived and other precursors, including in terms of easy manufacturing (including desirable flow characteristics such as viscosity, yield stress, controlled thixotropy, and flow retention), radionuclide encapsulation (both cationic and anionic radionuclides), and encapsulation of complex waste streams such as solid waste fragments and slurries/sediments. This will underpin the use of geopolymers as a key part of the toolkit of cements that are needed to meet the remediation and decommissioning needs of the UK, Japan, and other countries worldwide.

The project has strong bilateral UK and Japan links, incorporating expertise from both universities and the Japan Atomic Energy Agency (Japan) and Sellafield Ltd. (UK).