| High-level radioactive waste(HLW)was the product of spent fuel produced by the use of nuclear energy in military and commercial fields,which has great radiation hazards.Glass–ceramics composite matrix,as an immobilization matrix for the HLW,had prospects for development.In the present work,the ceramic powder was prepared by the solid phase method.The optimal calcination temperature was found to be 1300 oC,which was the lowest calcining temperature to prepare powder without impurity.Ceramic-doped ceramic powders were prepared using an optimized calcining process.The particle size of the powders decreased gradually with the increase of doping content,the particle size of Nd doped powder decreased from 2um to 1.4um;the particle size of Hf doped powder decreased from 1.5um to 0.8um;and the particle size of Nd-Hf doped powder decreased from 1.2um to 0.6um.With the increase of sintering temperature,the density of glass-ceramics matrix prepared by solid-state method first increased and then decreased,and the maximum density of 3.577 g·cm-3 was obtained when the sintering temperature was 710 oC.When the sintering temperature was fixed at 710 oC,the density of glass-ceramics matrix decreased first and then increased with the prolongation of sintering time.The density reached the maximum value of 3.58g·cm-3 when the sintering time was 3h.Accordingly,it was determined that the optimized sintering condition for glass-ceramics matrix was at the temperature of 710 oC for 3h.No impurity phase was found for the Nd-doped,Hf-doped and Nd-Hf co-doped glass-ceramics matrix sintered at 710 oC for 3h.As the doping amount increased the density of the three glass-ceramics matrix decreased first and then increased.The undoped glass-ceramics matrix showed the highest density and the glass-ceramics with an element doping ratio of 0.4 exhibited the lowest density.The lowest bulk density of the Nd,Hf and Nd-Hf doped glass-ceramics matrix were 2.78 g·cm-3,2.83 g·cm-3 and 2.78 g·cm-3,respectively.The hardness of all the glass-ceramics matrix showed a trend of first decreasing then increasing with the increase of doping amount,and reached the maximum value when the element doping ratio was 0.2.The maximum hardness of Nd,Hf and Nd-Hf doped glass-ceramics matrix were 5.88 GPa,6.26 GPa and 4.71 GPa,respectively.The Nd,Hf and Nd-Hf doped glass-ceramics systems all reached the minimum hardness when the doping ratio was 0.4,being 1.82 GPa,1.44 GPa and 0.93 GPa,respectively.The compressive strength of the three doping systems first decreased then increased with the increase of doping amount.The undoped glass-ceramics showed the highest compressive strength of 552.6MPa and the three doping systems all reached the minimum compressive strength with the doping ratio of 0.4.The minimum compressive strength of the Nd,Hf and Nd-Hf doped glass-ceramics matrix were 187.2MPa,186.30 MPa and 126.8MPa,respectively.The coefficient of linear expansion of the glass-ceramics matrix of the three doped systems showed a linear increase with increasing temperature.The coefficient of thermal expansion of the glass-ceramics matrix of all components was approximately the same at 500 oC,being around 11×10–6·K–1.No change in phase and surface morphology was observed in the leaching test of glass-ceramics at normal temperature and pressure.After 7 days' leaching in the aqueous solution under high temperature and high pressure,the glass network on the surface of the glass-ceramics matrix dissolved,with barium titanate of pyrochlore phase as well as an amorphous material formed on the surface.After 7 days' corrosion under the condition of high temperature and high pressure in water vapor,the glass network on the surface of the glass-ceramics matrix dissolved as well,and an amorphous phase was generated on the surface,which was different from that in the aqueous solution. |
PDF Full Text Request