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SSRN 2023年

作者： Guo, Jia Ming, Yang Zhao, Fulong Fang, Huawei Yin, Jingwei Tian, Ruifeng College of Nuclear Science and Technology Harbin Engineering University Harbin150001 China Heilongjiang Provincial Key Laboratory of Nuclear Power System & Equipment Harbin Engineering University Harbin150001 China Key Laboratory of Nuclear Reactor System Design Technology of China Nuclear Power Research and Design Institute Chengdu610000 China

Small nuclear reactor (SMR) system has many advantages, including low construction cost, short construction period and fast economic benefits. SMR has broad prospects in power supply in remote areas, small power grids, low-temperature heating, nuclear hydrogen production, seawater desalination, nuclear powered ships, etc. In order to study the hydraulics and thermal parameters of supercritical carbon dioxide as coolant in SMR, this paper developed a supercritical carbon dioxide reactor sub-channel analysis program based on Modelica language. Based on the sub-channel analysis method, the reactor coolant flow channel is divided in several control bodies, then the program calculates hydraulics and thermal parameters of each control body. In order to verify the correctness of the model and program, sub-channel program will calculate the axial temperature distribution, radial temperature distribution, coolant flow rate and power level under steady-state conditions. Then compare these calculations with KAIST MMR in Korea. In the transient characteristic analysis, this paper will analyze the reactor power increase, reactivity insertion and coolant flow loss accident, then evaluate the safety performance of the reactor. This paper relies on theoretical modeling and program development method, studying the sub-channel thermal hydraulic characteristics of steady-state and transient conditions, which provides theoretical reference and program support for the study of transient response characteristics and safety characteristics of supercritical carbon dioxide reactor. © 2023, The Authors. All rights reserved.

关键词： Temperature distribution

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Thermal-Hydraulic Characteristics of Helical Cruciform Single Rod Based on Cfd Investigation

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SSRN 2024年

作者： Chen, Yiwen Zhang, Dalin Jiang, Dianqiang Deng, Jian Zhang, Xisi Wang, Xinan Tian, Wenxi Qiu, Suizheng Su, Guanghui State Key Laboratory of Multiphase Flow in Power Engineering Shaanxi Key Laboratory of Advanced Nuclear Energy and Technology School of Nuclear Science and Technology Xi’an Jiaotong University Xi’an710049 China Nuclear Power Institute of China 328 Changshun Avenue Chengdu610213 China Science and Technology on Reactor System Design Technology Laboratory Nuclear Power Institute of China Chengdu610213 China China Institute of Atomic Energy Beijing611731 China

To increase power density in nuclear reactors, the helical cruciform fuel (HCF) is designed as a fundamental element. HCF takes advantages of strong mixing effects, self-supporting features, and strengthened heat transfer, potential to increase the fuel performance in nuclear reactors. In this paper, friction factor and heat transfer coefficient empirical correlations of HCF single rod cooled by water were proposed using a geometric dimensionless number based on numerical simulation. The velocity field, and temperature distribution were obtained to discuss influences of geometric sizes on the fuel performance. Finally, correlations with a geometric dimensionless number were validated with various cases, whose application conditions were also proposed and discussed. This paper provides a guide for study of heat transfer and fluid flow in helical structures, and a reference for establishment of reactor system model using helical cruciform fuels. © 2024, The Authors. All rights reserved.

关键词： Heat transfer coefficients

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Numerical Study on the Impact Characteristics of a Single Molten Lead Bismuth Droplet on Water

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SSRN 2024年

作者： Lin, Yue Zhang, Dalin Chen, Yutong Zhang, Xisi Deng, Jian Du, Peng Tian, Wenxi Qiu, Suizheng Su, Guanghui Department of Nuclear Science and Technology State Key Lab. of Multiphase Flow in Power Engineering Shaanxi Key Lab. of Advanced Nuclear Energy and Technology Xi’an Jiaotong University No.28 Xianningxilu Beilinqu Shaanxi Xi’an710049 China Institute of Reactor Engineering Technology China Institute of Atomic Energy Beijing102413 China Science and Technology on Reactor System Design Technology Laboratory Nuclear Power Institute of China Sichuan Chengdu610213 China

As an important link in the possible occurrence of steam explosions, the interaction between molten materials and coolant is of great significance for safety analysis in severe accidents of nuclear reactors. This study is based on the two-dimensional multiphase and multi-component fluid dynamics code ACENA to model the process of single molten lead bismuth droplet impacting a water tank and obtain the velocity changes of the molten droplet as it moves through the water tank. Furthermore, a sensitivity analysis of relevant factors such as the heat transfer area fraction and drag coefficient of the droplet is carried out. To verify models in ACENA, the computation results are compared to experimental data. It is demonstrated that the overall trend of the velocity curve acquired by the ACENA code during the interaction between a molten lead bismuth droplet and water is consistent with the experimental results. The droplet falling velocity increases with the increase in droplet temperature when the temperature of water is the same, and the droplet falling velocity increases with the increase of water temperature at the same droplet temperature. The simulation results by ACENA code for MFCI are in good agreement with experiments which verifies the accuracy of relevant models in ACENA. It can provide an effective means for safety analysis of nuclear reactors in china. © 2024, The Authors. All rights reserved.

关键词： Drops

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A Target Trajectory Prediction Method in Air Combat Based on Wavelet-Attention-GRU Under the Frenet Frame

A Target Trajectory Prediction Method in Air Combat Based on...

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2024 IEEE International Conference on systems, Man, and Cybernetics, SMC 2024

作者： Zhang, An Mao, Zeming Xu, Haiyu Fan, Qiucen Bi, Wenhao Yan, Yuwen School of Aeronautics Northwestern Polytechnical University Department of Integrated Technology and Control Engineering Shaanxi Xi'an710072 China Northwestern Polytechnical University National Key Laboratory of Aircraft Configuration Design Shaanxi Xi'an710072 China Shanghai Zhongchuan SDT-NERCCo. Ltd. Department of Mission System Shanghai201114 China

ISBN: (纸本)9781665410205

The target trajectory prediction method can assist pilots in situation awareness and provide support for decision-making to improve the capacity to gain the advantage during high dynamic within-visual-range air combat. Aiming at the problem of traditional methods based on the Cartesian frame, such as the low utilization of training data and the weak generalization, and the low accuracy of the existing time series prediction models, a target trajectory prediction method in air combat based on Wavelet-Attention-GRU under the Frenet frame is proposed. In this method, the air combat features are described via the spatial trajectory curve based on the Frenet frame;the target trajectory prediction model is established by combining the GRU network with the improved multi-head self-attention mechanism by adding wavelet transform. Finally, the one-to-one within-visual-range air combat dataset obtained via the high-fidelity air combat simulator is applied to train and test the trajectory prediction model. © 2024 IEEE.

关键词： Trajectories

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Experimental Investigation of Droplet Transient Behavior During Reflood Cooling Process of Single-Rod Channel

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SSRN 2023年

作者： Chen, Mingjing Chen, Deqi Liu, Haiong Liu, Hanzhou Zhong, Lei Deng, Jian Key Laboratory of Low-grade Energy Utilization Technologies and Systems Chongqing University Ministry of Education Chongqing400044 China Science and Technology on Reactor System Design Technology Laboratory Nuclear Power Institute of China Chengdu610041 China

The reflood process after a loss of coolant accident (LOCA) in a nuclear reactor involves complex two-phase flow with low pressure and flow rate, as well as boiling phase transition. Accurately predicting the transient behavior of liquid droplets during the dispersed flow stage is crucial for evaluating reactor accidents, including peak cladding temperature (PCT). However, existing prediction models for liquid droplets in dispersed flows are typically based on quasi steady-state annular flow models and do not account for transient behavior, such as the propulsion characteristics of the quench front during strong transient flooding processes, and the formation mechanism of large droplets. In this study, we present the results of a visualization experiment of reflood cooling in a single-rod channel to investigate the development mechanisms of droplet formation and fragmentation. We observe the evolution behavior of the vapor-liquid interface during the reflood process and quantitatively analyze the transient size distribution characteristics of the droplets. Based on these findings, the transient characteristics of the quench front propagation during reflood, Kelvin-Helmholtz (K-H) instability, hot wall ejection mechanisms for droplet formation, and aerodynamic and capillary breakup mechanisms for droplet breakage, as well as entrainment and evaporation of droplets under high-speed steam are considered. A prediction model for droplet transient behavior during single-rod channel reflood cooling is established, and the results are compared with experimental data. © 2023, The Authors. All rights reserved.

关键词： Cooling

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AN UNSUPERVISED LEARNING-BASED FRAMEWORK FOR EFFECTIVE REPRESENTATION EXTRACTION OF reactor ACCIDENTS

arXiv

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arXiv 2022年

作者： Li, Chengyuan Li, Meifu Qiu, Zhifang Science and Technology on Reactor System Design Technology Laboratory Nuclear Power Institute of China Chengdu Sichuan China

Compared to knowledge-based diagnostic systems, data-based methods tend to perform better in terms of speed and accuracy in diagnosing reactor accidents, and have significant advantages in terms of scalability of models. With the increasing use of high-precision system analysis programs in nuclear engineering, the number of high-fidelity computational data for accident simulation is exploding. Therefore, an algorithm that can achieve both automatic extraction of low-dimensional features from the data and guarantee the validity of the features is needed to improve the performance and confidence of the accident diagnosis system. This study proposes an autoencoder-based autonomous learning framework, namely Padded Auto-Encoder (PAE), which is able to automatically encode accident monitoring data that has been noise-added and with partially missing data into low-dimensional feature vectors via a Vision Transformer-based encoder, and to decode the feature vectors into noise-free and complete reconstructed monitoring data. Thus, the encoder part of the framework is able to automatically infer valid representations from partially missing and noisy monitoring data that reflect the complete and noise-free original data, and the representation vectors can be used for downstream tasks for accident diagnosis or else. In this paper, LOCA of HPR1000 was used as the study object, and the PAE was trained by an unsupervised method using cases with different break locations and sizes as the dataset. The encoder part of the pre-trained PAE was subsequently used as the feature extractor for the monitoring data, and several basic statistical learning algorithms for predicting the break locations and sizes. The results of the study show that the pre-trained diagnostic model with two stages has a better performance in break location and size diagnostic capability with an improvement of 41.62% and 80.86% in the metrics respectively, compared to the diagnostic model with end-to-end model st

关键词： Extraction

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Analysis of Transient Characteristics of Droplets in the Dffb Regime During Single-Rod Channel Reflood Experiment

SSRN

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SSRN 2023年

This study aims to explore the dynamic distribution and hydrodynamic characteristics of droplets during the highly transient process of reflood. However, the quasi-steady state analysis is generally adopted in the current study, ignoring the dependence of droplet formation and breaking mechanism in the Dispersed flow film boiling (DFFB) mechanism on the time-related historical behaviors such as the advance of the quench front. A series of reflood cooling visualization experiments of zirconium alloy high-temperature rod-shaped heating surface were carried out to achieve this research goal. The wall surface and fluid temperature history curves were recorded, and the parameters, such as the size and velocity of DFFB regime droplets, were quantitatively extracted by visual image processing technology. Based on the formation and breakup mechanism of droplets in the dispersed flow, the reasons for droplet size distribution and velocity change with input heat flux, initial wall temperature, inlet subcooling, and inlet flow rate are well analyzed and explained. At the same time, the experimental results also show a strong correlation between droplet behavior and the reflood process in time. This study can provide more detailed physical support for the subsequent development of droplet behavior models more suitable for the strong transient reflood process and the evaluation of existing models. © 2023, The Authors. All rights reserved.

关键词： Heat flux

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A Long-term Dependent and Trustworthy Approach to reactor Accident Prognosis based on Temporal Fusion Transformer

arXiv

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arXiv 2022年

作者： Li, Chengyuan Qiu, Zhifang Ma, Yugao Li, Meifu Science and Technology on Reactor System Design Technology Laboratory Nuclear Power Institute of China Chengdu610213 China

Prognosis of the reactor accident is a crucial way to ensure appropriate strategies are adopted to avoid radioactive releases. However, there is very limited research in the field of nuclear industry. In this paper, we propose a method for accident prognosis based on the Temporal Fusion Transformer (TFT) model with multi-headed self-attention and gating mechanisms. The method utilizes multiple covariates to improve prediction accuracy on the one hand, and quantile regression methods for uncertainty assessment on the other. The method proposed in this paper is applied to the prognosis after loss of coolant accidents (LOCAs) in HPR1000 reactor. Extensive experimental results show that the method surpasses novel deep learning-based prediction methods in terms of prediction accuracy and confidence. Furthermore, the interference experiments with different signal-to-noise ratios and the ablation experiments for static covariates further illustrate that the robustness comes from the ability to extract the features of static and historical covariates. In summary, this work for the first time applies the novel composite deep learning model TFT to the prognosis of key parameters after a reactor accident, and makes a positive contribution to the establishment of a more intelligent and staff-light maintenance method for reactor systems. Copyright © 2022, The Authors. All rights reserved.

关键词： Nuclear industry

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Analysis of Transient Characteristics of Droplets in the Dffb Regime During Single-Rod Channel Reflood Experiment

SSRN

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SSRN 2023年

作者： Chen, Deqi Chen, Mingjing Liu, Hanzhou Liu, Haidong Zhong, Lei Deng, Jian Key Laboratory of Low-grade Energy Utilization Technologies and Systems Chongqing University Ministry of Education Chongqing400044 China Science and Technology on Reactor System Design Technology Laboratory Nuclear Power Institute of China Chengdu610041 China

This study aims to explore the dynamic distribution and hydrodynamic characteristics of droplets in the process of strong transient reflood. However, the quasi-steady state analysis is generally adopted in the current study, ignoring the dependence of droplet formation and breaking mechanism in the Dispersed flow film boiling (DFFB) mechanism on the time-related historical behaviors such as the advance of the quench front. A series of reflood cooling visualization experiments of zirconium alloy high-temperature rod-shaped heating surface were carried out to achieve this research goal. The wall surface and fluid temperature history curves were recorded, and the parameters, such as the size and velocity of DFFB regime droplets, were quantitatively extracted by visual image processing technology. Based on the formation and breakup mechanism of droplets in the dispersed flow, the reasons for droplet size distribution and velocity change with input heat flux, initial wall temperature, inlet subcooling, and inlet flow rate are well analyzed and explained. At the same time, the experimental results also show a strong correlation between droplet behavior and the reflood process in time. This study can provide more detailed physical support for the subsequent development of droplet behavior models more suitable for the strong transient reflood process and the evaluation of existing models. © 2023, The Authors. All rights reserved.

关键词： Heat flux

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Vibration absorption of parallel-coupled nonlinear energy sink under shock and harmonic excitations

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Applied Mathematics and Mechanics(English Edition) 2021年第8期42卷 1135-1154页

作者： Jian’en CHEN Wei ZHANG Jun LIU Wenhua HU Tianjin Key Laboratory for Advanced Mechatronic System Design and Intelligent Control School of Mechanical EngineeringTianjin University of TechnologyTianjin 300384China National Demonstration Center for Experimental Mechanical and Electrical Engineering Education Tianjin University of TechnologyTianjin 300384China Beijing Key Laboratory of Nonlinear Vibrations and Strength of Mechanical Structures College of Mechanical EngineeringBeijing University of TechnologyBeijing 100124China

Nonlinear energy sink(NES)can passively absorb broadband energy from primary *** multiple NESs connected in parallel exhibit superior performance to single-degree-of-freedom(SDOF)*** this work,a linear coupling spring is installed between two parallel NESs so as to expand the application scope of such vibration *** vibration absorption of the parallel and parallel-coupled NESs and the system response induced by the coupling spring are *** results show that the responses of the system exhibit a significant difference when the heavier cubic oscillators in the NESs have lower stiffness and the lighter cubic oscillators have higher ***,the efficiency of the parallel-coupled NES is higher for medium shocks but lower for small and large shocks than that of the parallel *** parallel-coupled NES also shows superior performance for medium harmonic excitations until higher response branches are *** performance of the parallel-coupled NES and the SDOF NES is *** is found that,regardless of the chosen SDOF NES parameters,the performance of the parallel-coupled NES is similar or superior to that of the SDOF NES in the entire force range.

关键词： coupling influence nonlinear energy sink(NES) vibration absorption

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