Preparation Process And Performance Optimisation Of Microcrystalline Graphite-based Nuclear Grade Graphite

High-temperature gas-cooled reactor is a fourth-generation advanced nuclear energy system,which can be divided into spherical bed reactor and prismatic reactor according to the fuel elements.China has set spherical bed type high-temperature gascooled reactor as the development direction,and has built the high-temperature gascooled experimental reactor HTR-10 and high-temperature gas-cooled demonstration plant HTR-PM.During this period,more than 1200 tons of imported nuclear graphite IG-110 were used for reactor core structural components,moderator and reflector layer materials,whose performance directly affects the service life and economy of the hightemperature gas-cooled reactor.As the main structural material of high-temperature gas-cooled reactors,the localization of nuclear graphite is an important prerequisite for the commercialization of high-temperature gas-cooled reactors.The basic characteristics of raw materials determine the performance of nuclear graphite to a certain extent.At present,commercial nuclear graphite is mainly prepared from petroleum coke and asphalt coke,and its irradiation life cannot meet the design requirements of high-temperature gas-cooled reactors.Microcrystalline graphite,as a near-isotropic raw material,has great advantages in the preparation of isotropic graphite.At the same time,microcrystalline graphite has high graphitization,high thermal diffusion coefficient and significantly lower thermal expansion coefficient than coke,and its stronger thermal expansion regulation mechanism than Mrozowski crack may make it have more excellent irradiation resistance performance.Therefore,this paper focuses on microcrystalline graphite to optimize the preparation process and properties of microcrystalline graphite-based isotropic graphite,and to develop the potential of microcrystalline graphite in the preparation of high-performance nuclear graphite.The performance of both matrix graphite and microcrystalline graphite-based isotropic graphite for high-temperature gas-cooled reactor spherical fuel elements needs to be further optimized.In this paper,we propose to use microcrystalline graphite as a raw material to replace artificial graphite in the matrix graphite and explore a new recipe to optimize the performance of the matrix graphite,which effectively improves the thermal conductivity and thermal expansion performance of the matrix graphite and provides a new idea for the performance optimization of spherical fuel elements.In addition,the preparation process of natural graphite was explored by using scaled graphite produced from Alashan League in Inner Mongolia as raw material,and the performance of the resulting natural graphite powder was verified,and the effect of spheroidization of natural graphite powder on the performance of matrix graphite was investigated.The microstructure and properties of microcrystalline graphite from two different origins were investigated to reveal the reasons for the differences in the properties of isotropic graphite prepared from the two raw materials and to achieve a preferential selection of raw materials.Then,the regulation of the internal pore structure of graphite was achieved through the design of aggregate particle size.The microcrystalline graphite-based isotropic graphite with a flexural strength of 41.7 MPa and anisotropy index as low as 1.01 was obtained,and its performance is better than that of commercial nuclear graphite IG-110.It provides a reference for the application of microcrystalline graphite-based isotropic graphite in nuclear engineering.