Immobilization of reactive metal wastes in low pH magnesium potassium phosphate cement matrices

Reactive metal wastes produced across various nuclear fuel cycle operations, such as fuel cladding, coolants, structural components, and incineration residues, present severe conditioning challenges for long-term disposal. Encapsulating these reactive metals in conventional Portland cements triggers rapid metallic corrosion due to the highly alkaline pore environment (). This corrosion drives hydrogen gas evolution and expansive mineral formation, compromising the structural integrity of the waste form and risking repository safety.

Magnesium potassium phosphate cements (MKPCs) offer a viable alternative due to their near-neutral pore solution (), rapid strength development, low water demand, and inherent chemical passivation capabilities through insoluble phosphate formation. This research investigates the immobilization and interfacial stability of simulated reactive metal wastes ( or ) within an optimized MKPC binder. The study focuses on formulating high-loading waste forms that comply with nuclear waste acceptance criteria regarding fresh-state workability, setting kinetics, and early/late-age mechanical strengths. Metal-matrix compatibility will be systematically evaluated by monitoring volumetric expansion and gas evolution, alongside high-resolution microstructural and phase analysis (SEM-EDS, XRD) to understand the reaction mechanisms at the metal-binder interfacial transition zone.