UN-U3Si2复合芯块放电等离子体烧结制备工艺与性能表征研究

Research on Preparation Process by Spark Plasma Sintering and Performance Characterization of UN-U3Si2 Composite Pellet

  • 摘要: 为进一步提升核燃料的安全性和可靠性,本文以UN-U3Si2复合芯块为研究对象,采用放电等离子体烧结技术,结合微观形貌观察、化学成分测试、热物理和力学性能测量等表征方法开展系统研究。通过正交试验研究了烧结温度、保温时间、烧结压力对复合芯块致密度的影响,通过UN和U3Si2粉末不同粒径之间的组合,研究粉末粒径对复合芯块致密度的影响,通过调整混合比例,研究不同U3Si2含量对复合芯块的热导率、硬度和抗压强度等性能的影响。结果表明,UN-20%U3Si2复合芯块最佳烧结参数为:烧结温度为1 650 ℃、保温时间为30 min、烧结压力为50 MPa,制备得到的复合芯块密度为13.60 g/cm3,相对密度为98.30%,3种因素对复合芯块密度影响的显著程度为烧结温度>烧结压力>保温时间。细UN-粗U3Si2制备的UN-20%U3Si2复合芯块的密度最大,为13.60 g/cm3,相对密度为98.31%。UN-20%U3Si2的复合芯块综合性能最优,热导率达到29.0 W/(m·K)@900 ℃,热膨胀系数达到8.90×10−6 K−1@600 ℃,硬度为637 HV1,抗压强度为331.0 MPa。本文的试验结果能够为后续UN-U3Si2复合芯块的研究和应用提供一定的基础。

     

    Abstract: After the Fukushima nuclear accident in 2011, the international community has put forward higher requirements for the safety and reliability of new generation nuclear power plants and nuclear fuels. As an important measure to improve the safety performance, the development of accident tolerant fuel (ATF), which can tolerate accidents to a certain extent and has inherent safety, has become an important direction for the development of the nuclear fuel field. Due to the relatively low melting point of U3Si2, it can be used as a second phase to be mixed with UN for sintering, and the sintering temperature of pure UN can be reduced by taking advantage of the characteristics of liquid-phase sintering. U3Si2 phase can also stabilize the grain boundary interface of UN, and cause UN cracking mainly transgranular fracture. It can limit the exposure of the fresh surface and improve the water vapor corrosion resistance of the pellet to a certain extent. Therefore, UN-U3Si2 composite pellet has become a current research hotspot. In this paper, UN-U3Si2 composite pellet was studied systematically by spark plasma sintering combined with characterization methods, including microstructural observation, chemical composition test, thermomechanical and mechanical properties measurement. The effects of sintering temperature, holding time and sintering pressure on the densification of composite pellets were studied by orthogonal experiments. The influence of particle size on the densification of composite pellets was studied through the combination of different UN and U3Si2 powders. The effects of different U3Si2 content on thermal conductivity, hardness and compressive strength of composite pellets were studied by adjusting the mixing ratios, and the reason for the variation of thermal conductivity of the composite pellet with the mixing ratio was analyzed. The results indicate that the optimal sintering parameters for UN-20%U3Si2 composite pellet are sintering temperature of 1 650 °C, holding time of 30 min, and sintering pressure of 50 MPa. Under these conditions, the pellet density reaches 13.60 g/cm3, and the relative density is 98.30%. The significance of the influence on pellet density is sintering temperature>sintering pressure>holding time. The density of UN-20%U3Si2 composite pellet prepared by fine UN and coarse U3Si2 powders is the highest, which is 13.60 g/cm3, and the relative density is 98.31%. The UN-20%U3Si2 composite pellet has the best comprehensive performance, with thermal conductivity of 29.0 W/(m·K) at 900 ℃, thermal expansion coefficient of 8.90×10−6 K−1 at 600 ℃, hardness of 637 HV1, and compressive strength of 331.0 MPa. The experimental results of this paper can provide a certain basis for the subsequent research and application of UN-U3Si2 composite pellet.

     

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