核燃料包壳锆合金表面铬涂层研究进展

锆合金凭借其较低的热中子吸收截面、优异的抗辐照性能以及良好的核燃料相容性等优点,被广泛应用于压水堆燃料包壳.福岛核事故后,表面铬涂层改性的锆合金成为耐事故包壳材料的重点研究方向之一,被认为是短期内最有可能投入商业应用的技术.综述了近年来核燃料包壳锆合金表面铬涂层的研究成果.介绍了铬涂层在事故条件下和正常工况条件下的性能优势,分析了其与锆合金基体在热性能上的匹配特性,重点对比了现有的铬涂层制备方法的优缺点,包括激光熔覆、喷涂、物理气相沉积等.其中激光熔覆和喷涂技术具有沉积速度较快、工艺条件相对简单的特点,但涂层厚度和粗糙度偏高,均匀性较差.物理气相沉积技术制得的涂层综合性能好,不足之处是涂层沉积速率较低,沉积过程需要高真空环境.兼顾高质量和低成本且适合商业化生产的包壳管表面铬涂层制备工艺仍有待于深入研究.归纳了铬涂层的高温氧化失效机制,提出在高温氧化过程中,涂层的分层、残余铬层的消耗以及锆元素沿铬晶界的扩散,是产生氧快速扩散通道并最终导致涂层失效的主要原因.最后指出了当前研究中存在的若干问题及其解决措施,为包壳锆合金表面铬涂层的进一步研究提供参考.

Research Progress of Chromium Coating on Zirconium Alloy for Nuclear Fuel Cladding

Zirconium alloy is widely used in pressurized water reactors fuel cladding due to its lower thermal neutron absorption cross section, excellent radiation resistance, good nuclear fuel compatibility, etc. After the Fukushima nuclear accident, zirconium alloy modified by the surface chromium coating has become one of the key research directions of accident tolerant fuel cladding materials, and is considered to be the technology which is most likely to be put into commercial application in the short term. The paper reviewed recent research results of chromium coating on zirconium alloy for nuclear fuel cladding. The performance advantages of the chromium coating under the accident and normal working conditions were introduced; and the matching characteristics of chromium coating with zirconium alloy substrate in thermal properties were analyzed. The advantages and disadvantages of the existing chromium coating preparation methods, including laser cladding, spray coating, physical vapor deposition were compared emphatically. Among them, laser cladding and spraying technology had the characteristics of faster deposition speed and relatively simpler process condition, but their coating thickness and roughness were high, and their uniformity was poor. However, the coating prepared by physical vapor deposition technology had good overall performance, but the disadvantages were lower coating deposition speed and high vacuum environment required in the deposition process. It still required studying further for the preparation processes of the surface chromium coating on cladding tube suitable for commercial production and considering both high quality and low cost. The high-temperature oxidation failure mechanism of chromium coatings was summarized. It was proposed that the delamination of the coating, the consumption of the residual chromium layer and the diffusion of zirconium element along the chromium grain boundary during the high temperature oxidation process were the main reasons for the formation of rapid oxygen diffusion channels, which resulted in the coating failure ultimately. Finally, several problems and their solutions in the current research were put forward, which provided a reference for further research on the surface chromium coating of the cladding zirconium alloy.