用于中子吸收的铪酸铕陶瓷性能研究

Study on Performance of Europium Hafnate Ceramic for Neutron Absorbing

近年来,一些具有高熔点、无α粒子辐射优点的新型中子吸收材料被法国和日本等国提出。本研究以摩尔比为1:1的氧化铕和氧化铪混合物为原料,通过陶瓷烧结工艺研制了一种具有萤石稳定相的铪酸铕(Eu_(2)HfO_(5))中子吸收材料。对样品开展了包括熔点、热物性、力学性能等在内的一系列堆外测试。另外还进行了中子剂量达到1×10^(20)cm^(-2)的辐照考验,通过对比辐照前后的抗压强度等性能变化研究该材料的辐照性能。结果表明,所烧结的Eu_(2)HfO_(5)陶瓷中子吸收材料致密度高,物相为单一的萤石结构,熔点超过2 400℃,与理论值符合较好。同时该材料具有较好的亚临界水腐蚀性能。经过中子辐照后材料的密度和外观未发生明显改变,但中子吸收能力略有减小,抗弯强度和抗压强度略有增大。本研究得到了较为全面的堆外性能测试数据,并开展了辐照实验的考验,验证了所研制的Eu_(2)HfO_(5)陶瓷材料具备了预期的优点,为该材料的后续应用积累了基础数据。

Several new types of neutron absorbers with high melting points and non-alpha emit characteristics have been proposed by France and Japan in recent years.After comparison of the fuel assembly reactivity inserted with different rare earth oxide,the absorption effect of Eu2O3 mix with HfO2 is proven to be the best.The Eu_(2)HfO_(5)ceramic derived from the mixture of Eu2O3 and HfO2 with Mole ratio 1∶1 was fabricated shown fluorite phase.The preparation process was studied and multiple experiments on the physical characteristics of this ceramic material were performed.The measurement on density was examined by Archimedes’method.The measurement of linear thermal expansion coefficient was carried out by push-rod technique.The specific heat capacity at constant pressure test was conducted by high temperature differential scanning calorimetry.The thermal diffusivity was measured with laser flash diffusivity analyzer.The thermal conductivity was then calculated from equation with density,specific heat capacity at constant pressure and thermal diffusivity,the results is 1.66 W/(m·℃)under room temperature.The Young’s modulus was done with Grindo Sonic MK7.The melting point was tested in a non-container laser suspension furnace.The flexural strength,compressive strength was examined on universal testing machine.The micro-structure was observed on scanning electron microscope(SEM)KYKY EM6900.The subcritical water oxidation test was done in autoclave at 360℃.The density measurement and the XRD spectrum show the compactness and phase purity for the Eu_(2)HfO_(5)ceramic sample.SEM image demonstrates the grain size is around 5-15μm.The melting point of 2414℃measured by the dual-spectroscope is consistent with the theoretical value 2434℃.A weight gain of 0.6%is found after the subcritical water oxidation.The preparation process was also optimized and the density of the Eu_(2)HfO_(5)sample was improved.The thermophysical properties such as specific heat capacity at constant pressure,thermal diffusivity,thermal conductivity and compressive strength was tested for the new sample.This new type neutron absorber Eu_(2)HfO_(5)was irradiated with neutron flux up to1×10^(20)cm^(-2) on CMRR.For comparison,test before and after the irradiation was performed on the same machine.The post examination of the irradiation shows that there is no significant change with respect to appearance and density.However flexural strength and compressive strength increases a bit.The analysis of neutron radiograph for Eu_(2)HfO_(5)shows a decrease of neutron absorption ratio of 18.3%after irradiation while the computational simulation of neutron radiograph result gives an absorption ratio decrease of 2.3%.The comprehensive performance test data is obtained in this study,and irradiation experiment was performed which verifying the expected advantages for the fabricated Eu_(2)HfO_(5)ceramic.The accumulated basic data is valuable for the subsequent application of the material.