GAO Ming¹ ，LU Zhenming^2，3，LU Anyuan³ ，YU Deshui¹ ，ZHAO Yongqian¹ ，GAO Tian³ ，LIU Bing²

1. China North Nuclear Fuel Co. ， Ltd. ， Baotou 014035， China；

2. Institute of Nuclear and New Energy Technology， Tsinghua University， Beijing 100084， China；

3. Hubei Key Laboratory of Coal Conversion and New Carbon Materials， School of Chemistry and Chemical Engineering，Wuhan University of Science and Technology， Wuhan 430081， China

Abstract

Significance The fuel elements used in pebble-bed high-temperature gas-cooled reactors (PB-HTRs) are graphite spheres containing thousands of Tri-structural isotropic (TRISO) coated particles, which are fabricated through quasi-isostatic pressing. The coating layer of the coated particles serves as the first barrier to guarantee reactor safety. Before fuel element compression, a compression buffer layer, composed of the same material as the matrix, is wrapped around the surface of the coated particles. This layer directly and effectively mitigates damage to the coating layer during the element production process, a step known as the overcoating process.

Progress China’s high-temperature gas-cooled reactors (HTRs) have evolved over more than four decades, from the 10 MW high-temperature gas-cooled reactor-test module (HTR-10) to the 200 MW high-temperature gas-cooled reactor pebble-bed module (HTR-PM). Correspondingly, overcoating technologies, a crucial part of nuclear fuel production, have progressed through multiple stages: basic research-level, laboratory-scale, pilot-scale, commercial demonstration, and commercialization. In terms of equipment structure, various types of overcoating equipment have been developed, including laboratory-scale onion-shaped and truncated-cone-shaped types, a meshed drum-type for commercial demonstration, and non-porous-drum and planetary types for large-scale commercial applications. The single-batch capacity has increased significantly, from 1 kgU to tens of kilograms. Meanwhile, the automation level, safety, and environmental friendliness of the equipment have been progressively improved while ensuring high product yield and quality. Advanced research methods, such as online analysis of particle shape and size, and numerical simulation, are used in equipment design, development, and process optimization, effectively accelerating progress and enhancing the effectiveness of research and development. So far, China's nuclear fuel overcoating technology has surpassed its international counterparts in productivity, product quality, and equipment automation and advancement through decades of dedicated efforts by several generations of R&D personnel.