Materials for waste management

EAC research is centred on underpinning safe storage of spent fuel (wet/dry), storage and disposal of a wide range of nuclear waste streams, as well as the optimisation of overpacks and infrastructure for reprocessed product (THORP, the “100 year can”). Innovative applications of novel characterisation techniques and in-situ approaches are explored, towards providing a better understanding of the effect of storage conditions on material integrity.

Several research projects have been carried out to develop knowledge of material behaviour in chloride- and HCl containing atmospheres, to ensure long-term integrity of waste drums, containers, over-packs, and associated infrastructure. Variations in chemical species and concentrations, exposure temperature, the presence of organic compounds, and microstructure precipitation/welding/strain, relevant to modern manufacturing process, have been assessed. Deformation was found to induce higher EAC susceptibility, with bending deformation resulting in severe effects in duplex stainless steel components. However, crack propagation on a large scale in duplex alloys is likely to be limited by microstructural effects (sponsors: EPSRC, Geowaste/NDA Sellafield Ltd, NNL, RWM, Savannah River Nuclear Solutions).

The in-pond storage of AGR fuel in pH-moderated aqueous environment is also elucidated, linking the effect of pond chemistry (OH-/Cl-/T) to local corrosion susceptibilities of secondary phases, grain boundaries, and microstructure strain. The presence and location of NbC/NbCN play a crucial currently been carried out. (supported by EPSRC Distinctive, NDA, NNL).

The implementation of a deep-geological disposal concept bears a range of engineering and technological challenges, from understanding long-term material performance in aerobic-/unaerobic environments, to the production of full-scale high-purity waste canisters (for example, Cu with <5 ppm O, sub-ppm H).  A Knowledge Transfer Partnership (KTP) with BEP Surface Technologies has been successfully established, to understand the effect of electroplating parameters on production of electroformed KBS-3 type copper canisters. The type and concentration of organic additives was identified as key parameter for successfully maturing this technology, and the first miniature prototypes are currently in production. Links and collaborations with other government institutions, such as the Nuclear Waste Management Organization (NWMO, Canada) and KONICOF (Korea), have also been established. This project currently features as a potential REF Impact case study (REF2021), demonstrating the impact of academic support on UK plc. BEP, in collaboration with the academics from MPC’s waste group, currently hold discussions about expanding production capability abroad. Coating technology in storage and disposal scenarios is expected to feature in most EU geo-disposal programmes and landscapes. 

Novel routes to optimise cement/mortar microstructure for waste encapsulation and immobilisation are explored. Research is being conducted on the modelling of damage and fracture of cement-based materials, as well as on reactive transport of contaminants through porous and fractured media. The aim is, in combination with experimental data, to understand better the long-term behaviour of engineered barriers and near field and to support higher-fidelity predictions for the fate of radioactive waste in a deep geological repository. (supported by EPSRC/CGN).

The contamination of stainless steel surfaces and cementitious/concrete materials is investigated, with the aim to inform about the efficiency/applicability of different decontamination techniques. For example, laser scabbling of concrete microstructures was explored as a remote surface decontamination method, centred on the effect of concrete composition, ageing, and hydration on the decontamination efficiency. Current research focuses on providing a mechanistic understanding of fission product contamination (90Sr, 137Cs) of stainless steel microstructures in simulated storage pond and re-processing streams. Decontamination techniques, such as water jetting and electrochemical dissolution/removal are investigated. Laser Induced Breakdown Spectroscopy (LIBS), Glow Discharge-OES, and Secondary Ion-Mass Spectroscopy (SIMS), and high-speed cameras are applied to obtain information about ad-/absorption kinetics and characteristics of contaminants with real component (supported by Sellafield Effluent Centre/EPSRC/TWI).