Magnesium Potassium Phosphate Cement for Low- And Intermediate-Level Radioactive Waste Conditioning: Advances, Limitations and Future Trends

Low- and intermediate-level radioactive waste (LILRW) comprises a highly heterogeneous range of materials that require immobilisation matrices capable of ensuring mechanical stability, chemical compatibility, and limited radionuclide mobility over extended time scales. Conventional cementitious binders, such as Portland cement (PC) and alkali-activated systems, are widely used for waste conditioning but may present limitations when applied to waste streams incompatible with highly alkaline environments, including certain reactive metals and ion-exchange resins. Magnesium potassium phosphate cement (MKPC) has emerged as a promising alternative binder due to its near-neutral pore solution pH, low water demand, rapid setting behaviour, and the formation of stable crystalline phases such as K-struvite. This review synthesises current knowledge on MKPC as a conditioning matrix for LILRW, with particular attention to the formulation parameters that control its reaction kinetics, phase assemblage, and the microstructural development. Key aspects examined include MgO reactivity, MgO/KH 2 PO 4 molar ratio, water content, chemical retarders, mineral additions, and curing conditions. The implications of these parameters for key material properties relevant to waste immobilisation, such as mechanical strengths, pore solution chemistry, porosity, durability under leaching, corrosion and irradiation, are critically assessed. Overall, the available evidence highlights the potential of MKPC as a promising binder for challenging LILRW streams, while also identifying key knowledge gaps related to long-term performance under repository-relevant conditions, radionuclide retention mechanisms, broader radionuclide coverage, and formulation optimisation before large-scale implementation can be fully realised.