Carbon materials in a high temperature gas-cooled reactor pebble-bed module

Compared with the long use of carbon materials in human history, the debut of carbon materials in the Chicago Pile-1 nuclear reactor took place only 70 years ago. Since then, carbon materials have played important roles in nuclear reactors, especially in high temperature gas-cooled reactors (HTRs) because of their many excellent properties. As the most promising candidate for Generation IV reactors, a demonstration plant for HTRs, an HTR pebble-bed module (HTR-PM) is currently under construction in China. In the HTR-PM, carbon materials act as the core structural material, reflector, fuel matrix, moderator, and thermal and neutron shields. Because the dimensions and properties of the carbon are generally influenced by the high temperature and neutron irradiation in the HTR-PM, there are rigorous requirements for their performance. Since the precursor materials such as cokes and natural graphite, and the subsequent forming method play a critical role in determining the structure, properties and performance of the material under irradiation, a judicious selection of the raw materials and forming method is required to obtain the desired structure and properties. This paper introduces the detailed property requirements of different carbon materials in the HTR-PM and their fabrication processes. In addition, the current status and future commercialization of the HTR-PM in China and abroad are presented. In order to meet the requirement of full local production in a commercial HTR, long-term considerations such as the sustainable and stable supply of the raw materials, optimization of the manufacturing process in the local production of nuclear graphite for structural graphite and graphite pebbles, and the stable production and reduced cost of the precursor materials are discussed. Finally, current progress and future arrangements for the irradiation testing of Chinese nuclear graphite at the Oak Ridge National Laboratory (USA) are presented. This manuscript is intended to act as a reference for carbon material producers who intend to develop nuclear graphite and carbon materials for use in future commercial HTRs. Meanwhile, a great deal of information introduced in the manuscript is also useful for scientific researchers of carbon materials.