Encapsulation of reactive metals in magnesium phosphate cement-based matrices

Magnesium phosphate cements (MPC) have been proposed to encapsulate aluminum and beryllium nuclear waste in a C-steel drum. Work has been dedicated to the MPC formulation by considering both the mechanical properties and the economical aspect. Indeed, the MPC cost is too high to envisage this type of cement for conditioning the radioactive waste at an industrial scale. First results have shown the impact of the MgO source and the nature of the filler. The behavior of MPC under leaching and irradiation has also been considered to determine their behavior in the storage conditions. During this period, attention has been paid on the methodology and the device for the leaching and irradiation experiments. Aluminum, beryllium and C-steel corrosion are studied in MPC (with a formulation already studied by the CEA) and in solutions mimicking the interstitial solutions of the cements. The results are compared to the ones obtained in commonly used cements in the storage, the ordinary Portland cement or the El-Cabril cement. The set-ups for the electrochemical and chromatographic measurements have been developed. Preliminary results have shown that Al and Al-Mg alloy are only in the passivity zone for the solution containing phosphate ions or for a mortar composed of MPC. This work has also put in evidence the inhibition effect of the boric acid, used as a retarder for the MPC, against the steel corrosion in neutral media (solutions or MPC).