Hydrolytic and thermal stability of magnesium potassium phosphate compound for immobilization of high level waste

The samples of the magnesium potassium phosphate (MPP) compound have been synthesized during solidification of high level waste (HLW) surrogate. The compound consists of a main phosphate phases Mg(1.1)Na(0.35)K(0.45)PO(4)x(4-6)H2O and MgCs(0.5)Na(0.2)K(0.3)PO(4)x(5-6)H2O. Differential leaching rates of Pu-239, Eu-152 and Sr-90 from the MPP compound after heat treatment (450 degrees C) are 7.8x10(-9); 1.7x10(-7) and 8.8x10(-6)gcm(-2) day(-1), respectively. The coefficient of thermal expansion of MPP compound(11.6 +/- 0.3)x10(-6)degrees C-1; coefficient of thermal conductivity averages 0.5Wm(-1)K(-1). The properties of MPP compound meet the regulatory requirements for solidified HLW.