临界装置绝对裂变率测量

临界装置是在低功率下运行的能够维持可控自持链式裂变反应的装置，一般运行的热功率在1kW以下，与动力堆相对应，一般称为零功率装置。在临界装置上进行的各项研究中，一个重要的参数就是裂变反应率(简称裂变率)，它是其它参数测量的基准，如在脉冲式的反应堆中，还是脉冲裂变总数的测量基准，是脉冲堆的一个主要指标。     

基于脉冲中子源法的CiADS反应性测量蒙卡模拟分析

脉冲中子源法(PNS)是加速器驱动次临界系统反应性测量的一种重要技术.利用蒙卡软件建立CiADS次临界反应堆模型,模拟注入脉冲质子束的过程,获得的中子通量的时间演化谱.采用Python语言编程实现脉冲叠加过程,给出稳定缓发中子本底,实现脉冲中子源法的次临界反应堆的反应性测量模拟,给出脉冲周期注入下堆芯不同位置处的中子变...     

散射中子对超瞬发临界系统动态行为的影响北大核心CSCD

在点反应堆理论的基础上,建立了研究散射中子影响超瞬发临界系统动态行为的模拟计算方法,利用CFBR-Ⅱ堆的脉冲实验验证了该方法的正确性。通过分析计算表明,在超瞬发临界状态,散射中子的影响包括增加反应性、使脉冲波形后沿展宽和增加脉冲裂变产额。建立的模拟计算方法为预测脉冲堆外各种物体产生的散射中子的动力学效应提供了途径,对提高脉冲堆的核安全有应用价值。     

铀氢锆脉冲反应堆

 1989年4月6日,我国核工业第一研究设计院,在铀氢锆脉冲反应堆零功率装置上,成功地实现了首次临界.标志我国在研制开发这一新型反应堆方面,迈出了重要的一步.什么是脉冲反应堆脉冲反应堆,是一种具有稳态和脉冲运行特殊功能的核反应堆.核反应堆,是中子使原子核发生链式反应,并伴随放出大量粒子和巨大能量的可控核反应器.     

有温度反馈阶跃引入负反应性瞬变的解

考虑有温度反馈反应堆阶跃引入负反应性过程的变化规律,对点堆中子动力学方程的解进行研究,给出不同的分析模型,分析发现,（1）用于瞬发超临界的分析模型及其结果不能用于引入大的负反应性过程的分析.（2）在相同的初始功率时,先驱核瞬跳近似模型的结果要优于目前比较普遍的中子瞬跳近似模型的结果.（3）无论初始功率与引入负阶跃反应性的大小,温度瞬跳近似模型的结果总是优于先驱核瞬跳近似与中子瞬跳近似模型的结果.故而温度瞬跳近似模型是目前最为准确的解析模型. 关键词： 中子动力学 温度反馈 反应性 点堆     

“强光”1号Z-Pinch实验一维空间分布X-Ray辐射特性

测量零功率堆中子衰变常数α（负λ参数）通常用罗西一磁或随机脉冲源法等。但这些测量方法费时较长，为适应实验需要进行了瞬态测量方法研究。瞬态法负λ测量的特点：需要一个高强度、窄脉冲外中子源（比如说DPF中子源）；测点处有很强的直照中子和散射本底，比被测信号高3个多量级；进行负λ测量时必须对探测器进行屏蔽，为减少屏蔽体体积开展了门控PMT负λ测量技术研究。     

高温气冷堆堆芯中子时空动力学模拟计算

研究开发三维圆柱几何堆芯多群中子时空动力学改进准静态方法模拟计算程序.对给定的模块式高温气冷堆模型进行模拟计算.初始状态下,计算结果与中子扩散程序CITATION吻合很好.动态情况下,模拟堆芯反应性、堆内各能群中子平均注量率和堆芯相对功率等物理量随时间变化,计算结果与理论分析一致.     

基于FLUENT的核热耦合程序反应性反馈参数敏感性

将计算流体力学模型与中子动力学模型耦合来进行反应堆瞬态安全分析的方法,由于可以开展复杂几何结构的三维流动传热分析,因此受到很大的关注。基于FLUENT用户自定义功能（UDF）开发了一套可用于池式铅堆瞬态安全分析的核热耦合程序,程序耦合了临界/次临界点堆中子动力学模型和燃料棒模型。由于反应堆处于不同寿期时,随着燃料燃耗、可燃毒物积累等因素导致反应性反馈系数有较大变化,因此使用开发的核热耦合程序对中国科学技术大学提出的小型自然循环铅冷快堆进行不同关键反馈系数下无保护的瞬态超功率事故安全分析。调整点堆模块考虑到的四个反应性反馈系数,可以发现燃料多普勒系数对堆安全的影响最大,同时定量的分析结果表明超功率事故引入时间长短对事故演化有重要影响。     

激光脉冲参数对冲击点火的影响

针对激光脉冲参数对冲击点火的影响进行理论分析和数值模拟.首先从冲击波的产生和碰撞过程出发,理论分析冲击脉冲峰值功率、脉宽和上升沿时间对点火的影响;然后通过数值模拟,以点火时间窗口作为评价标准,验证理论分析结果.研究表明:冲击脉冲峰值功率是点火成败的关键因素之一,脉冲宽度则需达到百皮秒以提供足够的点火能量,上升沿时间在小于600 ps的情况下不会对点火造成明显影响. 关键词： 冲击点火 激光冲击脉冲 点火时间窗口     

有温度反馈阶跃引入负反应性瞬变的解

考虑有温度反馈反应堆阶跃引入负反应性过程的变化规律,对点堆中子动力学方程的解进行研究,给出不同的分析模型,分析发现,（1）用于瞬发超临界的分析模型及其结果不能用于引入大的负反应性过程的分析.（2）在相同的初始功率时,先驱核瞬跳近似模型的结果要优于目前比较普遍的中子瞬跳近似模型的结果.（3）无论初始功率与引入负阶跃反应性的大小,温度瞬跳近似模型的结果总是优于先驱核瞬跳近似与中子瞬跳近似模型的结果.故而温度瞬跳近似模型是目前最为准确的解析模型.     

启明星Ⅱ次临界非稳态热中子注量率测量

中子注量率及分布是反应堆的重要参数,本工作通过核数守恒在非稳态情况下的推导和求解,从理论上论证了次临界反应堆非稳态情况下中子注量率测量的可行性。将活化法和固体径迹法有机结合,利用固体径迹探测器标定活化片的测量数据,测量了启明星Ⅱ零功率装置的He-3管实验孔道内及反应堆外壁的中子注量率的分布,并与模拟计算结果进行了比较,利用MCNPX程序得到的模拟计算结果与实验结果的趋势一致,证明了该测量方法可以测量低通量的中子注量率,可实现反应堆不同时刻、不同位置的中子注量率测量,为CiADS技术的研发提供了实验数据与技术支撑。Neutron flux measurements were carried out at VENUS-Ⅱ lead-based zero power reactor by neutron activation method combined with solid-state nuclear track detectors (SSNTD). This experimental method was proposed based on the principle of nuclear number conservation when a foil was irradiated in an unsteady-state neutron field. By this method, thermal neutron flux distributions inside the He-3 duct were measured when VENUS-Ⅱ was operated under unsteady-state. The neutron flux distributions were also calculated with MCNPX code and were consistent with the experimental data. In addition, the neutron fluxes in the outer layer of VENUSⅡ were measured under steady-state. These results would benefit the further study of experimental methods for neutron flux measurement and provide important support for the design of CiADS.     

加速器驱动次临界系统中堆外中子注量率监测方法（英文）

在加速器驱动的次临界（ADS）系统中,次临界反应堆的功率控制是通过控制束流强度来实现。监测堆外中子注量率,不仅提供了反应堆功率指示,也为反应堆保护系统在启动和运行阶段提供了重要的监测信息,因此,堆外中子注量率的监测在ADS系统的控制与保护中起着非常重要的作用。采用3套裂变室和3套非补偿电离室来监测ADS堆外中子注量率。由于裂变室有脉冲、电流和均方电压3种操作模式,1套裂变室可以监测源量程、中间量程和功率量程等宽范围的反应堆功率。所以,使用的监测方法有3个优点,即:增加了监测通道的冗余度,提高了保护系统的可靠性,以及能提供更多的轴向功率分布信息。由于这些中子探测器对中子能谱很敏感,提出了一种有效的校准方法,即先用一个标准的中子源校准这些中子探测器,然后再将中子注量率除以一个修正因素。基于Geant4仿真结果显示,所提取的裂变室和非补偿电离室的修正因素分别为5和42。In an accelerator driven sub-critical (ADS) system, power control in sub-critical reactor is achieved through the control of the beam current. Excore neutron flux monitoring in an ADS system, not only provides indication of reactor power, but also provides important inputs to reactor protection system during startup and power operation, and thus plays a very important role in the control and protection of ADS system. This paper presents the excore neutron flux monitoring method which uses three fission chambers (FCs) and three uncompensated ion chambers (UICs). With three operation modes, pulse mode, current mode, and mean square voltage mode, an FC can monitor reactor power over a wide range from the source range to the intermediate and power ranges. The proposed monitoring method increases the redundancy of independent monitoring channels, improves the reliability of the protection system, and provides more information on axial power distribution. Since these neutron detectors are sensitive to the neutron energy spectrum, we propose an effective calibration method to provide the exact value of neutron flux, i.e., these neutron detectors are calibrated with a standardized neutron source, and then, a correction factor is added in the calibration by comparing the neutron energy spectrum of the neutron source with that in ADS system. Based on Geant4 simulation, the correction factors of 5 and 42 are extracted for FCs and UICs, respectively.     

Z箍缩聚变裂变混合堆包层中子学分析

作为一种有竞争力的能源系统,Z箍缩聚变裂变混合堆(Z-FFR)正在开展概念研究,包层研究正是其中重要的一部分。建立了Z-FFR包层设计模型,分析了包层影响因素、中子平衡、通量与功率密度、燃耗等方面,表明该包层设计在50年内能量放大因子、氚增殖比和燃料增殖比的平均值分别为14.91,1.294和5.140,满足设计要求。针对聚变源的脉冲特性进行了包层的瞬态中子学分析,发现燃料区中子脉冲可分为聚变中子、瞬发裂变中子和缓发裂变中子脉冲三个部分,绝大部分热量约在0.01s内沉积。结果较完整地给出了Z-FFR包层的中子学参数,为概念研究提供了基础。     

Pulse-Width Jitter Measurement for Laser Diode Pulses

Theoretical analysis and experimental measurement of pulse-width fitter of diode laser pulses are presented. The expression of pulse power spectra with all amplitude jitter, timing jitter and pulse-width jitter is deduced. The power spectra with and without pulse-width fitter are that the pulse-width jitter will contribute considerably numerically simulated. The simulation results indicate noise to the pulse power spectrum while the product of pulse width and angular frequency is larger than 1. The experimental measurement of pulse-width fitter of a gain-switched Fabry-Perot laser diode with 2.4 GHz repetition rate is also reported. In comparison of the noise power spectra of the first, fourth and seventh harmonics of the pulse repetition rate, 2.3ps pulse-width jitter is obtained.     

On Measurement of Subcriticality of Reactors with Statistical Methods

The possibility of measurement of subcriticality of reactors of nuclear power plants by statistical methods in the performance of requirements of Regulations NP-082-07 is discussed. The statistical methods, in particular, the Feynman method, make it possible to measure the subcriticality of shutdown reactors and at initial start-ups within the required range of 0.01–0.02 at the level of neutron detector counting of about one pulse per second. The Feynman method was perfected at the critical assembly of the high-temperature gas-cooled nuclear reactor PROTEUS at the Paul Scherrer Institute (Switzerland). The measurement results of subcriticality are presented. The conditions which should be ensured to obtain an acceptable result of experiment are formulated.     

堆振荡器法测量反应性的误差因素分析

为合理选择堆振荡器法实验条件,利用数值求解和公式推导,对影响测量精度的几项主要因素进行了分析。研究表明,通过选择合适的反应性振荡幅度及频率,可以提高堆振荡器法测量反应性的精度。由分析结果可知,对于中子代时间较短的反应堆,要使用堆振荡器法测量小反应性,在测量条件允许的情况下,应尽可能选择高频率的反应性振荡。     

White noise nonlinear system analysis in nuclear magnetic resonance spectroscopy

Nonlinear noise excitation in nuclear magnetic resonance is a form of nonlinear spectroscopy which exploits the nonlinear susceptibilities in a very direct way. The nonlinear susceptibilities are defined by perturbation theory in the frequency domain. In nonlinear system analysis, on the other hand, the system response is described by a Volterra series in the time domain. The kernels of the Volterra functionals carry the information about the system and are to be determined by experiment.The series expansion of a molecular, atomic or nuclear system response is derived in quantum mechanics by time dependent perturbation theory, leading to a Volterra series with time ordered, triangular kernels. The kernels are multi-dimensional products of decaying exponentials, which describe coherence decays of particular density matrix elements. The Fourier transforms of the triangular Volterra kernels are the susceptibilies, which are formally identical in NMR spectroscopy and nonlinear optical spectroscopy. The nonlinear susceptibilities are multi-dimensional spectra, which in NMR spectroscopy reveal the spin communication pathways. These are established by various forms of single quantum coherence connectivities, such as indirect coupling, chemical exchange, cross-relaxation, dipolar and quadrupolar coupling.If the functionals of the Volterra series are orthogonalized with respect to Gaussian white noise excitation, the Wiener series results. The Wiener kernels can be derived by multi-dimensional cross-correlation of the system response with different powers of the Gaussian white noise excitation.Cross-correlation of the transverse magnetization response to noise excitation in NMR leads to multi-dimensional time functions, the Fourier transforms of which closely resemble the nonlinear susceptibilities. The cross-correlation spectra differ from the susceptibilities in the governing Liouvillean and the dynamic density matrix, which are affected by saturation for continuous excitation. Cross-correlation spectra and susceptibilities converge for vanishing excitation power. Therefore the cross-correlation spectra are referred to as stochastic susceptibilities.In stochastic NMR spectroscopy only odd order susceptibilities exist for transverse magnetization. The first nonlinear order is the third, and the nonlinear spectral information is derived from the third order susceptibility. Higher order susceptibilities are not feasible to derive from experimental data. An important share of the nonlinear information is found on the six subdiagonal 2D cross-sections through the third order susceptibility. These cross-sections arise in three pairs, which carry distinct information, separated according to longitudinal magnetization and population effects, zero quantum coherences, and double quantum coherences.In practice a nonlinear 3D spectrum is computed from experimental data by an algorithm in the frequency domain, which yields access to selected regions in the 3D spectrum. This spectrum is the symmetrized stochastic third order susceptibility. All its sub-diagonal 2D cross-sections are equivalent. They are the average of the six different sub-diagonal 2D cross-sections through the asymmetric third order susceptibility.The stochastic excitation technique in NMR is characterized by several unique attributes. (1) There is no minimum time for a data acquisition cycle, so that, at the expense of signal-to-noise ratio, strong samples can be investigated faster with stochastic NMR than with pulsed FT NMR. (2) Stochastic excitation tests the sample extensively, and measures a maximum amount of information in a single experiment. This feature is of particular interest for investigation of short-lived samples and of samples with little a priori information. (3) An experiment with stochastic excitation is simple to perform, but the data processing is more complex than in FT spectroscopy. (4) The nonlinear information about spin communication pathways is derived for individual frequency regions only, which are identified in the stochastic ID spectrum. This information is located primarily on the sub-diagonal 2D cross-sections through the third order susceptibility. (5) Stochastic NMR spectra derived from random noise excitation are contaminated by systematic noise. In the sub-diagonal 2D cross-sections the noise is reduced by filtering and symmetrization during data processing. (6) Sub-diagonal 2D cross-sections are sensitive to experimental phase distortions in one direction only. They are readily adjusted in phase with the same parameters as the ID spectrum. (7) Stochastic multi-dimensional spectra can be computed at variable resolution from one and the same set of raw data.So far stochastic NMR spectroscopy is not applied routinely in analytical spectroscopy. More practical experience is needed to evaluate its merits in comparison with Fourier transform NMR.Stochastic excitation is distinguished from continuous wave and sparsely pulsed excitation by low input power in connection with large bandwidth. This important property cannot be exploited in high resolution NMR in liquids, because excitation power is not a restricting factor in this case. The situation is different in NMR imaging, where large field gradients require large bandwidths and the excitation power becomes a point of concern. For this reason stochastic RF excitation is being investigated in NMR imaging.The multi-dimensional cross-correlation functions obtained from random noise excitation generally are contaminated by systematic noise. The occurrence of systematic noise can be avoided if pseudo-random excitation is used in combination with a transformation of the system response to obtain the kernels. This technique is used successfully in Hadamard spectroscopy, where the linear Volterra kernel is the Hadamard transform of the linear response functional. Nonlinear transformations^(220,221) for retrieval of nonlinear kernels have not yet been realized in NMR spectroscopy.The cross-correlation technique underlying the data evaluation in stochastic nonlinear system analysis is equivalent to interferometry in optical spectroscopy. The Michelson interferometer is the most prominent optical correlator. The time resolution of the kernels derived by cross-correlation is determined by the inverse bandwidth of the excitation. With the Michelson interferometer a time resolution of 10⁻¹⁴ s is achieved in IR spectroscopy. Since the IR correlogramm is Fourier transformed for spectral analysis, the time resolution cannot be exploited otherwise. For analysis of fast time dependent processes a two-dimensional interferometer should be constructed, which performs a 2D cross-correlation of the system response to two in general different noise inputs. One input pumps the time dependent process, the other is used to investigate the time dependence spectroscopically. This technique is introduced by the name of ‘two-dimensional interferometry’. It uses low excitation power, but provides high time resolution at large response energy. Related work is pursued in nonlinear optical spectroscopy with incoherent excitation. In this area the use of broad band lasers is investigated for generation of echoes and for correlation based measurements of relaxation times.     

Electronic imaging system for neutron radiography at a low power research reactor

This paper describes an electronic imaging system for producing real time neutron radiography from a low power research reactor, which will allow inspections of samples with high efficiency, in terms of measuring time and result analysis. This system has been implanted because of its potential use in various scientific and industrial areas where neutron radiography with photographic film could not be applied. This real time system is installed in neutron radiography facility of Argonauta nuclear research reactor, at the Instituto de Engenharia Nuclear of the Comissão Nacional de Energia Nuclear, in Brazil. It is adequate to perform real time neutron radiography of static and dynamic events of samples.     

Analysis of Pulse Tolerance to Pump Depletion Induced Noise in DWDM Systems Using Distributed Fiber Raman Amplifiers

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SiC基中子探测器对热中子的响应

以SiC二极管和中子转换材料6LiF为基础,研制了SiC基中子探测器,并用241Am源与临界装置分别研究了SiC基中子探测器的粒子响应、热中子响应。结果表明:SiC基中子探测器能够满足241Am源粒子的计数测量,但由于SiC二极管灵敏区薄,故不能用于5.48 MeV的粒子能谱测量;SiC基中子探测器对热中子响应良好,不同功率下,脉冲幅度谱中可清晰看到由6Li(n,)3H的反应产物粒子、3H粒子形成的双峰;脉冲幅度甄别法可将射线及电子学噪声甄别掉;在直接测量与符合测量中,SiC基中子探测器的计数率均与临界装置功率成线性关系,且直接测量的线性度比符合测量的线性度好,最好可达0.999 97。研究表明:降低肖特基接触金属的厚度、增加其外延层厚度、提高其外延层品质,可将SiC二极管用于带电粒子能谱测量。