摘要
UO_(2)-Zr燃料体系广泛应用于压水反应堆和各种研究试验堆中,但在反应堆运行工况下,UO_(2)燃料与Zr包壳会发生扩散反应。在UO_(2)燃料与Zr包壳之间制备一层氧扩散阻挡层,阻止UO_(2)中的氧原子向Zr包壳中扩散,是提高核燃料元件的安全性和使用寿命的方法之一。进行理论计算,结果表明Nb和Cr是最具潜力的氧扩散阻挡层材料。采用电弧离子镀技术制备Nb、Cr、Nb/Cr三种涂层,通过对这三种扩散阻挡层的研究,发现在UO_(2)燃料上制备一层金属涂层能够有效阻止UO_(2)与Zr包壳的扩散反应,Nb涂层具有较好的氧阻挡能力,但是Nb与Zr在试验条件下能够无限固溶,形成Nb与Zr的双相结构。Cr与UO_(2)燃料和Zr包壳均有较好的相容性,但是Cr与O原子的亲和性比Nb好,Cr涂层中O原子浓度比Nb涂层中的O原子浓度高。Nb/Cr复合涂层是一种比较理想的扩散阻挡层,且靠近UO_(2)燃料一侧为Nb涂层,靠近Zr包壳一侧为Cr涂层。研究结果表明Nb/Cr复合涂层作为氧阻挡层材料,在氧阻挡能力上优于Nb涂层和Cr涂层。扩散反应阻挡层的研究可为提高核燃料元件的安全性和使用寿命提供一定参考数据。
UO_(2)ceramic nuclear fuel is characterized by high hardness,a high melting point,and radiation resistance.Consequently,UO_(2)fuel has been widely used in pressurized water reactors and various research and experimental reactors.UO_(2)ceramic nuclear fuel pellets are encapsulated in a Zr cladding material to produce fuel elements that are now the mainstream fuel elements for pressurized water reactors owing due to their high strength,plasticity,and thermal conductivity.However,under reactor operating conditions,the UO_(2)fuel and Zr shell are thermodynamically unstable,and the O atoms in UO_(2)can diffuse into Zr,forming ZrO_(2)and other brittle phases that affect the safety and service life of nuclear fuel assemblies.Following the Fukushima accident,higher standards for reactor safety and longevity are demanded worldwide.Fuel assembly safety studies have shown that the formation of an oxygen diffusion barrier layer between the UO_(2)fuel phase and Zr shell to prevent the diffusion of oxygen atoms from the UO_(2)phase into the Zr shell is a method for improving the safety and service life of nuclear fuel assemblies.The calculations indicated that Nb and Cr are potential materials for diffusive barrier layers.To investigate the ability of Nb and Cr as diffusive barrier materials for preventing the diffusion of oxygen atoms,Nb,Cr,and Nb/Cr coatings were fabricated on Zr plates via arc-ion plating.Subsequently,the Zr plates with different coatings were tightly bonded to the UO_(2)plates to form a sandwich diffuser.The diffusing couple was placed in a mold,filled and packed with Zr powder,and placed in a sintering furnace to prepare for the diffusion reaction.Vacuum thermal pressing was used to accelerate diffusion.The experimental conditions of diffusion reaction were as follows:pressure of 50 MPa,reaction temperature of 800°C,hold temperature time of 4 hours,and furnace cooling were employed.After hot-press sintering,the diffusing couple was cut in the middle to observe and analyze the cross section.Scanning electron microscopy and energy dispersive spectroscopy were used to observe the morphology and analyze the elements.The results showed that the metallic coating effectively prevented diffusion between UO_(2)and Zr.Comparative studies have found that Nb coatings have more optimized oxygen resistance;however,Nb and Zr diffuse and form a two-phase structure under experimental conditions.The mutual diffusion of Nb and Zr atoms results in a large number of Zr atoms in the Nb coating and a large number of Nb atoms in the Zr shell.Cr was compatible with UO_(2)and Zr,and no diffusion reactions were observed between UO_(2)and Zr under the experimental conditions.However,Cr atoms have a greater affinity for O atoms than for Nb atoms,and the concentration of O atoms in the Cr coatings is higher than that in the Nb coatings.If the Cr coating is thin,O atoms can pass through the Cr coating,enter the Zr shell,and affect its properties.In summary,at this limit,a metallic coating can effectively prevent the diffusive reaction between UO_(2)and Zr.However,a single Nb or Cr coating does not completely solve the problem of diffusion between UO_(2)and Zr.Based on these results,a Nb/Cr composite layer to solve the diffusion problem between the UO_(2)fuel and the Zr shell may be a better approach.The side near the UO_(2)fuel was coated with Nb and that near the Zr shell was coated with Cr.The study of the diffusive reaction barrier layer between the UO_(2)fuel and Zr shell provides reference for improving the safety and service time of nuclear fuel assemblies.
作者
黄杰
曾强
刘喆
陈江善
李浩鹏
廖斌
HUANG Jie;ZENG Qiang;LIU Zhe;CHEN Jiangshan;LI Haopeng;LIAO Bin(Nuclear Power Institute of China,Chengdu 610200,China;College of Nuclear Science and Technology,Beijing Normal University,Beijing 100875,China)
出处
《中国表面工程》
EI
CAS
CSCD
北大核心
2024年第2期220-226,共7页
China Surface Engineering
关键词
核燃料
扩散阻挡层
相容性
涂层
nuclear fuel
diffusion barrier layer
compatibility
coating
