Advanced nuclear fuel element performance: ex-reactor verification and in-service evaluation technologies

The fuel assembly is a core component of nuclear reactors, whose performance directly impacts the economics and safety of nuclear power systems, as well as key performance indicators of nuclear power installations. Within the harsh operating environment of a nuclear reactor—characterized by high temperature, high pressure, intense radiation, and long operational lifespan—the safe operation of nuclear fuel elements faces significant challenges. Therefore, the development of advanced nuclear fuel technology remains a critical strategic priority for leading nuclear power nations worldwide. In particular, out-of-pile verification and in-service performance evaluation techniques for nuclear fuel elements represent key research focuses and challenges in the field. To support the research and development needs of China’s independent advanced nuclear fuel programs, several key experimental facilities have been established at Xi’an Jiaotong University. These include a flow-induced vibration test bench for 5×5 fuel assemblies, a full-scale fuel rod crud deposition and corrosion test facility, a fuel assembly lower tie plate debris filter test rig, and a test platform for deformation behavior of sodium-cooled fast reactor fuel assemblies. Through these facilities, essential performance data have been obtained, including flow-induced vibration characteristics of China’s proprietary fuel designs, crud deposition and corrosion behavior on cladding surfaces, debris filtration performance of lower tie plates, and core-level thermal deformation characteristics of fast reactor fuel assemblies. By establishing a series of out-of-pile experimental platforms, the simulation of key nuclear fuel phenomena has been achieved externally, replacing in-pile experiments and reducing the costs associated with experimental research for nuclear fuel performance evaluation and design improvements. Furthermore, a multi-dimensional, multi-physics coupled analysis platform for nuclear fuel elements, named BEEs and based on the finite element method, has been developed. This platform supports design analysis for a wide range of fuel types, including conventional rod-type fuel, accident-tolerant fuel (such as Cr-coated cladding and SiC cladding), annular fuel, plate fuel, helical fuel, spiral-rib fuel, TRISO dispersed fuel, and heat pipe reactor fuel. The implementation of refined geometric modeling for nuclear fuel elements and assemblies has significantly improved simulation accuracy, enabling precise characterization of key nuclear fuel phenomena. Furthermore, large-scale parallel computing has been leveraged to fully utilize computational resources, resulting in a substantial enhancement of computational efficiency. In addition, by establishing multiphysics coupling interfaces with open-source neutronics code OpenMC and in-house subchannel code SACOS, among others, the BEEs platform enables coupled neutronics-thermal-mechanical-fluid simulations. It provides technical support for the fuel design and development of advanced pressurized water reactors, gas-cooled microreactors, heat pipe reactors, and other reactor types. The development of nuclear fuel performance analysis software and the establishment of simulation platforms have propelled the construction of numerical reactors, enhanced nuclear fuel analysis efficiency, and played a vital role in fuel performance assessment and design optimization.