| The energy resources become more diversified and dispersed with the development of society. Sometimes the energy system is required to work without attendants to satisfy the demand for the extension of exploration areas (e.g. exploration of outer space, polar regions, etc.) or the development of national defense technologies. As a result, in this paper a conceptual design of a small modular fast reactor integrated with Alkali Metal Thermal to Electric Converter (AMTEC) units was proposed internationally in order to meet the reliability in power supplies subjected to extremes of operating conditions. Moreover, the coolant flow in the primary reactor system is achieved by natural circulation under normal power. As a result, the rotating machines in traditional thermal power plants such as mechanical pump and turbine are discarded in the design, so the reliability of the power generation devices is increased. Meanwhile, the maintenance requirements and the noise of machines are also decreased. The small modular reactor (SMR) mainly includes the core, the primary loop, the intermediate heat exchangers and the passive heat removal system. The thermoelectric conversion portion includes large scale AMTEC units, thermoelectric cells and heat pipe units. Finally, the SMR-AMTEC (Small Modular Reactor-Alkali Metal Thermal to Electric Converter) system is integrated by connecting the primary loop and thermoelectric conversion portion with intermediate loops.Three key technologies of the small modular fast reactor in the conceptual design were investigated in the paper. They are reactor core physical control technology based on rotating drums, the primary loop natural circulation technology under normal power and the heat remove technology based on natural circulation. The three technologies are preliminarily proved to be feasible according to the investigation of their operational behavior and characteristics. The main research results are as follows:The reactor core physical control technology based on rotating drums was proposed in the paper. It can be concluded that decreasing the number of fuel rings and active fuel length when the core equivalent diameter and total cross-sectional area of the coolant channel are unchanged can effectively decrease the pressure drop across the core. When the total fuel mass was constant, the influence of pellet radius, fuel pin length and the number of rings of fuel pins upon the effective multiplication factor keff, pressure drop across the core and heat transfer was analyzed. Additionally, the B4C absorber thickness and beginning-of-life excess reactivity under different numbers of rings of the fuel pins were studied when the assumed additional shutdown margin was different. The results show that the physical control technology is feasible.The primary loop natural circulation technology under normal power is proposed in the paper. A dynamic simulation model (nonlinear method) of natural circulation loop was established by using MATLAB/Simulink, and then the transient response and stability of the natural circulation loop were analyzed. The model was verified by using the experimental results and FLUENT simulation results of some related liquid metal loops. A linear stability analysis code for natural circulation was developed based on MATLAB besides the nonlinear method. The code was also verified by using the existing experimental results and simulation results. Furthermore, both nonlinear and linear method were used to analyze the factors that influence the stability of natural circulation, including the changing of thermal power, types of working fluid and loop geometry parameters. The results show that increasing power more slowly at the beginning would be better for reducing the flow oscillations and the time required to reach steady state. The Na-loop has larger critical Reynolds number and thermal power than LBE-loop and Pb-loop. Reducing the aspect ratio of loop or extending the loop cooling section length could increase the stability of natural circulation loop. Finally, the primary loop of SMR-AMTEC system was optimized according to the stability analysis results of natural circulation, meanwhile, the transient response and stability of primary loop was also studied.The heat removed technology based on natural circulation was proposed. A dynamic simulation model of coupled natural circulation loop (composed of primary loop and heat remove loop) was established based on the single natural circulation loop by using MATLAB/Simulink, and then the transient response and stability of the coupled loops were analyzed. FLUENT was used to validate the model. Then, the influence of power changing and intermediate heat transfer surface area on the stability of coupled natural circulation loop was analyzed by using the model. The results also show that increasing power more slowly at the beginning would reduce the flow oscillations and the time required to reach steady state. However, obvious flow oscillations are not observed in coupled natural circulation loops when the rate of power decrease is different. Meanwhile, the loop can be stabilized by increasing the area of the intermediate heat transfer surface. Finally, the transient response and stability of passive heat removal system of SMR-AMTEC was analyzed in the paper.The preparation technologies of three key components of the small multi-tube circulating AMTEC unit in the conceptual design were particularly developed. They are fabrication technology of porous TiN film electrode of AMTEC, the sealing technology of BASE (Beta"-Alumina Solid Electrolytes) components and the development and test technologies of wick components. The main research results are as follows:The porous TiN films, as the electrode material of AMTEC, were deposited by screen printing on α-Al2O3 substrate. The influence of the deposition conditions was evaluated. The TiN film was characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and conventional surface probes. The results show that nitridized at a temperature ranging from 900℃ to 1000℃ for 2～4 h, the TiN phase dominated the porous films with (200) as the preferential growth orientation. As the nitridation temperature increased, the average pore size decreased while the porosity increased. The conductivity depends on the nitridation temperature and time. For instance, an increase of the nitridation time resulted in an increase of the conductivity at 900℃; a decrease-increase of conductivity at 1000℃, and a decrease of conductivity at 1100℃, respectively. The porous TiN film with the highest conductivity of 1.43×105 S·m-1 could be obtained by nitridizing at 1100℃ for 2h.A Special sealing structure of "BASE-tantalum-α-Al2O3-tantalum" was designed for the sealing of the BASE components and stainless steel base. The active brazing material Ti(70)Cu(15)Ni(15) was used in the active brazing of BASE components. The influence of sealing temperature and vacuum on the sealing quality was studied. The sealing surface was characterized with scanning electron microscopy and helium leak detectors. The results show that the temperature should be increased/decreased slowly when it is close to the flow point of brazing material so that all the sealing materials have similar temperature. The pressure should be less than 10-3 Pa to avoid the oxidation of brazing material since it contains a lot of Ti. Tight-fitting BASE components with good hermeticity (leakage rate<10-10 Pa·m3/s) can be obtained by using high temperature active brazing method.The powder sintering and wire-cutting method were used to develop the wick components. An ethanol experimental loop was built to test the capillary force and flow of wick components. The results show that the wick components can provide driven force for the circulation of ethanol which proves the reliability of wick components. The pore size of wick has greater influence on the maximum pressure head of the components than the evaporator. The pressure head of the components can be increased, and the flow resistance can also be decreased when a small pore size wick and a high porosity evaporator are chosen for the wick components.In summary, a conceptual design of a SMR integrated with AMTEC power generation system was firstly proposed in this paper. A breakthrough in the key technologies of engineering R&D of the SMR-AMTEC system is obtained according to the key technologies investigations of both the reactor and converter device. This study has laid an important foundation for the SMR-AMTEC system engineering R&D. The SMR-AMTEC system can become an energy option for the development of society, the scientific exploration and national defense after further development. |
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