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  • NECP-Atlas中协方差数据制作模块的开发与验证

    分类: 核科学技术 >> 核科学与技术 提交时间: 2024-04-14

    摘要: 不确定度量化已经成为反应堆物理分析的普遍需求,核数据的协方差数据是开展不确定度量化的基础数据。在核数据处理程序NECP-Atlas中开发了协方差数据产生模块covar_calc,产生适用于蒙特卡罗程序的连续能量协方差数据库与确定论程序的多群协方差数据库。covar_calc可根据不同核数据在评价核数据库中的存储格式及不同的计算方法,分别处理评价核数据库给出的所有协方差数据,包括:平均裂变中子数、截面、次级粒子角度分布、裂变谱、共振参数、中子活化截面等数据的协方差数据。通过与核数据处理程序NJOY21中协方差数据制作模块的对比验证,表明NECP-Atlas制作的多群协方差数据库的精度与NJOY21相当,最大偏差小于0.1%。在此基础上使用蒙特卡罗计算程序NECP-MCX和不确定度量化程序NECP-UNICORN分别计算得到不同基准题的灵敏度系数,并分别结合连续能量协方差数据库和多群协方差数据库,利用“三明治公式”计算得到最终的不确定度。结果表明,基于NECP-Atlas制作的多群协方差数据库计算得到的不确定度具有与NJOY21相当的精度。连续能量协方差和多群协方差制作精确,满足蒙特卡罗程序和确定论程序使用需求。

  • 基于C5G7-MOX的中子输运计算方法比较及MOC参数敏感性初步分析

    分类: 核科学技术 >> 核科学与技术 提交时间: 2024-04-09

    摘要: 特征线方法(Method of Characteristics,MOC)因其具备强大的几何处理能力,且在计算过程中亦能兼顾计算成本和计算精度,被广泛应用于高保真数值模拟计算中。常见的输运计算方法除MOC外,还包括碰撞概率法(Collision Probability Method,CP)和界面流法(Interface Current Method,IC)等。本文从方法理论以及数值计算上将MOC、CP和IC进行比较分析,对于评估其在pin-by-pin计算中的能力尤为重要。同时在MOC计算中,不同的参数选择会对计算成本和计算精度产生影响,因此有必要进行敏感性分析以寻求最佳参数。本文首先将三种计算方法从原理上进行比较分析,再基于2D C5G7-MOX基准题完成了数值计算及MOC参数敏感性初步分析。计算结果表明:MOC在计算精度、计算效率和内存开销上均优于CP和IC。MOC的计算耗时和内存开销分别为23.9min和37.5MB,与参考解的相对误差仅为6.04×10-4。而CP和IC的计算耗时分别为MOC的56.7倍和15.6倍,内存开销分别为MOC的407.7倍和32.8倍。进一步通过参数敏感性分析发现:网格划分对计算内存开销以及计算时间的影响最大,极角的选择对计算精度的影响最大,并且给出一组建议参数:网格划分6×6,极角为GAUS且数目为2,方位角个数为30。该组参数的计算耗时为45.4min,内存开销为264.7MB,相对误差为5.9×10-5,归一化后的栅元均方根误差为0.00255。

  • Unveiling the Re, Cr, and I diffusion in saturated compacted bentonite using machine-learning methods

    分类: 核科学技术 >> 核科学与技术 提交时间: 2024-04-08

    摘要: The safety assessment of high-level radioactive waste repositories requires a high predictive accuracy for radionuclide diffusion and a comprehensive understanding of the diffusion mechanism. In this study, a through-diffusion method and six machine-learning methods were employed to investigate the diffusion of ReO4– , HCrO4– , and I– in saturated compacted bentonite under different salinities and compacted dry densities. The machine-learning models were trained using two datasets. One dataset contained six input features and 293 instances obtained from the diffusion database system of the Japan Atomic Energy Agency (JAEA-DDB) and 15 publications. The other dataset, comprising 15,000 pseudo-instances, was produced using a multi-porosity model and contained eight input features. The results indicate that the former dataset yielded a higher predictive accuracy than the latter. Light gradient-boosting exhibited a higher prediction accuracy (R2= 0.92) and lower error (MSE = 0.01) than the other machine-learning algorithms. In addition, Shapley Additive Explanations,Feature Importance, and Partial Dependence Plot analysis results indicate that the rock capacity factor and compacted dry density had the two most significant effects on predicting the effective diffusion coefficient, thereby offering valuable insights.

  • 一价铜离子掺杂无铅钙钛矿Cs2AgBiBr6对晶体结构和电学性能影响第一性原理模拟研究

    分类: 核科学技术 >> 核科学与技术 提交时间: 2024-04-08

    摘要: 无铅双钙钛矿Cs2AgBiBr6作为环境友好型材料受到了核辐射探测领域的广泛关注,实验上发现对Cs2AgBiBr6进行Cu+掺杂能够显著提高材料稳定性与光电转换率。目前Cu+掺杂Cs2AgBiBr6的影响还未得到理论系统研究,本文基于第一性原理,采用密度泛函,开展了Cu+掺杂Cs2AgBiBr6对结构和电学性能影响的模拟研究。研究结果表明,Cu+掺杂会提高Cs2AgBiBr6的稳定性。掺杂形成的Cs2Ag1-xCuxBiBr6与原始材料Cs2AgBiBr6皆为间接带隙半导体,并随着Cu+掺杂比例提高能带间隙会显著缩短。根据态密度图分析,能带间隙缩短是由于Cu+掺杂会导致由Bi6p轨道主导的导带底部下移。Cs2Ag1-xCuxBiBr6相比Cs2AgBiBr6具有更高的稳定性与更优的电学性能,可作为半导体辐射探测器的候选材料。

  • Two-dimensional Particle-in-Cell modeling of blow-off impulse by X-ray irradiation

    分类: 核科学技术 >> 核科学与技术 分类: 核科学技术 >> 辐射物理与技术 提交时间: 2024-04-05

    摘要: Space objects, such as spacecraft or missiles, might be exposed to intense X-rays in outer space, leading to severe damage. How to reinforce these objects to reduce damage from X-ray irradiation is a significant concern. Blow-off impulse (BOI) is a crucial physical quantity for investigating the material damage induced by X-ray irradiation. However, the accurate calculation of the BOI is a challenge, particularly for the large deformation of materials with complex configurations. In this paper, we develop a novel two-dimensional Particle-in-Cell (PIC) code, Xablation2D, to calculate the BOIs under far-field X-ray irradiation. This significantly reduces the dependence on grid shape for numerical simulation. The reliability of this code is verified by the simulation results from the open-source codes, and the calculated BOIs are consistent with experimental and analytical results.

  • Chord length sampling correction analysis for dispersion fuel in Monte Carlo simulation

    分类: 核科学技术 >> 核科学与技术 提交时间: 2024-03-28

    摘要: Due to their excellent safety performance, dispersion fuels are widely used in advanced reactors, such as high-temperature gas-cooled reactors (HTGRs). Compared with deterministic methods, the Monte Carlo method has more advantages in the geometric modeling of stochastic media. The explicit modeling method has high computational accuracy and high computational cost. The chord length sampling (CLS) method can improve computational efficiency by sampling the chord length during neutron transport using the matrix chord length’s probability density function (PDF). This study shows that the excluded-volume effect in realistic stochastic media can introduce significant deviations into the CLS. A chord length correction approach is proposed to obtain the chord length correction factor by developing the Particle code based on equivalent transmission probability. Through numerical analysis against reference solutions from explicit modeling in the RMC code, it was demonstrated that CLS with the proposed correction method provides good accuracy for addressing the excluded-volume effect in realistic infinite stochastic media. 

  • Response characteristics of PWR primary circuit under SBLOCAs considering steam bypass discharging

    分类: 核科学技术 >> 核科学与技术 提交时间: 2024-03-21

    摘要: Small-break superposed station blackout (SBO) accidents are the basic design accidents of nuclear power plants. Under the condition of a small break in the cold leg, SBO further increases the severity of the accident, and the steam bypass discharging system (GCT) in the second circuit can play an important role in guaranteeing core safety. To explore the influence of the GCT on the thermal-hydraulic characteristics of the primary circuit, RELAP5 software was used to establish a numerical model based on a typical pressurized water reactor (PWR) nuclear power plant. Five different small breaks in the cold-leg superposed SBO were selected, and the impact of the GCT operation on the transient response characteristics of the primary and secondary circuit systems was analyzed. The results show that the GCT plays an indispensable role in core heat removal during an accident; otherwise, core safety cannot be guaranteed. The GCT was used in conjunction with the primary safety injection system during the placement process. When the break diameter was greater than a certain critical value, the core cooling rate could not be guaranteed to be less than 100 K/h; however, the core remained in a safe state.

  • 考虑气隙对矩形通道鼓泡工况流动传热行为的研究

    分类: 核科学技术 >> 核科学与技术 提交时间: 2024-03-21

    摘要: 研究针对核反应堆板状燃料组件出现的鼓泡现象,利用Fluent软件进行了数值模拟研究,并对比了裂变气体鼓泡和以往研究中固体鼓泡的区别。研究发现:气体鼓泡会导致局部温度升高,鼓泡周围热通量密度提高3倍,但燃料板整体热通量变化较小;鼓泡的形成会使鼓泡局部换热能力提高约10%,鼓泡侧热通量提高4%左右;在高流速条件下,鼓泡的存在会导致燃料板两侧流体产生较大的压力差,使得燃料板发生变形,甚至堵塞流道。研究结果为板状燃料元件设计和安全评估提供了重要参考。

  • 基于不同评价核数据库的空间堆临界基准检验研究

    分类: 核科学技术 >> 核科学与技术 提交时间: 2024-03-15

    摘要: 为提高空间堆中子学模拟的可靠性,基于国际临界安全手册中关于空间堆的临界基准实验(HMF005基准实验),采用蒙特卡罗程序对HMF005基准实验中堆芯排布进行建模,结合不同评价核数据库,计算6种堆芯排布下的keff计算值与实验值的偏差,并对计算值与实验值的比值的平均值、标准偏差、χ2和均方根误差等进行深入分析。研究发现,ENDF/B-VII.1、CENDL-3.2、ENDF/B-VIII.0和JEFF-3.3四种评价核数据库计算堆芯keff结果与实验值偏差处于三倍不确定度之内,其中ENDF/B-Ⅶ.1计算结果最接近实验值,CENDL-3.2与实验偏差稍大。CENDL-3.2库计算结果与实验值偏差稍大主要是由于评价库中的钼和铍核素导致,钼的同位素中92Mo的影响最大。同时还进行敏感性分析,92Mo和9Be的总反应敏感性系数主要跟弹性散射敏感性系数相关,CENDL-3.2和ENDF/B-Ⅶ.1中9Be的辐射俘获敏感性差异较大,两者偏差可达34.9%。

  • 用于高计数率TPC探测器的增益自适应前放芯片设计

    分类: 核科学技术 >> 核科学与技术 提交时间: 2024-03-13

    摘要: 针对强流下时间投影室TPC(Time Projection Chamber)探测器高计数率,大动态范围、低功耗的读出需求,基于180nm CMOS工艺设计了一种自动调节增益的前放芯片。该芯片由电荷灵敏前放CSA(Charge Sensitive Amplifier)、Class AB输出缓冲级、增益控制模块、触发控制模块构成。通过片内逻辑信号控制多个开关的切换,使芯片的转换增益自适应输入电荷量;并通过开关泄放,使芯片工作于1MHz计数率。经过仿真,在输入信号范围为2.2 fC-16.5 pC时,积分非线性好于0.4%。该芯片已经提交foundry流片。

  • Bunch-length measurement at a bunch-by-bunch rate based on time–frequency-domain joint analysis techniques and its application

    分类: 核科学技术 >> 核科学与技术 提交时间: 2024-03-12

    摘要: This paper presents a new technique for measuring the bunch length of a high-energy electron beam at a bunch-by-bunch rate in storage rings. This technique uses the time–frequency-domain joint analysis of the bunch signal to obtain bunch-by-bunch and turn-by-turn longitudinal parameters, such as bunch length and synchronous phase. The bunch signal is obtained using a button electrode with a bandwidth of several gigahertz. The data acquisition device was a high-speed digital oscilloscope with a sampling rate of more than 10 GS/s, and the single-shot sampling data buffer covered thousands of turns. The bunch length and synchronous phase information were extracted via offline calculations using Python scripts. The calibration coefficient of the system was determined using a commercial streak camera. Moreover, this technique was tested on two different storage rings and successfully captured various longitudinal transient processes during the harmonic cavity debugging process at the Shanghai Synchrotron Radiation Facility (SSRF), and longitudinal instabilities were observed during the single bunch accumulation process at Hefei Light Source (HLS). For Gaussian-distribution bunches, the uncertainty of the bunch phase obtained using this technique was better than 0.2 ps, and the bunch length uncertainty was better than 1 ps. The dynamic range exceeded 10 ms. This technology is a powerful and versatile beam diagnostic tool that can be conveniently deployed in high-energy electron storage rings.

  • Ultrahigh spatiotemporal Resolution Beam Signal Reconstruction with bunch phase compensation

    分类: 核科学技术 >> 核科学与技术 提交时间: 2024-03-08

    摘要: Various electromagnetic signals are excited by the beam in the acceleration and beam-diagnostic elements of a particle accelerator. It is important to obtain time-domain waveforms of these signals with high temporal resolution for research, such as the study of beam-cavity interactions and bunch-by-bunch parameter measure#2;ments. Therefore, a signal reconstruction algorithm with ultrahigh spatiotemporal resolution and bunch phase compensation based on equivalent sampling is proposed in this paper. Compared with traditional equivalent sampling, the use of phase compensation and setting the bunch signal zero-crossing point as the time reference can construct a more accurate reconstructed signal. The basic principles of the method, simulation, and experi#2;mental comparison are also introduced. Based on the beam test platform of the Shanghai Synchrotron Radiation Facility (SSRF) and the method of experimental verification, the factors that affect the reconstructed signal qual#2;ity are analyzed and discussed, including the depth of the sampled data, quantization noise of analog-to-digital converter (ADC), beam transverse oscillation, and longitudinal oscillation. The results of the beam experiments show that under the user operation conditions of the Shanghai Synchrotron Radiation Facility (SSRF), a beam excitation signal with an amplitude uncertainty of 2% can be reconstructed.

  • CAT-1偶极场超导磁体的悬浮控制与仿真

    分类: 核科学技术 >> 核科学与技术 提交时间: 2024-03-03

    摘要: 针对天环一号(CAT-1: China Astro-Torus 1)偶极场等离子体物理实验要求,装置要求中心漂浮超导线圈在无冷却和无电源条件下稳定悬浮至少5hr,设计了超导托举线圈与中心漂浮线圈耦合系统的悬浮控制系统。为确保1200 kg、5 MA悬浮磁体稳定悬浮,完成了控制系统的Simulink模型建立和仿真,基于 Routh-Hurwitz稳定判据,研究了PID控制策略对稳定控制影响,确定了稳定控制参数选取的范围:当驱动托举线圈的电源响应频率应大于9 Hz,输出电流的误差小于0.1%时,理想条件下PD控制系统最有控制效果为延迟时间为0.0463 s、上升时间为0.1545 s、峰值时间为0.6283 s、调节时间0.0848 s、超调量δ=1.6,稳态误差err小于0.05 mm,为电源相应频率大于9 Hz,输出误差小于0.05%。结果表明:基于PID能够在较短的时间内将悬浮超导环在预设位置,且采用合适的启动方式情况下,可极大的降低电路的负载,并为悬浮超导悬浮偶极场装置的技术可行性提供有力支撑。

  • Corrosion behavior of pure metals (Ni and Ti) and alloys (316H SS and GH3535) in liquid GaInSn

    分类: 核科学技术 >> 核科学与技术 提交时间: 2024-02-19

    摘要: In this study, the interactions between a Ga-based liquid metal,GaInSn, and several metal materials, including pure metals (Ni and Ti) and alloys (316H stainless steel (SS) and GH3535), at 650 °C were investigated. The aim was to evaluate the corrosion performance and select a suitable candidate material for use as a molten salt manometer diaphragm in thermal energy storage systems. The results indicated that the alloys (316H SS and GH3535) exhibited less corrosion than pure metals (Ni and Ti) in liquid GaInSn. Ga-rich binary intermetallic compounds were found to form on the surfaces of all the tested metal materials exposed to liquid GaInSn, as a result of the decomposition of liquid GaInSn and its reaction with the constituent elements of the metal materials. The corrosion mechanism for all the tested materials exposed to liquid GaInSn was also investigated and proposed, which may aid in selecting the optimal candidate material when liquid GaInSn is used as the pressure-sensing medium

  • An efficient parallel algorithm of variational nodal method\\for heterogenous neutron transport problems

    分类: 核科学技术 >> 核科学与技术 提交时间: 2024-02-13

    摘要: The heterogeneous variational nodal method (HVNM) has emerged as a potential approach for solving high-fidelity neutron transport problems. However, achieving accurate results with HVNM in large-scale problems using high-fidelity models has been challenging due to the prohibitive computational costs. This paper presents an efficient parallel algorithm tailored for HVNM based on the Message Passing Interface standard. The algorithm evenly distributes the response matrix sets among processors during the matrix formation process, thus enabling independent construction without communication. Once the formation tasks are completed, a collective operation merges and shares the matrix sets among the processors. For the solution process, the problem domain is decomposed into subdomains assigned to specific processors, and the red-black Gauss-Seidel iteration is employed within each subdomain to solve the response matrix equation. Point-to-point communication is conducted between adjacent subdomains to exchange data along the boundaries. The accuracy and efficiency of the parallel algorithm are verified using the KAIST and JRR-3 test cases. Numerical results obtained with multiple processors agree well with those obtained from Monte Carlo calculations. The parallelization of HVNM results in eigenvalue errors of 31 pcm/-90 pcm and fission rate RMS errors of 1.22%/0.66%, respectively, for the 3D KAIST problem and the 3D JRR-3 problem. In addition, the parallel algorithm significantly reduces computation time, with an efficiency of 68.51% using 36 processors in the KAIST problem and 77.14% using 144 processors in the JRR-3 problem.

  • CAFE-2同步定时触发系统设计

    分类: 核科学技术 >> 核科学与技术 提交时间: 2024-02-04

    摘要: CAFE-2是中国科学院近代物理研究所于2021年建造、用于开展超重新核素合成、超重元素化学性质、超重核结构和性质等方面的研究的超导直线加速器。同步定时触发系统是CAFE-2的重要子系统,在CAFE-2的运行中起着关键性的作用。为了满足CAFE-2在加速器调试及终端运行两种运行模式下不同运行时序及同步触发的需求,CAFE-2主同步定时系统采用了经典的基于事件的定时方案,同时通过耦合电路及联锁逻辑设计,在终端运行模式下将旋转靶调制的同步脉冲信号与主定时CW(Continuous-wave)模式下的触发信号进行耦合,解决了CAFE-2在终端运行模式下触发信号必须与旋转靶脉冲信号同步的难题。本文介绍了CAFE-2同步定时触发系统的结构,并阐述了CAFE-2在不同运行模式下同步定时触发系统的工作原理与方案。

  • 大功率晶闸管在聚变环境中受中子辐照影响研究

    分类: 核科学技术 >> 核科学与技术 提交时间: 2024-01-26

    摘要: 大功率晶闸管器件以其良好的经济性和适用性,被广泛应用于大型聚变装置的供电系统中。氘-氚(D-T)聚变反应产生的高剂量中子长时间照射晶闸管,将导致晶闸管的电学特性发生变化,最终造成不可逆的损伤。本文以聚变装置超导磁体失超保护系统(QPS)中换流回路的晶闸管开关为研究对象。建立了辐照晶闸管内部物理结构与外部电气参数之间的关系。然后,进行了一系列有针对性的晶闸管物理模拟和中子辐照实验,验证了理论分析的正确性。此外,通过精确仿真研究了辐照晶闸管电气特性变化对QPS的影响,为QPS的维护和改造提供了有价值的指导。

  • 基于速度-动能法的中子诱发裂变谱仪物理设计

    分类: 核科学技术 >> 核科学与技术 提交时间: 2024-01-22

    摘要: 随着第四代核反应堆和新型核能利用系统的快速发展,以及超重核熔合机制和天体核物理中的快中子俘获反应等领域的研究进展,使得中子诱发重核裂变研究及裂变数据测量成为国际上核物理研究的新热点。本工作完成了基于速度-动能法的中子诱发裂变谱仪的物理设计。设计了MCP二次电子时间探测器,二次电子飞行时间展宽控制在50ps,TOF长度设计为70cm。选择屏栅电离室为能量探测器,工作气体选择为异丁烷,最佳约化场强为6V/(cmtorr),气压为37.5Torr,采用COMSOL、Geant4、Garfield++等程序耦合计算了裂变碎片在屏栅电离室中的能量响应,谱仪系统的能量分辨率为0.36~0.55%。综合分析,本工作设计的基于速度-动能法的中子诱发裂变谱仪,轻裂变碎片能量分辨率小于0.8%,重裂变碎片小于0.6%,中子诱发重核裂变的质量分辨小于1amu。此外,基于设计的裂变谱仪物理结构,本工作模拟计算了14MeV中子诱发238U裂变产额质量分布与电荷分布数据,与ENDF-VII基本一致,为中子诱发典型锕系重核裂变物理实验测量准备了条件。

  • Design of Weak Current Measurement System and Research on Temperature Impact

    分类: 核科学技术 >> 核科学与技术 提交时间: 2024-01-10

    摘要: To measure the weak currents generated by the neutron ionization chamber, a dedicated weak current measurement system was designed. This system incorporates a second-order low-pass filter circuit and the Kalman filtering algorithm to effectively filter out noise and minimize interference on the measurement results. Testing conducted under normal temperature conditions has demonstrated the system's high precision performance. However, it was observed that temperature variations can affect the measurement performance. To address this issue, data was collected across temperatures ranging from -20 to 70C, and a temperature correction model was established through linear regression fitting. The feasibility of the temperature correction model was confirmed at temperatures of -5 and 40C, where relative errors remained below 0.1% after applying the temperature correction. The research indicate that the designed measurement system exhibits excellent temperature adaptability and high precision, making it particularly suitable for measuring weak currents.

  • Artificial neural network-based method for discriminating Compton scattering events in high-purity germanium γ-ray spectrometer

    分类: 物理学 >> 核物理学 分类: 核科学技术 >> 核科学与技术 分类: 核科学技术 >> 核探测技术与核电子学 提交时间: 2024-01-08

    摘要: To detect radioactive substances with low activity levels, an anticoincidence detector and a high-purity germanium (HPGe) detector are typically used simultaneously to suppress Compton scattering background, thereby resulting in an extremely low detection limit and improving the measurement accuracy. However, the complex and expensive hardware required does not facilitate the application or promotion of this method. Thus, a method is proposed in this study to discriminate the digital waveform of pulse signals output using an HPGe detector, whereby Compton scattering background is suppressed and a low minimum detectable activity (MDA) is achieved without using an expensive and complex anticoincidence detector and device. The electric-field-strength and energy-deposition distributions of the detector are simulated to determine the relationship between pulse shape and energy-deposition location, as well as the characteristics of energy-deposition distributions for full- and partial-energy deposition events. This relationship is used to develop a pulse-shape-discrimination algorithm based on an artificial neural network for pulse-feature identification. To accurately determine the relationship between the deposited energy of gamma rays in the detector and the deposition location, we extract four shape parameters from the pulse signals output by the detector. Machine learning is used to input the four shape parameters into the detector. Subsequently, the pulse signals are identified and classified to discriminate between partial- and full-energy deposition events. Some partial-energy deposition events are removed to suppress Compton scattering. The proposed method effectively decreases the MDA of an HPGe -energy dispersive spectrometer. Test results show that the Compton suppression factors for energy spectra obtained from measurements on 152Eu, 137Cs, and 60Co radioactive sources are 1.13 (344 keV), 1.11 (662 keV), and 1.08 (1332 keV), respectively, and that the corresponding MDAs are 1.4%, 5.3%, and 21.6% lower, respectively