Chemical Compatibility between Eu₂O₃-ZrO₂ Ceramics and 316L Stainless Steel AITranslate

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Basic Information:

DOI：10.13373/j.cnki.cjrm.XY25010018

Chinese Library Classification Number:TG142

Citation Information:

With the rapid development of the nuclear industry，the safety of nuclear reactors has become a global concern. During normal operation or accident scenarios，control rods may undergo chemical interactions with their cladding materials upon contact，thereby affecting their service life. As new control rod materials are developed，investigating the chemical compatibility between control rods and their cladding materials is crucial. Eu₂O₃，with its high thermal neutron absorption cross-section and high melting point，is a suitable neutron-absorbing material for control rods in nuclear reactors，particularly under high-temperature operating conditions. However，Eu₂O₃ exhibits relatively poor chemical stability in water or humid air. Given its high thermal neutron absorption cross-section and melting point，and the fact that the addition of ZrO₂ can enhance its chemical stability，Eu₂O₃-ZrO₂ ceramics are considered a promising candidate material for new accident-tolerant control rods. Meanwhile，316L stainless steel，known for its excellent corrosion resistance and mechanical properties，is widely used for structural components in nuclear reactors. Therefore，the chemical compatibility of Eu₂O₃-ZrO₂ ceramics with 316L stainless steel cladding under accident conditions has attracted significant attention. To study the chemical compatibility between Eu₂O₃-ZrO₂ ceramics and 316L stainless steel，this paper investigated the compatibility by forming a diffusion couple through close contact between Eu₂O₃-ZrO₂ ceramics and 316L stainless steel. The study focused on the chemical compatibility under simulated accident temperatures （1000~1200 ℃） after heat treatment for 20~60 h. Eu₂O₃-ZrO₂ ceramics with a molar ratio of Eu₂O₃∶ZrO₂=2∶1 was used in the experiment. The microstructure of the diffusion couple interface was analyzed using scanning electron microscopy （SEM） and energy-dispersive spectroscopy （EDS） to reveal the chemical compatibility and interdiffusion behavior between Eu₂O₃-ZrO₂ ceramics and 316L stainless steel cladding under simulated accident conditions. The experimental results showed that the surface of Eu₂O₃-ZrO₂ ceramics changed from brown to yellow. Measurements of the sample dimensions revealed no significant changes before and after the experiment，indicating the preservation of the ceramics' apparent mass and structural integrity. Macroscopic observations of 316L stainless steel revealed the formation of a thin film on its surface. X-ray diffraction （XRD） analysis of the film on the surface of 316L stainless steel showed the presence of a small amount of SiO₂ phase，with no other phases detected. EDS results indicated that the main components of the film were Eu，O，Cr，and Si，with Eu content ranging from 24.37% to 33.49%，Cr content from 9.15% to 11.57%，O content from 43.24% to 54.70%，and Si content from 0.75% to 7.68%. Interface reactions occurred between Eu₂O₃-ZrO₂ ceramics and 316L stainless steel at the interface，accompanied by mutual diffusion of elements. Fe，Cr，Ni，and Si from 316L stainless steel，as well as Eu and O from the ceramics，diffused toward the interface. Eu and O diffused into the stainless-steel matrix，while Si accumulated in the diffusion zone within 316L stainless steel matrix. For the cross-section of 316L stainless steel，after heat treatment at 1000 ℃ for 20~60 h，the diffusion distances of the elements were 7.51，10.71，and 15.45 μm，respectively. After heat treatment at 1100 ℃ for 20~60 h，the diffusion distances were 13.53，18.15，and 22.80 μm，respectively. After heat treatment at 1200 ℃ for 20~60 h，the diffusion distances were 20.19，32.89，and 36.40 μm，respectively. In the chemical compatibility experiment at 1200 ℃ for 60 h，interface reactions between Eu₂O₃-ZrO₂ ceramicsand 316L stainless steel occurred，resulting in a decrease in Fe content in stainless steel from an initial 70.52% （non-diffusion zone） to 7.75% （diffusion zone），a decrease in Cr content from 16.73% to 2.58%，a decrease in Ni content from 9.44% to 0.95%，and an increase in Si content from 0.75% to 14.35%. Meanwhile，Eu and O contents in 316L stainless steel increased from the initial 0 to 30.28% and 44.09%，respectively，indicating the diffusion of Eu and O from the ceramics into the stainless steel matrix. The diffusion depth as a function of temperature and time was plotted as Δx² against time t，and linear fitting was performed to obtain the diffusion coefficients of Eu at different temperatures. Under heat treatment conditions of 1000~1200 ℃ for 20~60 h，the diffusion coefficients of Eu in stainless steel were （9.93±1.05）×10^-16，（2.38±0.05）×10^-15，and （6.49±0.46）×10^-15 m²·s^-1，respectively. The data indicated that the diffusion coefficient of Eu increased with temperature. Therefore，the reaction rate of Eu₂O₃-ZrO₂ ceramics with 316L stainless steel could be predicted within the temperature range of 1000~1200 ℃ using diffusion kinetics. This helpedto estimate its service life and mitigate the impact and damage of accidents. The diffusion reaction kinetics at the interface were further analyzed，and Arrhenius relationship between the diffusion coefficient （k） of Eu in 316L stainless steel and temperature （T） was established as：lnk=–（20.80±1.06）–（1.46±0.12）×10⁵/RT，where R is the gas constant and T is the temperature in Kelvin. The diffusion activation energy of Eu was calculated to be （146±12） kJ·mol^-1 using Arrhenius equation. Temperature was the primary factor affecting the chemical compatibility between Eu₂O₃-ZrO₂ ceramics and 316L stainless steel. Studying their chemical compatibility under accident conditions helped to ensure that no harmful chemical reactions occur between the control rod materials and the reactor structural materials under high-temperature conditions，thereby enhancing the safety and reliability of nuclear reactors.