Search

BackgroundHeat pipe cooled reactor (HPR) has many characteristics, such as reliability, inherent safety, small volume, modularity, and solid core. The nuclear fuel of solid core is seriously affected by high temperature, strong irradiation, and solid constraint when operating, which affect the heat transfer performance and mechanical properties of the core seriously. The stress and gap heat transfer caused by the contact between monolith and other components change nonlinearly with the increase of burnup, and they influence each other. Therefore, the coupled irradiation-thermal-mechanical behavior of the monolith is a complex multi-physics phenomena.PurposeThis study aims to develop a coupled irradiation-thermal-mechanical model to explore the characteristics of gap variation, heat transfer and mechanics during the lifetime of solid core.MethodsFirst of all, based on the geometric parameter and material of a typical solid core of HPR with fuel rod composed of UO2 pellets and 316 stainless steel cladding, a coupled irradiation-thermal-mechanical model was developed and applied to the finite element multi-physics field analysis software COMSOL. The calculation parameter settings mainly referred to the design parameters of the MegaPower reactor. Then, a thermal conductivity model changing with the increase of burnup for UO2, the gap heat transfer model and mechanical contact were introduced in the gaps in the solid core, and both irradiation-induced deformation effect including densification and fission product swelling, and creep effect of UO2 pellets and 316 stainless steel monolith were taken into account. Finally, the model was applied to calculating the typical HPR and the characteristics of gap variation, heat transfer and mechanics were analyzed.ResultsAnalysis results show that pellet temperature and creep of monolith and cladding increase after complete contact between monolith and cladding. A smaller average number of heat pipes around the fuel rod result in higher temperature and stress distribution in the nearby area, and the cladding in this area has a risk of creep failure during its lifetime caused by internal pressure of the fuel rod and contact pressure between the monolith and cladding.ConclusionsThe gap contact can affect the heat transfer and mechanical properties of the solid core of HPR, and even result in an increase in the risk of cladding failure.

BackgroundThe enrichment of nuclear fuel may significantly influence the fuel performance of a reactor.PurposeThis study aims to explore the effect of U3Si2-Al plate-type fuel enrichment on its performance,MethodsThe fuel performance analysis code BEEs-Plates, neutronics Monte Carlo code OpenMC, and the one-dimensional system analysis code ZEBRA were coupled together within the MOOSE (Multiphysics Object-Oriented Simulation Environment) framework. Then the coupling code was employed to conduct the multiphysics coupling calculation for JRR-3 (Japanese Research Reactor No.3) fuel assembly enriched at 15%, 20%, and 25%. The data exchange among the three codes were realized with the help of interpolation transfer method implemented in MOOSE. Additionally, neutron physical parameters and fuel performance parameters after 231 d of operation were analyzed when the average fuel consumption of the module was 125.71 GWd∙tU-1.ResultsThe calculation results indicate that the max power density of fuel assembly enriched at 25% is 18% higher than the assembly enriched at 15%. Due to the high thermal conductivity of aluminum, the temperature difference in the fuel assembly is almost negligible whilst there is a significant difference in the fast neutron fluence. The results of fuel temperature and fast neutron fluence show that the volumetric strain is more obviously affected by the fuel temperature. Specifically, the plastic strain of the assembly with 25% enrichment is approximately 40% higher than that of the assembly with 15% enrichment.ConclusionThe analysis results of this study suggest that the assembly with a higher enrichment is more prone to failure.

Safe and reliable energy supply is the key foundation for the development of unmanned underwater vehicle (UUV). Unlike land and space missions, underwater missions are more demanding on energy, which requires higher power level, longer operating time, faster response time, and better concealment. Heat pipe cooled reactor has the advantages of large power capacity, simple structure, easy control of reactivity, and rapid thermal response. The solid-state reactor core does not require coolant and relies entirely on heat pipes to dissipate heat, thereby providing good inherent safety, controllability and concealment. Therefore, heat pipe cooled reactor is considered as one of the most promising options for UUV energy supply. In this study, a conceptual design of Nuclear Silent Thermal-Electrical Reactor (NUSTER-100) was proposed to meet the energy requirement of China’s heavy ocean UUV research and development. 109 sodium heat pipes were arranged in the reactor core for passive cooling, and the thermoelectric generators (TEGs) were employed in the reactor to convert fission heat to electric power. A set of heat pipe cooled reactor system-wild mathematical and physical models were established, including core neutron physics model, core channel heat transfer model, heat pipe model, thermoelectric conversion model and cold junction heat transfer mode. Based on the efficient and robust numerical algorithm and modular modeling ideas, heat pipe advanced reactor transient analysis code HEART was developed with independent intellectual property rights, and the key modules of HEART were validated and verified by heat pipe experiment and thermoelectric power experiment. The steady-state, cold-start transient and reactivity insertion transient conditions of NUSTER-100 were calculated and analyzed by HEART, and the full power operation characteristics of NUSTER-100 were obtained. Steady-state performance of the NUSTER-100 indicates that the solid-state core has good temperature flattening ability. The surface temperature of the heat pipe is less than 1 300 K, and the average temperature drop of the TEG module in central channel is 724 K, which can produce an electrical power of 1 207.8 W. Based on the cold-start transient thermal-hydraulic analysis, a three-stage heat pipe cooled reactor start-up scheme with high safety was proposed, and the stability and safety of heat pipe reactor under reactivity insertion transient were evaluated. The results show that the three-stage heat pipe cooled reactor start-up scheme can improve the reactor start-up efficiency. This study can provide support for the development of UUV and heat pipe cooled reactor technology in China.