材料期刊网

自1942年首次在CP-1反应堆中使用以来,核石墨因其优异的综合性能,在核反应堆特别高温气冷堆中被广泛使用.作为第四代候选堆型之一,高温气冷堆主要包括球床堆和柱状堆两种堆型.在两种堆型中,石墨主要用作慢化剂、燃料元件基体材料及堆内结构材料.在反应堆运行中,中子辐照使得石墨的相关性能下降甚至可能失效.原材料及成型方式对于石墨的结构、性能及其在辐照中的表现起到决定性的作用.辐照中石墨微观结构及尺寸的变化是其宏观热力学性能变化的内在原因,辐照温度及剂量对于石墨的结构及性能变化起决定性作用.本文介绍了高温气冷堆中核石墨的性能要求及核石墨的生产流程,阐述了不同温度及辐照条件下石墨热力学性能及微观结构的变化规律,并对当前国内外核石墨的研究现状及未来核石墨的长期发展如焦炭的稳定供应和石墨的回收进行讨论.本文可为有志于研发用于未来我国商业化的高温气冷堆中的核石墨的生产厂家提供参考.

Since its first successful use in the CP-1 nuclear reactor in 1942, nuclear graphite has played an important role in nuclear reactors especially the high temperature gas-cooled type (HTGRs) owing to its outstanding comprehensive nuclear properties.As the most promising candidate for generation IV reactors, HTGRs have two main designs, the pebble bed reactor and the prismatic reactor.In both designs, the graphite acts as the moderator, fuel matrix, and a major core structural component.However, the mechanical and thermal properties of graphite are generally reduced by the high fluences of neutron irradiation of during reactor operation, making graphite more susceptible to failure after a significant neutron dose.Since the starting raw materials such as the cokes and the subsequent forming method play a critical role in determining the structure and corresponding properties and performance of graphite under irradiation, the judicious selection of high-purity raw materials, forming method, graphitization temperature and any halogen purification are required to obtain the desired properties such as the purity and isotropy.The microstructural and corresponding dimensional changes under irradiation are the underlying mechanism for the changes of most thermal and mechanical properties of graphite, and irradiation temperature and neutron fluence play key roles in determining the microstructural and property changes of the graphite.In this paper, the basic requirements of nuclear graphite as a moderator for HTGRs and its manufacturing process are presented.In addition, changes in the mechanical and thermal properties of graphite at different temperatures and under different neutron fluences are elaborated.Furthermore, the current status of nuclear graphite development in China and abroad is discussed, and long-term problems regarding nuclear graphite such as the sustainable and stable supply of cokes as well as the recycling of used material are discussed.This paper is intended to act as a reference for graphite providers who are interested in developing nuclear graphite for potential applications in future commercial Chinese HTGRs.