Study On Durability Of Emergency Curing Material Of Magnesium Phosphate Cement

As one of the important new energy sources in human society,nuclear energy is a kind of national strategic energy with high energy density.The efficient and safe use of nuclear energy is the focus at present,especially the related safety technology directly affecting the smooth development of nuclear energy.However,many problems,such as nuclear accidents,the disposal of radioactive waste and the spread of nuclear pollution,hinder the development and utilization of nuclear energy.Among them,to maximize nuclear energy’s social,economic,and environmental benefits,the disposal of radioactive nuclear waste is particularly critical.The high-level liquid waste in radioactive nuclear waste has always been the key point and difficulty.Reasonable,efficient and rapid treatment,reducing nuclear leakage and nuclear pollution is the top priority of waste disposal.Based on this starting point,this paper intends to use magnesium phosphate cement to solidify the simulated high-level radioactive waste liquid quickly,and on this basis,the cement solidified body is sintered and ceramic,through the analysis of the long-term stability of the solidified body,to evaluate the efficiency of magnesium phosphate cement（MPC）in the treatment of high-level radioactive waste and the feasibility of proper storage of the solidified body.In this paper,the long-term stability of MPC was tested,the mechanical properties and durability of magnesium oxide to phosphate with a different mass ratio of magnesium oxide to phosphate（M/P ratio）were studied,and its microstructure and microstructure were analyzed systematically.The conclusions are as follows:the compressive strength of MPC of curing 3h cement solidified body with different M/P ratio（mass ratio 1-5）can meet the requirements of GB14569.1-2011 for cement solidified body.Increasing the M/P ratio will decrease the solidified body’s hydration peak temperature and hydration rate.The solidification of MPC for Cs⁺includes the effect of physical encapsulation on the crystallization products of Cs⁺and the combination of Cs⁺chemical reaction to form insoluble substances,and the curing effect of Sr²⁺is also excellent,and the leaching rate and cumulative leaching fraction of both are much lower than those required in the national standard.;the MPC solidified body has good water resistance,and the minimum strength loss of 90 days is 5.68%.The strength loss of 5 freeze-thaw cycles meets the national standard requirements,and the solidified body has good long-term stability.Secondly,the ceramics of MPC solidified body was studied under different sintering temperatures（700℃,900℃,1100℃,1400℃）and different holding times（30min,60min,120min）.The results show that after sintering,the solidified body will form a ceramic-like structure,the overall density increases,the structure is more complete,and the performance indexes are improved obviously.By using the Product Consistency Test-A（PCT-A）method,the minimum leaching concentration and cumulative leaching fraction of soaking Cs⁺,Sr²⁺at90℃for 7 days were 0.0765,1.375mg/L and 1.95E-05,2.95E-05 g/（m~2·d）,respectively,and the strength loss of immersion resistance and freeze-thaw cycle resistance was less than 25%.Furthermore,the MPC solidified body has good acid resistance.After sintering,magnesium silicate（Mg Si O₃,Mg₂Si O₄）,trimagnesium phosphate（Mg₃（PO₄）₂）and magnesium ferric phosphate products replacing K position are produced.With the increase of sintering temperature,many molten phases are produced in the solidified body,the transformation and reaction between the phases are rapid,the overall structure is more compact,and the properties of the ceramic solidified body are good.Finally,the proportion of cement solidified body was optimized by changing the content of glass powder and iron powder,and 1100℃and heat preservation 30min were selected to study the ceramics of cement solidified body.The results show that when the glass powder content reaches 40%,the solidified body has a denser structure,which adds 40%glass powder.The standardized leaching rates of Cs⁺in the two groups with iron powder content of 5%and 10%were 2.30,2.58(10^-5)（g/（m~2·d））,respectively,which were about 53.6%and48%lower than those of Cs⁺at the same sintering temperature（1100℃）.Similarly,the reduction of Sr²⁺is about 96.3%and 90%.Soaking performance,five freeze-thaw cycles and acid and alkali resistance have improved further.To sum up,on the one hand,MPC can realize the rapid solidification of high-level liquid waste,and the cement solidified body has good long-term stability and can meet the requirements of temporary storage and transportation;on the other hand,high-temperature sintering ceramic can be used as an important means to improve the performance of solidified body,and it can meet the requirements of long-term storage by forming dense ceramic structure.