Low-temperature immobilization of actinides and other components of high-level waste in magnesium potassium phosphate matrices

The magnesium potassium phosphate (MPP) matrices formed by the room-temperature reaction of MgO and KH2PO4 solution were used for immobilization of simulated liquid alkaline high-level waste (HLW) containing actinides, fission and corrosion products. Novel procedures of solidification of HLW simulants were developed to increase stability of the MPP matrices to leaching radionuclides (Pu, Np, Am, Cs, Sr, Tc, I and Se), matrix-forming (K, Mg and PO4) and admixture components (NO3, NO2, Na and others) as well as hazardous elements (Pb, Cr, Zn and others) according to the ANS, PCT, TCLP standards. Density (∼1.7 g/cm3), compressive strength (>20 MPa), radiation resistance of the matrices and chemical yield of radiolytic hydrogen (0.004 molecule H2/100 eV) were determined. The phase composition of the matrices and distribution of radionuclides were studied by XRD and autoradiography correspondingly.