Rapid solidification of Highly Loaded High-Level Liquid Wastes with magnesium phosphate cement

Rapid solidification of radioactive wastes is one of the most effective methods to prevent the spreading of radioactive contamination after a nuclear emergency. In this study, magnesium phosphate cement (MPC) was used as matrix to rapidly solidify denitrated high-level liquid wastes (HLLW). The compressive strengths and leaching rates of the samples were studied to evaluate the performance of the solidification forms. Further, XRD, SEM, and EDS were used to measure phase compositions, microstructures, and microscopic chemical compositions, respectively, of the as-prepared samples. Moreover, the solidification mechanism of simulated radioactive ions in phosphate cement is discussed in this paper. According to the results, the compressive strength of the solidified forms was affected by the actual mass ratio of dead-burned magnesia (MgO) powders to potassium dihydrogen phosphate (KH2PO4) (M/P) and unreacted KH2PO4; with up to 50 wt% HLLW content, 4.2 MPa and 13.2 MPa can be achieved for an M/P ratio of 1 after 3 h and one day, respectively. The leaching rates of Sr2+ and Cs+ for the solidified forms were below 10(-7) g/m(2)/d and 10(-4) g/m(2)/d, respectively. The immobilization of radioactive ions via an MPC paste is not only due to chemical immobilization, but also due to the physical encapsulation offered by the dense structure of the MPC. The cement offers sufficient strength in a short time for the temporary storage and transportation of the solidified forms.