Abstract
For the proposed novel procedure of immobilizing HLW with magnesium potassium phosphate cement (MKPC), Fe2O3 was added as a modifying agent to verify its effect on the solidification form and the immobilization of the radioactive nuclide. The results show that Fe2O3 is inert during the hydration reaction. It slows down the hydration reaction and lowers the heat release rate of the MKPC system, leading to a 3°C-5°C drop in the mixture temperature during hydration. Early comprehensive strength of Fe2O3 containing samples decreased slightly while the long-term strength remained unchanged. For the sintering process, Fe2O3 played a positive role, lowering the melting point and aiding the formation of ceramic structure. CsFe(PO4)2, or CsFePO4, was generated by sintering at 900°C. These products together with the ceramic structure and absorption benefit the immobilization of Cs+. The optimal sintering temperature for heat treatment is 900°C; it makes the solidification form a fired ceramic-like structure.
Highlights
The utilization of nuclear energy resulted in the accumulation of large amounts of liquid high-level radioactive waste (HLW) which contains environmentally hazardous elements like plutonium and other actinides in addition to fission and corrosion products [1]
Fe2O3 was added at a dosage series of 0%, 3%, 6%, 9%, and 12% to investigate the effect on MKPC hydration
magnesium oxide (MgO)’s dissolution in an acid solution as well as the hydration reaction release heat to make up the two exothermic peaks
Summary
The utilization of nuclear energy resulted in the accumulation of large amounts of liquid high-level radioactive waste (HLW) which contains environmentally hazardous elements like plutonium and other actinides in addition to fission and corrosion products [1]. The dominant technology for the solidification of HLW is vitrification. The technology of immobilizing HLW through vitrification does not ensure the complete immobilization of radionuclides due to the low hydrothermal stability of the glass produced [2]. The incorporation of radionuclides into crystalline phases (pyrochlore, zircon, zirconolite, etc.) that are analogs to natural minerals and that have high radiation and chemical stability is considered as an alternative way for vitrification. As alternative materials for vitrification, various matrices were proposed for immobilization of HLW including hydrothermal synthetic rock [4,5,6], ceramics [2], and Portland cement [7]
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