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.
分类: 核科学技术 >> 粒子加速器 提交时间: 2024-03-25
摘要: 光核反应和紧凑型中子源是生产医用同位素的新兴工具,东华理工大学(ECUT)正在建设一种电子加速器驱动的光中子源(ECANS),用于医用同位素生产研究。本文在分析W- 100Mo光中子源的中子产额及99Mo产量的基础上,建立了中子能量调节层和中子反射层组成的放射性同位素产生模型,对不同天然氧化物材料(MoO3、Lu2O3、Y2O3)进行了放射性同位素的产生模拟及伴生产物分析,探讨了光核反应中子源生产医用同位素的可行性。研究结果显示,在高富集100Mo靶材中99Mo同位素的产量为54.1 Ci/day,在氧化物靶材中99Mo的产量为17.4 Ci/day、177Lu的产量为18.2 Ci/day以及90Y的产量为57.0 Ci/day。此外分析了天然氧化物在辐照条件下放射性杂质的含量,为后续分离纯化提供数据参考。
分类: 核科学技术 >> 核材料与工艺技术 提交时间: 2024-03-25
摘要: 氧化石墨烯(Graphene Oxide,GO)掺杂改性二氧化铀(UO2)芯块是高性能核燃料研究的重点方向之一。为实现GO在UO2芯块中的均匀分布及掺杂量控制,利用固-液混合法和ADU(Ammonium diuranate)共沉淀法制备了不同GO掺杂量的UO2粉末,研究了制粉方法及GO掺杂量对GO在UO2中混合均匀性的影响。采用放电等离子烧结制备了不同GO掺杂量的UO2-GO芯块,探索了不同烧结参数的影响,并对燃料芯块的性能进行测试。结果表明,固-液混合法制备的GO掺杂UO2粉末混合均匀度更好;放电等离子烧结得到的UO2-GO芯块密度最高可达97.6% T.D.;GO掺杂量为1.5 wt.%的芯块在1000 ℃下的热导率较常规UO2芯块提高了85.9%;制备的UO2-GO芯块晶粒尺寸较为均匀,GO均匀分布在晶界处并形成了桥联导热网络,有效提升了掺杂芯块的热导率。
分类: 核科学技术 >> 粒子加速器 提交时间: 2024-03-24
摘要: X波段高梯度加速结构是能有效减小常温直线型加速器体积的核心部件。清华大学加速器实验室成功研制了0.65 m的X波段高梯度行波等阻抗加速结构。经过一系列精密的加工流程和调谐过程,加速结构的微波测试达到了预期的结果,进而在清华大学X波段高功率微波平台上进行高功率测试。测试过程中,整管的平均加速梯度达到了80 MV/m,首腔的平均加速梯度超过110 MV/m,达到了国际的前列水平。该结构的研制还将为清华大学承建的紧凑型准单能伽马源(VIGAS)项目提供重要的技术支撑。
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.
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。
分类: 核科学技术 >> 核材料与工艺技术 提交时间: 2024-03-20
摘要: 在第四代反应堆中,核石墨作为慢化体和反射体材料服役于高温和高通量的快中子辐照环境中。快中子辐照会在核石墨中产生大量的弗伦克尔缺陷对。这些缺陷经过湮灭、扩散、最终形成更大的缺陷团簇,从而改变核石墨的微观结构,进而改变核石墨的宏观性能。因此,研究核石墨在高温辐照条件下的缺陷演化行为和机理对提高反应堆安全性具有重要意义。本研究采用30 MeV的107Ag5+离子在420 ℃下辐照IG-110核石墨来模拟核石墨在快中子辐照过程中的缺陷演化行为。通过微区拉曼光谱对IG-110核石墨截面结构进行表征,并对比IG-110核石墨不同深度处的拉曼光谱特征参数和辐照损伤剂量之间的关系,研究IG-110微观结构随辐照损伤剂量(DPA, Displacements Per Atom)的演化行为。研究结果表明,随着注量的增加,核石墨拉曼光谱的特征参数D峰高度与G峰高度比值(ID/IG)、G峰半高宽(FWHM(G), Full Width at Half Maximum of the G peak)以及G峰的偏移量都显著增加。与58Ni5+辐照样品相比,相同辐照损伤剂量下, 107Ag5+辐照的石墨拉曼光谱的ID/IG和FWHM(G)更大。相同的FWHM(G)下,107Ag5+辐照的石墨拉曼光谱的ID/IG比58Ni5+辐照样品大。这些结果说明更重的重离子辐照会在核石墨中引起更高速率的缺陷积累,从而更快地导致石墨晶粒尺寸变小,并促进纳米晶化进程。
分类: 核科学技术 >> 核探测技术与核电子学 提交时间: 2024-03-20
摘要: 气体探测器中工作气体的平均电离能、法诺因子及漂移速度等性质对于探测器的前期模拟及参数设计乃至径迹重建有着重要影响。SeF6 作为国内无中微子双贝塔衰变实验中的目标工作气体,相关参数未知需要探究。为研究该气体相关参数设计了一套测量方案, 并采用 Ar/CH4=90/10(P10) 工作气体对该实验方案的测量精度和可靠性进行了检验。实验中通过屏栅电离室测量 𝛼 源得出 P10 平均电离能为 27.10±0.04 eV、当能量分辨率达到 0.91% 时,刻度电子学后扣除噪声得到法诺因子为 0.175±0.001。同时采用266 nm 激光和时间投影室完成漂移速度的测量,其结果与 Garifield++ 模拟结果吻合。实验结果表明该测量方案可行,测量结果可靠性高。为后续开展 SeF6 性质的研究工作做好了准备。
分类: 核科学技术 >> 粒子加速器 提交时间: 2024-03-19
摘要: 超导同步回旋加速器具有超小型结构,造价更低,更适合应用于医院环境使用的质子治疗系统。相比于现在的质子治疗系统,应用了超导同步回旋加速器的质子治疗系统单次进行肿瘤治疗的费用更低,具有巨大的应用前景,因此取得许多加速器研发机构和企业的高度重视。再生引出系统是超导同步回旋加速器的关键系统,也是超导同步回旋加速中设计的关键和难点。本文针对一台质子治疗用230MeV质子超导同步回旋加速器开展了再生引出系统设计。由于再生引出系统与主磁场紧密相关,文章第一部分先开展了主磁铁的设计,并给出相关的动力学计算结果。现有的回旋加速器设计程序并没有针对同步回旋加速器再生引出系统的设计功能,故本文开发了能够进行再生引出系统设计的程序。设计结果显示230 MeV质子超导同步回旋加速器再生引出系统的设计满足引出要求,可以为超导同步回旋加速器其他系统的设计及工程建造提供参考。
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%。
分类: 核科学技术 >> 核探测技术与核电子学 提交时间: 2024-03-15
摘要: 在软X射线能谱探测中,采用硅漂移探测器(Silicon Drift Detector,SDD)与复位型电荷灵敏前置放大器集成的一体化探测设备,其输出信号为包含射线能谱信息的阶梯型锯齿波。文章针对该设备产生的阶梯型锯齿波信号无法直接精确提取幅度信息的问题,提出了一种用模拟电路对该信号进行整形放大处理的方案,并通过Cadence软件仿真的方法,探究了此方案的可行性以及在该方案下影响能谱能量分辨率的因素。文章还通过对比不同噪声幅度输入时电路的输出信号,最终得到在相应的能量分辨率指标要求下前放输出信号噪声指标的最低要求。
分类: 核科学技术 >> 核材料与工艺技术 提交时间: 2024-03-13
摘要: Cs and I can migrate through the fuel-cladding interface and accelerate the cladding corrosion process induced by the Fuel Cladding Chemical Interaction. Cr coating is an important candidate in mitigating this chemical interaction. First-principles calculations were employed to investigate the diffusion behaviors of Cs and I in Cr bulk and Cr grain boundary, aiming to reveal the microscopic mechanisms for mitigating the interaction at fuel-cladding interface. The interactions between these two fission products and Cr coating were systematically studied, and the temperature-dependent diffusion coeffcients of Cs and I in Cr were obtained using Bocquet’s oversized solute atoms model and Le Claire’s nine-frequency model, respectively. The results show that the migration barriers of Cs and I are significantly lower compared to that of Cr, and the diffusion coeffcients of Cs and I are both more than 3 orders of magnitude larger than Cr self-diffusion coeffcient within the temperature range of Generation IV fast reactors (below 1000 K), which shows the strong penetration ability of Cs and I. Meanwhile, Cs and I are more likely to diffuse along the grain boundary because of the generally low migration barriers, indicating that grain boundary serves as a fast diffusion channel for Cs and I.
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。
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.
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.
分类: 核科学技术 >> 核探测技术与核电子学 提交时间: 2024-03-07
摘要: The High Energy Cosmic-Radiation Detection (HERD) facility is planned to launch in 2027 and scheduled to be installed on the China Space Station. It serves as a dark matter particle detector, a cosmic ray instrument, and an observatory for high-energy gamma rays. A transition radiation detector placed on one of its lateral sides serves dual purpose, (i) calibrating HERD’s electromagnetic calorimeter in the TeV energy range, and (ii) serving as an independent detector for high-energy gamma rays. In this paper, the prototype readout electronics design of the transition radiation detector is demonstrated, which aims to accurately measure the charge of the anodes using the SAMPA application specific integrated circuit chip. The electronic performance of the prototype system is evaluated in terms of noise, linearity, and resolution. Through the presented design, each electronic channel can achieve a dynamic range of 0-100 fC, the RMS noise level not exceeding 0.15 fC, and the integral nonlinearity was less than 0.2%. To further verify the readout electronic performance, a joint test with the detector was carried out, and the results show that the prototype system can satisfy the requirements of the detector’s scientific goals.
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。
分类: 核科学技术 >> 核科学技术其他学科 分类: 物理学 >> 核物理学 提交时间: 2024-02-28
摘要: Ferritic/martensitic (F/M) steels have been widely used as structural material for thermal and nuclear power plants. However, it is susceptible to intergranular damage in service conditions, which is expected to be critical issues. In order to improve the intergranular damage resistance of F/M steel, thermomechanical process (TMP) was employed to achieve a grain boundary engineering (GBE) microstructure in a kind of F/M steel P92 in this study. TMP, including cold rolling to 6%, 9%, and 12% thickness reduction, respectively, followed by austenization at 1323 K for 40 min plus tempering at 1053 K for 45 min, were applied on as-received (AR) P92 steel. Both prior austenite grain (PAG) size, prior austenite grain boundary character distribution (GBCD), and the connectivity of prior austenite grain boundaries (PAGBs) were investigated. Compared with AR specimen, the PAG size does not change significantly. The fraction of coincident site lattice boundaries (CSLBs, 3 ≤ Σ ≤ 29) and Σ3n boundaries along PAGBs decreases with increasing reduction ratio due to the recrystallization fraction increases with increasing reduction ratio. The PAGBs connectivity of the 6%-deformed specimen deteriorates compared with that of AR specimen slightly. Moreover, the potentiodynamic polarization studies revealed that the intergranular damage resistance of studied steel could be improved by enhancing the fraction of CSLBs along PAGBs, indicating that TMP, involving low deformation, could enhance the intergranular damage resistance.
分类: 物理学 >> 核物理学 分类: 核科学技术 >> 核探测技术与核电子学 提交时间: 2024-02-27
摘要: 正在建设中的强流重离子加速器装置 HIAF 配备了一条先进的放射性束流线 HFRS,建成后将为中国 高能放射性核束物理研究提供新的机遇。HFRS 的特点是流强极高 (初级束流强度 1 × 1011 ppp),这对用于粒 子鉴别的能损探测器提出了非常高的计数率要求。传统的能损探测器对信号处理一般依次采用电荷灵敏前放、 主放、ADC 的技术路线。该方案存在电子学响应速度较慢、灵活性较差、难以处理高计数率下信号堆积严重 等问题。我们对此提出一种新的适用于高计数率的能损探测器方案:以耐辐照的多次取样电离室为能损探测 器,优化结构和读出方式提高探测器响应速度,使用快电荷灵敏前放对能损探测器信号初步放大后、直接用 波形数字化仪采集波形再进行后续数字算法处理。并利用放射源和束流对该方案进行了验证测试。利用 3 组 分 𝛼 源测试时,对采集的波形使用数字成形算法处理,能量分辨率(FWHM)可达 1.31%。在 RIBLL2 提供 300 MeV/u 的 56Fe 束流测试中,采用时间常数 𝜏f = 2 𝜇𝑠 的快电荷灵敏前放在计数率接近 1 MHz 时仍未发生明显堆积。
分类: 物理学 >> 核物理学 分类: 核科学技术 >> 核聚变工程技术 提交时间: 2024-02-27
摘要: The helium bubbles induced by 14 MeV neutron irradiation can cause intergranular fractures in reduced activation ferritic martensitic (RAFM) steel, which is a candidate structural material for fusion reactors. In order to elucidate the susceptibility of different grain boundaries (GBs) to helium-induced embrittlement, the tensile fracture processes of 10 types of GBs with and without helium bubbles in body-centered cubic (bcc) iron at the relevant service temperature of 600 K were investigated via molecular dynamics methods. The results indicate that in the absence of helium bubbles, the GBs studied here can be classified into two distinct categories: brittle GBs and ductile GBs. The atomic scale analysis shows that the plastic deformation of ductile GB at high temperatures originates from complex plastic deformation mechanisms, including the Bain/Burgers path phase transition and deformation twinning, in which the Bain path phase transition is the most dominant plastic deformation mechanism. However, the presence of helium bubbles severely inhibits the plastic deformation channels of the GBs, resulting in a significant decrease in elongation at fractures. For bubble-decorated GBs, the ultimate tensile strength increases with the increase of the misorientation angle. Interestingly, the coherent twin boundary Ʃ3{112} was found to maintain relatively high fracture strength and maximum failure strain under the influence of helium bubbles.