核动力工程

Research on Construction Method of a Machine Learning-Based Fuel Rod Temperature Distribution Surrogate Model

Liu Zhenhai, Qi Feipeng, Zhou Yi, Li Yuanming, Li Wenjie, Zeng Wei, Xin Yong, Wang Haoyu, Ma Chao

2023, 44(S2): 1-5. doi: 10.13832/j.jnpe.2023.S2.0001

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Abstract:
In order to improve the computational efficiency of large-scale fuel rod performance simulation, the construction method of fuel rod temperature distribution surrogate model (referred to as "surrogate model") is studied by taking fuel rod temperature prediction as an example. The calculation results of the fuel rod performance analysis code COPERNIC are used as the data source, and the representative training data are selected by using the k-means clustering algorithm. Four fully connected feedforward neural networks are trained to predict the outer surface temperature of the cladding considering the effects of coolant flow heat transfer and oxide film growth, the radial temperature distribution of the cladding, the outer surface temperature of the fuel pellet considering the effects of the gap variation between the fuel pellet and cladding, and the radial temperature distribution of the fuel pellet. By combining these neural networks, the temperature distribution of the fuel rod at different times can be quickly predicted based on the input fuel rod power history. Numerical experiments show that the calculation speed of the surrogate model is about 204 times faster than that of the COPERNIC code, and it has high accuracy. The mean deviations of fuel cladding and pellet temperature prediction on the whole data set are about 0.07°C and 0.44°C respectively.

Three Dimensionnal Simulation Investigation of Wedged Pellet-Clad Interaction Problem in Fuel Rod

Ma Zhengqing, Pang Hua, Zhang Kun, Tang Changbing, Wu Zhouzhi, Yan Feng, Xing Shuo

2023, 44(S2): 6-10. doi: 10.13832/j.jnpe.2023.S2.0006

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Abstract:
The pellet-clad interaction (PCI) is one of the reasons leading to breach of cladding. The fracture generated by pellet cracking could wedge into the gap between pellet and caldding, resulting the wedged PCI problem. This problem may cause the local stress of the cladding to exceed the limit value and increase the risk of cladding damage. In order to evaluate the influence of wedged PCI on the performance of fuel rods, a three-dimensional finite element fuel element performance analysis method was established based on MOOSE, a multi-physical coupling finite element platform. In this method, the radiation effect and thermal-mechanical coupling effect are considered comprehensively, and the numerical simulation of wedged PCI problem is completed for the single pellet model. The results show that the wedged PCI problem can change the temperature distribution, stress distribution and strain distribution of the cladding, increase the maximum Mises stress and equivalent creep strain of the cladding, and increase the risk of fuel rod failure.

Research on Thermal-fluid-structure Coupling Behavior for U-10Mo/Al Fuel Assemblies under Irradiation

Yuan Pan, Wang Haoyu, Huang Shan, Liu Menglong, Yue Ti, Ren Quanyao, Qin Mian, Zheng Lele, Guo Zixuan

2023, 44(S2): 11-16. doi: 10.13832/j.jnpe.2023.S2.0011

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Abstract:
In order to investigate the effects of in-pile mechanical deformation under irradiation on the mechanical and thermal-hydraulic characteristics of U-10Mo/Al fuel assemblies, the mechanical behavior and thermal-hydraulic behavior of U-10Mo/AI fuel assemblies under in-pile irradiation are studied by using the thermal-fluid-structure coupling analysis method under irradiation. By introducing non-uniform irradiation conditions into the irradiation-thermal-mechanical coupling behavior of the 3D finite element model for fuel assemblies, the distribution and evolution laws of structural mechanics field and temperature field of U-10Mo/Al fuel assemblies under time-dependent and location-dependent irradiation conditions are studied. The results show that under the coupling effect of flow field, temperature field, and mechanical mechanics, U-10Mo/AI fuel assemblies exhibit typical mechanical deformation behavior, and both support plates and fuel elements have a certain degree of bending; the temperature field of fuel assemblies show a typical feature of non-uniform spatial distribution, and the peak temperature occurs at the position of maximum swelling of the fuel element; the stress at the sides and corners of the pellet for cladding and the pellet is larger than that in the central region and support plates.

Research on Few Group Cross-Section Generation Method For Fast Reactor Based on Monte Carlo Code

Xiao Peng, Luo Qi, Xia Bangyang, Zhang Guangchun, Yao Dong, Zhou Yajing, Fang Chao, Li Tianya

2023, 44(S2): 17-22. doi: 10.13832/j.jnpe.2023.S2.0017

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Abstract:
In order to improve the accuracy of neutronics analysis for fast reactors and solve the complex resonance problem faced by traditional deterministic method in making few group cross-sections of fast reactors, this paper, based on the two-step method of assembly homogenization-core transport calculation, studies the method of assembly homogenized few group cross-section by using the Monte Carlo code from the aspects of anisotropic scattering, energy group structure and leakage correction. The numerical results show that the resonance effect of medium-mass nuclides can be well treated in the fast reactor few group cross-section generation based on the Monte Carlo code; the effects of anisotropic scattering can be effectively considered with 1-order scattering cross-section or transport modified few group section. Core effective multiplication factor ( k_eff ) may decrease due to the decrease in the number of energy groups of few group cross-section; core k_eff may increase due to the leakage correction. When Monte Carlo code is used in few group cross-sections generation of fast reactor, the k_eff deviation of core transport is less than 100 pcm (1pcm=10⁻⁵), and the power distribution deviation is less than 2%.

Study on Fast Calculation of High-accuracy Radiation Field Based on Response Matrix Method

Li Wenhan, Zhang Hongyue, Ying Dongchuan, Tian Chao, Wen Xingjian, Wang Shuang, Tang Shihan

2023, 44(S2): 23-28. doi: 10.13832/j.jnpe.2023.S2.0023

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Abstract:
To solve the problem that traditional transport calculation methods cannot take into account both rapidity and accuracy, and to realize the rapid iteration of radiation protection optimization and shielding optimization design, a fast calculation method of high-accuracy radiation field based on response matrix is developed. The biological shielding deep penetration fast calculation method based on response matrix and the surface source continuous calculation method based on SOURCE sampling technique are adopted. The calculation process of radiation field from the incident source of the biological shield to the outer space of the biological shield is divided into the calculation process of particle transport in the biological shield structure and the calculation process of particle transport in the outer space of the biological shield, so as to realize the rapid and high-precision dose radiation field analysis in the complex dynamic scene of the reactor unit. The calculation efficiency is 100 times higher than that of Monte Carlo (MC) direct calculation method. The results of this study can provide effective and reliable design methods and tools for personnel radiation dose optimization design and shielding structure optimization iteration under complex irradiation conditions.

Optimization Development of Online Monitoring System Depletion Calculation Based on Parallel Technology

Guo Fengchen, Gao Lulu, Lu Wei, Zhao Dehua, Yu Yang, Xu Ruijie, Ma Yongqiang, Wei Tong

2023, 44(S2): 29-32. doi: 10.13832/j.jnpe.2023.S2.0029

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Abstract:
In order to improve the calculation efficiency of the DESCAR module of the online monitoring system program when the number of depletion zones is large, the DESCAR module is optimized and reconstructed by using the parallel technology of Open Multi-processing (OpenMP) and Message Passing Interface (MPI) to improve the calculation efficiency of the online monitoring system program. The verification results show that the optimized and reconstructed DESCAR module can effectively improve the calculation speed of the online monitoring system program while ensuring the correctness of the calculation results, and the acceleration effect is remarkable, which meets the requirements of the real-time online monitoring system.

Remaining Useful Life Prediction of Rolling Bearings Based on Attention Mechanism and CNN-BiLSTM

Fu Guozhong, Du Hua, Zhang Zhiqiang, Li Qingzhao, Huang Siyu, Liu Yanting

2023, 44(S2): 33-38. doi: 10.13832/j.jnpe.2023.S2.0033

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Abstract:
Aiming at the problem that traditional deep learning methods do not have high accuracy in predicting the remaining useful life (RUL) of rolling bearings, a hybrid RUL model (CNN-BiLSTM-AM) based on attention mechanism convolutional neural network and bidirectional long short-term memory network is proposed, and the model is used to predict the RUL of rolling bearings. Firstly, the bearing first prediction time (FPT) is determined by the steepness characteristics of the bearing’s original vibration signal. Secondly, the noise reduction and normalization of the original vibration signal after FPT are carried out, and the RUL of rolling bearings under two different conditions is predicted by the hybrid model CNN-BiLSTM-AM. Finally, the hybrid model CNN-BiLSTM-AM is compared with several traditional models. The results show that the hybrid model CNN-BiLSTM-AM is more effective for the RUL of rolling bearings and has generalization performance.

Numerical Simulation Research on Heat Transfer and Flow Characteristics of Spiral Curled Fins

Xiao Guanfei, Chen Fucai, Tan Bo, Gan Bin, He Zhen, Xian Xirui, Liu Yize, Chen Hao, Du Hua

2023, 44(S2): 39-43. doi: 10.13832/j.jnpe.2023.S2.0039

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In order to gain a deeper understanding of the convective heat transfer capability of spiral curled fin heat exchanger, this paper conducts a study on the convective heat transfer characteristics of spiral curled fin heat exchanger in air from two aspects: heat transfer flow and the compactness of the heat exchanger, using numerical simulation methods. The effects of dimensionless tube spacing (T/D), dimensionless fin height (H/D), and dimensionless fin spacing (S/D) on the heat transfer and flow characteristics of spiral curled fins were studied. The research results indicate that a smaller T/D will increase the flow capacity of the finned tube bundle, thereby increasing convective heat transfer. With the increase of H/D, the heat transfer area of the spiral curled fin tube bundle increases, and the total heat transfer increases. However, the heat dissipation is not sufficient, which affects the efficiency of the spiral curled fins. When the S/D is large, the compactness of the spiral curled fins decreases, the resistance of the tube bundle decreases, and the average volume heat transfer density also decreases. The research results of this article have obtained the influence of different parameters on the heat transfer and flow characteristics of spiral curled fins, which has good guiding significance for the design of spiral curled fins.

Numerical Simulation Research on Three-dimensional Temperature Field and Flow Field at the Top of Reactor under Natural Convection Conditions

Tang Xiangdong, Li Wei

2023, 44(S2): 44-49. doi: 10.13832/j.jnpe.2023.S2.0044

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There are many equipment at the top of reactor in PWR, and the temperature and flow fields are complex. In order to evaluate the feasibility of cooling the control rod drive mechanism (CRDM) by natural convection, based on FLUENT software, the numerical simulation of the reactor top structure under natural convection conditions was carried out, and the flow field, temperature field distribution and the maximum coil temperature rise under four conditions were obtained. The simulation results show that under different operating conditions, the heat generated by CRDM operation can be completely taken out of the pit by natural convection, and there is no pit heat. The coil temperature of the CRDM will not exceed its operating temperature limit. This research can provide an important basis for cooling the CRDM using natural convection.

Floating Raft Vibration Isolation Design and Sensitivity Analysis of Raft Parameters for Pumps in Reactor System

Wang Yu, Cai Longqi, Lai Jianyong, Li Yang, Wei Bo, Wang Ran, Liu Shuai

2023, 44(S2): 50-54. doi: 10.13832/j.jnpe.2023.S2.0050

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Abstract:
Pump equipment in reactor system is an important source of vibration and noise for marine nuclear power plant. At present, single-layer vibration isolation measures are mostly adopted in practical engineering, and the damping effect is limited. In order to meet the new requirements of vibration and noise control, floating raft isolation technology has been introduced. However, the floating raft isolation technology in the reactor system has just started, and it still stays on a simple raft structure that meets the basic layout and vibration reduction requirements. There is little research on the structural parameters of the raft itself. This article is the first to carry out diversified structural design of raft structures for reactor system pumps. Three different raft structures are proposed and their comprehensive performance is compared. The characteristics of different raft structures are mastered, and parameter sensitivity research is conducted on the plate raft that has good low-frequency vibration reduction effect. The influence of raft stiffness parameters and mass parameters on the vibration reduction effect of floating raft isolation systems is obtained, which provides theoretical support for the selection and design of floating raft structures for reactor system pumps.

Reasearch and Optimization Analysis of Vibration Model of Recipirocating Pump Pipeline Based on Fluid-solid Coupling

Li Yang, Liu Jia, Cai Longqi, Lai Jianyong, Lu Tong, Wang Yu, Gan Yiran, Chen Jiu

2023, 44(S2): 55-60. doi: 10.13832/j.jnpe.2023.S2.0055

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Abstract:
In view of the excessive vibration of the outlet pipeline system of marine reciprocating pump, the fluid-solid coupling analysis method was used to establish the system-level vibration transmission characteristics analysis model applicable to the outlet pipeline with the field test data, and the vibration response characteristics of the pipeline system were analyzed by using the established model. Based on the methods of modal matching and vibration node coupling, the design principles for optimal arrangement of pipeline hangers and parameters were put forward, and the sensitivity analysis of hanger types and parameters was carried out. The analysis results show that the peak vibration displacement and peak velocity of the pipeline are significantly reduced after the optimization of pipeline hanger arrangement, and the average vibration acceleration level at the base is 3.48dB lower than that before optimization.

Research on Simulation Approach of Inter-wrapper Flow in Liquid Metal Cooled Fast Reactor Based on Subchannel Method

Liang Yu, Wang Xiaoyu, Deng Jian, Liu Yu, Song Gongle, Zhong Ruicheng, Zhang Dalin, Zhu Dahuan

2023, 44(S2): 61-66. doi: 10.13832/j.jnpe.2023.S2.0061

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In order to explore the conjugate heat transfer effect of the coolant between the assmblies and inter-wrapper channels, the subchannel method is applied to provide a new simulation approach for the inter-wrapper flow (IWF). The subchannel model of IWF is solved based on the stable and efficient SIMPLE algorithm to address the issue that the classical subchannel algorithm is difficult to converge in the face of low flow, reverse flow and backflow phenomena. Through the 3-subassembly test using sodium working fluid (CCTL-CFR), the reliability of the subchannel simulation method for IWF is demonstrated by comparing the temperatures of the coolant and wall. Taking the typical liquid metal cooled fast reactor as the object, the thermal-hydraulic analysis of the full core is conducted. It is found that IWF can greatly flatten the radial temperature distribution of the core and reduce the temperature peak value, which proves the necessity of considering the effect of IWF in thermal-hydraulic analysis. This study provides a feasible analysis method for the thermal and safety analysis of liquid metal cooled fast reactors.

Analysis of Start-up Characteristics of Heat Pipe Reactor

Du Zhengyu, Ma Yugao, Zhong Ruicheng, Ding Shuhua, He Xiaoqiang, Deng Jian, Liu Yu

2023, 44(S2): 67-73. doi: 10.13832/j.jnpe.2023.S2.0067

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Abstract:
The heat pipe reactor differs significantly from the pressurized water reactor in terms of neutron energy spectrum, fuel and core structure, temperature feedback coefficient, reactivity control method, and coolant, which may lead to a large power peak in the core and temperature difference at both ends of the heat pipe during startup. In response to these issues, this paper focuses on the land-based heat pipe reactor and proposes a “leapfrog” startup control strategy. The control set values of the strategy are determined through theoretical analysis. In terms of system design improvement, a scheme is proposed to add an air preheater for preheating the condensation section of the heat pipe before the heat pipe is completely started. The application effect of the aforementioned scheme is analyzed and verified using numerical calculations. The results show that the startup control strategy and system design improvement proposed in this paper reduce the fluctuation amplitude of core power during startup, decrease the temperature difference between the evaporation and condensation sections of the of heat pipe during startup, and correspondingly reduce the thermal stress of the heat pipe, thereby improving the reliability of heat pipe operation. The research findings of this paper provide input for drum control design and serve as a reference for setting monitoring parameters related to reactor protection and control systems. The relevant research findings of this paper can also provide reference for the design of gas-cooled systems in heat pipe reactors.

Validation and Analysis of Two-group Interfacial Area Transport Model for Rectangular Channel

Yu Yang, Lu Wei, Wang Wenlin, Song Xiaoming, Zeng Hui, Guo Fengchen, Li Zhongchun, Sun Zibin

2023, 44(S2): 74-79. doi: 10.13832/j.jnpe.2023.S2.0074

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Abstract:
In order to demonstrate the accuracy and applicability of the two-group interfacial area transport model for rectangular channel, the transport characteristics of gas-liquid two-phase interface in rectangular channel under vertical condition were experimentally studied by using four-probe conductivity probe measurement method, and a large number of experimental data such as time-average void fraction and interfacial area concentration were obtained. The experiment was conducted in normal temperature and pressure with water and air as the working medium. The test sections of the channel were made of transparent acrylic material with a cross section of 10 mm×200 mm, and converted velocities of gas and liquid were 0.047-2.014 m/s and 0.315-4.416 m/s, respectively. Flow patterns involve bubbly flow, cap-turbulent flow and churn flow. On this basis, eight experimental conditions were selected to verify the two-group interfacial area transport model for rectangular channel, and the bubble interaction mechanism affecting the interfacial area transport model was analyzed. The results show that the relative errors of bubble interfacial area concentration and void fraction in group 1 and group 2 are within 10%, which verifies the correctness of the two-group interfacial area transport model for rectangular channel.

Research on Sensorless Control Method of Synchronous Reluctance Special Motor Based on High-frequency Square Wave Voltage Injection

Liu Yiyi, Peng Renyong, Wang Zhaosu, Wang Chunlei, Chen Meiyuan, Yu Haitao, Tang Shihan

2023, 44(S2): 80-85. doi: 10.13832/j.jnpe.2023.S2.0080

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Aiming at the phenomenon that the position sensor of synchronous reluctance special motor is prone to failure or large error in rotor position detection under high temperature, high pressure and strong radiation, a sensorless control method is proposed to detect the position of synchronous reluctance special motor without relying on the position sensor. On the basis of vector control, the positive and negative alternating high-frequency square wave voltage signals are injected into the estimated d-axis, and corresponding high-frequency response current is generated in the estimated q-axis. The high-frequency response current contains the rotor position information of the motor. The rotor position information can be estimated through the rotor position observer, and the sensorless control of synchronous reluctance special motor can be realized. The simulation results show that the proposed method can achieve accurate control of the synchronous reluctance special motor under high temperature, high pressure and strong radiation conditions, and has the advantages of fast convergence, high accuracy and easy engineering implementation.

Design and Implementation of Static CRDM Power Supply System in Modular Small Reactor

You Zhou, Han Yong, Liu Feiyang, Liu Wenjing, Liu Yanan, He Zhengxi, Li Peng, Gao Yong

2023, 44(S2): 86-91. doi: 10.13832/j.jnpe.2023.S2.0086

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In order to meet the miniaturization, low noise, and easy maintenance requirement of modular small reactors for control rod drive mechanism (CRDM) power supply system, a static CRDM power supply scheme based on 12-phase low ripple thyristor rectification and super capacitor energy storage is proposed on the basis of comprehensive analysis and arrangement of the load demand of rod power supply system and the latest development of rectifier and energy storage technology. During the development and implementation of this scheme, researchers focus on electrical topology architecture, power electronic rectification and power energy storage technologies. After a series of analysis, research, design and experimental demonstration, it is proved that the new system scheme fully meets the requirements of the CRDM power system of the modular small reactor.

Research on Unloading Instruction Design Technology of Diesel Generators in HPR1000 Nuclear Power Plant

Wang Lin, Wu Qiaofeng, He Zhengxi, Liu Hongchun, Sun Shiyan, Li Yu, Chen Peng, Zhang Junqi

2023, 44(S2): 92-97. doi: 10.13832/j.jnpe.2023.S2.0092

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Engineered safety features actuation system is used to mitigate the consequences of accidents in nuclear power plants, which plays a vital role in the safety of nuclear power plants. The spurious triggering of unloading instruction of diesel generators may prevent the normal operation of engineered safety features. However, currently there are no clear design criteria and specific requirements for the mis-operation failure rate and mal-operation failure rate indicators for the unloading instruction of diesel generators. Therefore, an in-depth research on the design principles, reliability requirements and periodic test design of the unloading instruction of diesel generators is conducted based on the deterministic and probabilistic analysis. Then the design requirements for the unloading instruction of diesel generators are proposed, and the overall technical scheme for the unloading instruction of diesel generators is designed for the third generation nuclear power plant HPR1000. Finally, the fault tree and Markov reliability analysis methods are used for verification. The verification results show that the proposed design requirements are reasonable and the instruction design scheme has high reliability. This research provides an important reference for the design of subsequent nuclear power plant I&C system.

Research on Strong Dynamic Load Transfer Characteristics of Nuclear Pipe

Lu Xifeng, Wang Xinjun, Xiong Furui, Bai Xiaoming, He Feng, Li Bingjin, Yang Kang

2023, 44(S2): 98-103. doi: 10.13832/j.jnpe.2023.S2.0098

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A strain rate-depended elastic-plastic constitutive model is constructed based on the mechanical properties of main pipe material at different temperatures and strain rates. The main factors affecting the precision of elastic-plastic analysis method are obtained by simulation of pipe drop test, and an elastic-plastic dynamic load transfer analysis method based on the strain rate-dependent constitutive model is established. The dynamic response analysis of pipe is carried out by using this method, and the calculated results of response acceleration and stress are compared with the results of elastic analysis. The results show that the elastic-plastic analysis can effectively reduce the structural response. The method cannot only ensure the safety of structures under strong dynamic load, but also reduce the difficulty of structure design, and can be applied to the strong dynamic load transfer analysis of pipe system.

Investigation on Fluidelastic Instability of Square Tube Bundle Based on Dynamic Mode Decomposition Method

Feng Zhipeng, Xiong Furui, Zhao Xielin, Cai Fengchun, Zhou Jinxiong

2023, 44(S2): 104-108. doi: 10.13832/j.jnpe.2023.S2.0104

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The current study of fluidelastic instability mainly depends on macro-response, and there is no technical means to judge stability from a more essential level. In this study, the square tube bundle is taken as the object. Firstly, based on the three-dimensional fluid-structure interaction analysis model, the vibration response and fluid force characteristics of each tube are obtained, and the macroscopic response characteristics of the tube bundle are studied. Secondly, the dynamic mode decomposition (DMD) method is introduced to decompose and reconstruct the fluid-structure interaction system, and then the fluidelastic instability of the tube bundle is studied from the two aspects of macro response and DMD mode. The results show that DMD method can not only realize the rapid reconstruction and prediction of the dynamic characteristics of the flow field, but also accurately extract the dominant modes and frequencies of the unstable flow field, and judge the stability of the extracted modes. Combining with the macro response, this method can reflect the stability of the system more comprehensively.

Research on Reliability Evaluation Method of Nuclear Energy System Based on Dynamic Bayesian Network

Wei Wentao, Li Meifu, Zhu Dahuan, Zhong Mingjun, Guo Yongjin, Du Zhengyu, Jiang Xiaowei

2023, 44(S2): 109-114. doi: 10.13832/j.jnpe.2023.S2.0109

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Aiming at the problem that the reliability analysis of static system can not analyze the dynamic time sequence of the running system when the traditional fault tree analysis focuses on the design stage, a reliability analysis method based on dynamic Bayesian network (DBN) is proposed, which takes the dynamic fault tree as the bridge and obtains the DBN model from the fault tree. In this study, a typical PWR main water supply system is selected, and the reliability analysis, fault diagnosis and sensitivity analysis of the system are carried out by using DBN method. Compared with the traditional analysis method, the reliability data obtained is closer to the real value, which provides a more accurate basis for operation decision-making and can improve the economy of nuclear power plants.

Novel Measurement Method for Shear Failure Strength of Oxide Scales on Inner Surface of Supercritical Carbon Dioxide PCHE

Huang Junlin, Li Chao, Zhu Xiaoliang, Tu Yiyou, Xu Qinglan

2023, 44(S2): 115-119. doi: 10.13832/j.jnpe.2023.S2.0115

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The spalling of oxide scales formed on the inner surface of printed circuit heat exchanger (PCHE) seriously influences the safe and efficient operation of supercritical CO₂ Brayton cycle units. The existing prediction model for spalling is difficult to make accurate prediction because it lacks the key parameter of shear failure strength of oxide scale. To address this issue, an analytical model for the evolution of interfacial shear stress under tensile loading was established based on the assumption of elastic-linear hardening mechanics for the transition layer at the oxide scale/substrate interface. Then, a new method for measuring the shear failure strength of the oxide scale was proposed, which involved tensile loading tests combined with acoustic emission technology and specimens with oxide scales. The results indicate that the proposed method accurately predicts the evolution of shear stress at the oxide scale/substrate interface and determines the shear failure strength of the oxide scale without making any prior assumptions about the interfacial shear stress distribution. This method can provide key data for constructing the criterion and prediction model of oxide scale spalling on the inner surface of supercritical CO₂PCHE.

Research on CMFD Preconditioner for Two-dimensional MOC Krylov Subspace Iteration

Zhang Guangchun, Zhang Haochun

2023, 44(S2): 120-125. doi: 10.13832/j.jnpe.2023.S2.0120

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To improve the efficiency of the Krylov subspace iteration for two-dimensional method of characteristics (MOC), a preconditioner based on the coarse-mesh finite difference (CMFD) matrix is proposed. Firstly, the CMFD acceleration method is linearized and the linear CMFD preconditioner is derived. Secondly, the linear CMFD preconditioner is applied to the Krylov subspace method to solve the two-dimensional MOC equation. Finally, the acceleration performance of the linear CMFD preconditioner is tested using the IAEA LWR and 2-D C5G7 benchmarks. The results show that, after applying the CMFD preconditioner, the iteration count for the IAEA LWR benchmark is reduced by 52.7%, and the computational time is decreased by 41.8%. For the 2-D C5G7 benchmark, the iteration count is reduced by 20.3% and the computational time is reduced by 13.2%. The study also finds that the CMFD preconditioner works well for problems with weak local heterogeneities, but its performance decreases for problems with strong local heterogeneities.

Research on Hydraulic Performance of LFR Axial-flow Reacter Coolant Pump

Lyu Tianzhi, Yang Congxin, Guo Yanlei

2023, 44(S2): 126-132. doi: 10.13832/j.jnpe.2023.S2.0126

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In order to master the flow characteristics of lead-bismuth medium in axial-flow reactor coolant pump, the transient numerical calculation of lead-bismuth medium and water medium was carried out by computational fluid dynamics (CFD) method and shear stress transport (SST k-ω) turbulence model, and the energy changes and their laws of the two media in the calculation domain of impeller and guide vane were compared and analyzed. The research results indicate that the change in Reynolds number of the working medium has a significant impact on the hydraulic performance of the axial-flow reactor coolant pump, and the head and efficiency of the coolant pump with lead-bismuth medium are higher than those with water medium. The theoretical head of the coolant pump is basically the same under two different media, but the actual head with LBE medium is 3% higher than that with the water medium, indicating that the difference between the two media is mainly reflected in the flow loss. In the study of the hydraulic loss forms of two media, it was found that the wing loss caused by friction of the coolant pump with LBE medium is smaller than that with water medium, and the boundary layer separation point of LBE medium is significantly delayed. This study can provide some reference for the hydraulic design of the coolant pump of the lead-cooled fast reactor.

Conceptual Design and Physical Analysis of Multi-Purpose Heat Pipe Reactor Prototype

Li Panxiao, Zhang Zhipeng, Wang Chenglong, Zhang Dalin, Qiu Suizheng, Su Guanghui

2023, 44(S2): 133-139. doi: 10.13832/j.jnpe.2023.S2.0133

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To verify the feasibility of the multipurpose micro heat pipe reactor nuclear power technology, an integrated experimental device for multipurpose heat pipe reactor power system was designed. This experimental device utilizes high-temperature potassium heat pipes to achieve core cooling and energy transfer processes, employs Stirling engines and bismuth cobaltite thermoelectric modules to realize dynamic and static thermoelectric conversion processes. In this paper, the prototype core physical design of the reactor was carried out using the Monte Carlo code MCNP, which provides technical support for the completion of the heat pipe reactor prototype. The validation results indicate that 80% enriched UN fuel can meet the design requirements; the core neutron spectrum exhibits a fast neutron distribution; when more than two B₄C poisons are oriented toward the core, the reactor can be safely shut down; and the core power peaking factor is 1.37. This research can serve as a reference for the critical experiments of the heat pipe reactor prototype.

Optimization Research on Rapid and Accurate Underwater Positioning of Fuel Assemblies Based on SAM Pre-Trained Large Model Intelligent Combination Strategy

Chen Xiangyu, Li Hao, Wang Bingyan, Wang Kun, Wan Hao, Wen Xin

2023, 44(S2): 140-145. doi: 10.13832/j.jnpe.2023.S2.0140

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Accurate positioning of fuel assembly is the key to successful grasping and nondestructive lifting in the process of reactor refueling. Due to the high requirements for safety and efficiency, it is necessary to realize adaptability and reliability in a changeable environment while ensuring high accuracy in the face of complex underwater environment in the reactor, so as to realize full-automatic accurate positioning. In this study, the object rapid detection model (YOLO) is established, and the natural language processing-based SAM (Segment Anything Model) image segmentation pre-training large model is used for further segmentation. Finally, the post-processing optimization of target graphics is realized through a priori structure, and the positioning accuracy of fuel assembly is improved. This multi-stage combined strategy model achieves algorithmic interpretation of fully automated intelligent positioning process to meet the debugging requirements at the refueling site, while solving the instability problem in the underwater uncertain environment through fast detection-intelligent segmentation-post process to achieve high paradigm and robustness. In the simulated test environment, the model is fast, reliable and highly debuggable. The positioning time of a single assembly is less than 1s, the error is less than 0.5 mm, and the positioning efficiency of refueling is improved by more than 90%, allowing significant reduction of the irradiation dose of operator.

Analysis of Mixed Equivalent Magnetic Network Model of Reactor Control Rod Drive Mechanism Considering Magnetic Saturation

Yang Yun, Xu Qiwei, Zhao Yizhou, Fu Guozhong, Tang Jiankai

2023, 44(S2): 146-152. doi: 10.13832/j.jnpe.2023.S2.0146

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Abstract:
As an actuator for regulating the speed of neutron reaction in a nuclear reactor, the safety and reliability of control rod drive mechanism (CRDM) are very important. In this paper, a mixed equivalent magnetic network (MEMN) model is proposed, which can quickly and accurately calculate the dynamic electromagnetic characteristics of CRDM. The model combines the equivalent magnetic circuit (EMC) method with the reluctance network (RN) method to get a trade-off between accuracy and speed. The magnetic flux area correction factor is introduced to characterize the influence of the edge effect of air gap magnetic flux on air gap reluctance. The nonlinear problem of magnetic materials is solved by cyclic iteration method. Through the calculation of this model, the magnetic density distribution and coil inductance of CRDM under different conditions are obtained. This model is applicable to the rapid optimization design of CRDM and the research of control algorithms.

Study on Reactivity Disturbance Characteristics of SCO₂ Reactor Assembly Caused by Burnable Poisons

Zong Yi, Zhuang Kun, Lu Di, Qi Shengdong

2023, 44(S2): 153-159. doi: 10.13832/j.jnpe.2023.S2.0153

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Abstract:
In order to investigate the reactivity disturbance characteristics of supercritical CO₂ reactor assemblies caused by burnable poisons and to obtain a stable and safe reactivity control method, this paper puts forward 7 different burnable poison arrangement models of 2 categories. By studying the reactivity changes of assemblies under different burnable poison loading, the reactivity control methods by adjusting the consumption rate of burnable poisons are obtained according to different arrangements: 1) through the aggregation arrangement of mixing rods; 2) the reactivity can be well controlled by adjusting the H-ratio under a certain arrangement form and loading quantity. For example, when B₄C burnable poison with ¹⁰B enrichment of 3% is loaded with the H ratio of 17.5, the reactivity fluctuation is only 2600 pcm (1 pcm = 10⁻⁵). The influence of combustible toxicant on the reactivity perturbation of supercritical CO₂ reactor assembly is obtained and the reactivity control method is proposed.

Study on Thermal Stratification Characteristics of a New Pressurizer Surge Line

Yuan Yuan, Chen Cong, Zhou Yuan, Tang Bin

2023, 44(S2): 160-165. doi: 10.13832/j.jnpe.2023.S2.0160

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Abstract:
In order to relieve the stress of the lower space arrangement in the nuclear power plant, a new pressurizer design scheme with surge line and electric heating element water tank structure is proposed in this study, and the thermal stratification characteristics of the pressurizer surge line are discussed. The new pressurizer has a new water tank located in its upper part with an inserted horizontal electric heating element, and the surge line is connected from the upper head of the pressurizer to reduce impurities into the main loop. Aiming at the in-surge and out-surge scenarios of the new pressurizer surge line, the three-dimensional flow and heat transfer simulation of surge line is carried out by using FLUENT large eddy model with the analysis results of RELAP5 system as the boundary, and the thermal stratification distribution characteristics are obtained. The results show that the thermal stratification in the vertical direction of the flow section is more likely to occur in the horizontal section of the surge line, while the thermal stratification in the horizontal direction of the flow section is easy to occur at the pressurizer outlet. In both in-surge and out-surge scenarios, the maximum temperature difference of the cross section caused by thermal stratification in the surge line is within 9K, but the phenomenon of thermal fluid deposition occurs in the in-surge condition, resulting in long-term thermal stratification, therefore, the in-surge condition deserves special attention. The results of both conditions show that the thermal stratification of the new structure has little influence.

Research on Rod Position Calculation Method of Multi-coil Inductive Rod Position Detector Based on Principle of Segmented Coil

Gao Longjiang, Tang Jiankai, Fu Guozhong, Wang Yiming, Zhang Xuefeng, Wang Xiangyi, Luo Lingyan

2023, 44(S2): 166-170. doi: 10.13832/j.jnpe.2023.S2.0166

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Abstract:
Rod position detector is the main equipment for rod position detection in nuclear reactor, and its detection accuracy is very important to the safety and normal operation of nuclear reactor. Thus, this paper proposes a high precision rod position calculation method for multi-coil inductive rod position detector used in nuclear reactor. The structure and detection principle of multi-coil inductive rod position detector are analyzed, and the dynamic characteristics of multi-coil inductive rod position detector are also analyzed based on finite element method. The results show that the induced voltage of each segmented detection coil has a specific region, where the voltage peak value changes linearly. Based on this characteristic, a rod position calculation method of segmented coils of multi-coil inductive rod position detector is proposed. The peak value of each detection coil in the current cycle is collected in real time when the control rod moves at different positions, and then the rod position is calculated according to the relationship between the peak value of induced voltage and the rod position in the rod position calculation area. Finally, the theoretical analysis and rod position calculation method are verified by modeling with ANSYS and MATLAB/Simulink software. The simulation results show that the proposed rod position calculation method can achieve a detection accuracy of <0.2mm for rod position detector. The detection accuracy meets the requirements of high-precision rod position detection for control rod.

OpenFOAM Simulation and Verification of Droplet Separation in Baffles

Zhang Shen, Gui Nan, Yang Xingtuan, Tu Jiyuan, Jiang Shengyao

2023, 44(S2): 171-175. doi: 10.13832/j.jnpe.2023.S2.0171

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Abstract:
In order to predict the gas-liquid two-phase flow behavior in a baffle, OpenFOAM based Euler-Lagrangian method was used to simulate the two-way coupling flow of discrete and continuous phases in a baffle, with liquid droplets as the discrete phase and gas flow as the continuous phase. The discrete phase is subject to the drag force, and the continuous phase is simulated using the standard k-ε model and the standard k-ω SST model respectively. This article introduces grid meshing, post-processing of Lagrangian particle coordinates generated by OpenFOAM, and a program based on OpenFOAM for baffle steam water separation efficiency. The continuous-phase flow field, continuous-phase velocity field and steam water separation efficiency of different turbulence models under different grids are calculated and compared with the experimental data. The results show that the turbulence model has a greater impact on the results than the grid, whether it is continuous phase or discrete phase, and the calculation results of k-ω SST model are more accurate. The model can predict the separation efficiency of large diameter droplets accurately, but cannot predict the separation efficiency of small diameter droplets accurately enough.

Numerical Investigation of the Influence of Microchannel Diffusion Welded Heat Exchanger Head Structure on Flow Characteristics

Fei Junjie, Liu Minyun, Xi Dapeng, Tang Jia, Liu Ruilong, Zan Yuanfeng, Huang Yanping

2023, 44(S2): 176-183. doi: 10.13832/j.jnpe.2023.S2.0176

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Abstract:
In order to comprehend and grasp the influence mechanism of head geometry on the flow distribution capacity of microchannel diffusion welded heat exchanger (MCD) with supercritical carbon dioxide (SCO₂) as working fluid, optimize the head structure design of MCD, improve the flow distribution uniformity of heat exchanger, and thus improve the heat exchange efficiency and safety, this study employed numerical simulation methods to investigate the flow and flow distribution performance of MCD heads with different structures. To address the limitations posed by hardware conditions on the grid resolution of complex heat exchanger models, a user-defined function (UDF) code which can be widely used for simulating fluid dynamics performance in MCDs was developed, which can greatly reduce the repetitive grid-related tasks and lower the hardware threshold of simulation calculation. The software Fluent was used to analyze the influence of local geometric parameters of the head (different head wall curve parameters, different porous baffle parameters, etc.) on pressure drop, flow distribution performance and flow field. The results show that the vortex generated in the cavity of the inlet head and the abrupt contraction-expansion structure of the outlet head can cause pressure loss. The head featuring lower-height secondary curved wall can effectively suppress vortex generation and reduce pressure loss attributed to the abrupt contraction-expansion structure, subsequently lowering header pressure drop and enhancing flow distribution performance.tributed to abrupt contraction-expansion structures, thus reducing the head pressure drop and improving the flow distribution performance.

Thermal Performance Analysis of Low Temperature Differential Flow Heat Transfer Process in HFETR Irradiation Device

Liu Chang, Xia Yi, Peng Xingjie, Zhao Wenbin, Song Jiyang, Jin Shuai, Liu Runqi, He Yuhao

2023, 44(S2): 184-187. doi: 10.13832/j.jnpe.2023.S2.0184

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Abstract:
In this paper, a specific irradiation device in the High Flux Engineering Test Reactor (HFETR) is studied and analyzed. The Monte Carlo code is used to describe the heat release of different materials at different axial heights. The thermal model is established by using the code STAR-CCM+, and the accuracy of the model is verified by the measured data. Under given conditions, the deviation between the calculated temperature of thermocouple measuring point and the measured value is 2.3%. It is found that the temperature measurement deviation of 1%-4% may be caused in the process of low temperature differential flow heat transfer by changing the number and arrangement of thermocouples without considering the radial and axial position changes of the short tube of the plug assembly of the irradiation device. In this paper, the measurement deviation of low temperature difference flow heat transfer process in irradiation device is revealed, which can provide a key reference for improving the accuracy of temperature measurement and the safe operation and engineering design of HFETR.

Study on Fine Calculation of Deposition Source Terms in HFETR Test Loop

Xu Fei, Li Yao, Zhang Hangzhou, Li Li, Bi Shanshan, Gou Jiayuan, Zuo Wei, Wu Yao

2023, 44(S2): 188-192. doi: 10.13832/j.jnpe.2023.S2.0188

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Abstract:
It is of great significance to calculate the deposition source term produced by activated corrosion products in HFETR test loop for guiding dose estimation and decommissioning of facilities. In this paper, the test loop is divided into nodes and transport parameters are determined based on the CATE transport mechanism model and computation code. A 9-node transport model of the test loop is established to simulate the generation and distribution of activated corrosion product source terms of the test loop under actual operating conditions, and the results are compared with the actual monitoring data. The research results indicate that the calculation results of the model are consistent with the net effect of the migration direction of activated corrosion products, which proves the reliability of the calculated results. The dose rate error of the source term in the model is within 30% and the calculation results are conservative , which proves the accuracy of the calculated results. This study proves that the multi-node calculation method of the deposition source term in the test loop is applicable under the complex operating conditions of the test reactor and has great engineering application value.

Comparative Study on Corrosion Resistance of TaSiCN, TaAlSiCN and TaCrSiCN Coatings in NaCl-KCl Molten Salt

Ning Zhien, Wu Lu, Zhang Wei, Fang Zhongqiang, Mao Jianjun, Kong Xianggang

2023, 44(S2): 193-200. doi: 10.13832/j.jnpe.2023.S2.0193

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Abstract:
In order to explore the corrosion resistance of Al and Cr doped TaSiCN coatings in NaCl-KCl molten salt, nano-composite coatings of TaSiCN, TaAlSiCN and TaCrSiCN with approximately N atomic percent were prepared on Ta alloy substrate by using RF magnetron sputtering technology and adjusting the ratio of Ar and N₂ mixed gases. The microstructure, chemical composition and corrosion resistance of the coating in NaCl-KCl molten salt were systematically studied. The results show that all as-deposited coatings are composed of TaN, TaC and Ta(C,N) nanocrystals and amorphous carbon such as SiC_x, SiN_x, CN_x and sp2, among which the doped Al and Cr elements also exist in the coatings in amorphous form. After corrosion, the coating surface is mainly composed of crystalline components such as Ta(C,N), Ta₂O₅ and Na₂Ta₄O₁₁, and other amorphous components. The corrosion behavior of coating in NaCl-KCl molten salt is mainly oxidation corrosion, supplemented by molten salt corrosion. Through comparison, it is found that the order of corrosion resistance of three coatings is: TaAlSiCN > TaSiCN > TaCrSiCN. This study can provide a potential candidate coating material for the development of surface coating technology of molten salt electrolytic crucible.

Research on Deoxygenation Behavior of Sulfite Deoxygenation Resin

Li Xinzheng, Jiang Han, Dai Shuang, Cao Qi, Liu Dongbin, Li Mengxing

2023, 44(S2): 201-206. doi: 10.13832/j.jnpe.2023.S2.0201

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Abstract:
The deoxygenation performance of sulfite deoxygenation resin is closely related to its structure and adsorption kinetics thermodynamics. The study of deoxygenation mechanism can provide theoretical guidance for the subsequent optimization of resin. The microstructure of deoxygenation resin was characterized by infrared spectroscopy, scanning electron microscope and dispersion spectrum analysis, and the deoxygenation kinetics and thermodynamics of sulfite deoxygenation resin were studied. The microscopic characterization shows that the deoxygenation resin is a polystyrene sulfurous acid resin with carbon chain as the skeleton. The adsorption kinetic process of deoxygenation resin on the dissolved oxygen in aqeous solution conforms to the pseudo-second-order kinetic model, and there is chemical adsorption in the adsorption process of dissolved oxgen in water. The diffusion mass transfer model fitting showed that the main control step of the high-temperature deoxygenation resin was chemical reaction, and the main control step of sulfite deoxygenation resin transformed from anionic resin was liquid film diffusion. Gibbs free energy change (ΔG)<0, enthalpy change (ΔH)>0 and entropy change (ΔS)>0 of the deoxygenation resin indicate that its adsorption is a reversible spontaneous endothermic reaction, and increasing the temperature is beneficial to the adsorption. The research results in this paper can provide guidance for the performance optimization of deoxygenation resin.

Preliminary Research on Probabilistic Safety Analysis Technology of Space Nuclear Power Source

He Fang, Ding Hongchun, Liu Minghao

2023, 44(S2): 207-210. doi: 10.13832/j.jnpe.2023.S2.0207

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Abstract:
A preliminary study on the safety analysis technology of space nuclear power sources was conducted using the Probabilistic Safety Analysis (PSA) method to address a series of new issues brought about by the characteristics of weak redundancy and diversity, non-maintainability, high mobility, and experiencing multiple mission phases during their lifespan. Based on a thorough analysis of the special safety requirements of each mission phase, a comprehensive safety goal system suitable for space nuclear power sources was constructed. Research has shown that the safety assessment of space nuclear power sources still faces many technical challenges. For China, conducting safety assessment technology research on space nuclear power sources in parallel with the design phase will help improve the design efficiency and enhance the safety of space nuclear power sources.

Determination of Trace Arsenic, Plumbum, Stannum and Stibium in Nickel-Based Alloys by Inductively Coupled Plasma Mass Spectrometry

Luo Fengyan, Li Wenqiang, Zhang Qingyu, Wang Guohua, Guo Jinxuan

2023, 44(S2): 211-215. doi: 10.13832/j.jnpe.2023.S2.0211

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Abstract:
In order to accurately determine trace arsenic, plumbum, stannum and stibium in the nickel-based alloy (NBS), inductively coupled plasma mass spectrometry (ICP-MS) was used. The HNO₃-HCl system was used for airtight digestion of NBS, and the isotope mass numbers were selected as 75, 208, 120, and 121 respectively. The kinetic energy discrimination (KED) mode was used to overcome the mass spectral interference, and the internal standard element ⁸⁹Y was used to monitor the stability of the instrument and the matrix effect online. A method for the determination of arsenic, plumbum, stannum and stibium in nickel-based alloy was established. Under the optimized conditions, the signal intensities of each element had a good linear relationship with the corresponding mass concentrations, and the linear correlation coefficient was greater than 0.9999. When the sample weight was 0.1 g, the detection range of of the four elements was 10.0-200.0 μg/g. The detection limit of each element was better than 0.15 ng/mL, and the recovery rate of standard addition was between 85%-120%. The relative standard deviation (n=6) of the spiked sample was 2.8%-5.6%. This method has good sensitity, precision and accuracy, and can be used for the determination of arsenic, plumbum, stannum and stibium in NBS.

Determination of Trace Cadmium in Uranium Silicon Compounds by Graphite Furnace-Atomic Absorption Spectroscopy

Deng Dan, Luo Fengyan, Li Jie

2023, 44(S2): 216-220. doi: 10.13832/j.jnpe.2023.S2.0216

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In order to accurately measure the content of cadmium in uranium silicon compounds and provide reliable data for quality control and evaluation of nuclear fuel materials, graphite furnace-atomic absorption spectroscopy is used to study the determination of cadmium in uranium silicon compounds. By exploring the dissolution condition, the best parameter conditions of the instrument and the matrix influence behavior, the best experimental parameters were obtained, and the precision and addition recovery experiments were carried out. The experimental results show that when the detection range of the mass fraction of cadmium is 0.1-1.0 µg/g, the recovery rate of the method is 87%-110 %, and the relative standard deviation is better than 15%. This method is accurate and convenient, meeting the determination of trace cadmium in uranium and silicon compounds, and can be used in scientific research or production.

Research on Primary Vacuum System Based on Ejector

Min Jidong, Li Jing, Hu Wensheng, Wu Xinzhuang

2023, 44(S2): 221-225. doi: 10.13832/j.jnpe.2023.S2.0221

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Abstract:
In order to solve the problem that when the reactor coolant pump of the reactor coolant system discharges dynamically or jointly, the auxiliary thrust bearing of the reactor coolant pump burns out due to the rapid pressure drop of the main system and the instantaneous sharp increase of the auxiliary thrust bearing load of the reactor coolant pump, according to the operation process of water filling and discharge of the main system of the unit, an additional vacuum system is proposed to meet the low water filling and discharge requirements of the main system after overhaul. The simulation results show that the primary circuit pressure can be pumped to 0.015 MPa(a) within 70 minutes and 0.01 MPa(a) within 90 minutes after the vacuum system is put into operation. A nuclear power plant carried out the promotion and trial of the vacuum pumping system in the subsequent overhaul. The results showed that the gas content of the primary loop of the nuclear plant was qualified at one time, and the major hidden danger of burning the auxiliary thrust bearing of the reactor coolant pump after start-up was successfully avoided. The reliability of the reactor coolant pump was significantly improved, and at the same time, the critical path of overhaul was saved for more than 10 h.

2023 Vol. 44, No. S2