Struvite-Based Matrices for Solidification of High-Salt Boron-Сontaining Liquid Radioactive Wastes

Processes occurring when struvite (potassium-magnesium and ammonium–magnesium phosphates) matrices are formed in high-salt boron-containing model solutions simulating the evaporated still bottoms from a nuclear power plant with PWR reactors were examined. Relations were obtained, describing how the strength of the matrices depends on the content of salts in a matrix, and the main phases responsible for the strength were determined. It was shown that the matrices synthesized at the stoichiometric ratio between the reagents, MgO and NH 4 H 2 PO 4 , fail to satisfy the requirements to cemented radioactive wastes as regards the strength and leaching of β-radionuclides. Introduction of a 10–20% excess of MgO during the synthesis of the matrices makes it possible to significantly improve the strength of the matrices and diminish the degree of 137 Cs leaching. Matrices were obtained containing up to 17–17.5 wt % salts, which is 1.7–2.5 times larger than that in portland cement matrices. These matrices fully satisfy the requirements to cemented radioactive wastes.