基于Labview技术的研究堆瞬发中子衰减常数α实验研究

利用反应堆互功率谱密度(CPSD)测试系统对300~#池式研究堆的瞬发中子衰减常数α进行实验研究。堆芯采用低富集度U燃料装载,燃料组件有一定燃耗。测试系统以PCI-6143高速同步数据采集卡(DAQ)为测试硬件,以Labview8.5程序为开发软件;利用紧靠堆芯对称布置的2路γ补偿电离室探测器获得中子在堆内的连续电流信号,该信号输入到测试系统后,再应用数据采集和数据处理分析程序得到互谱密度,最后用非线性最小二乘法拟合得到瞬发中子衰减常数α为(83.5±0.6)s~(-1),结果与实际运行的情况相符合,表明本次带燃耗的瞬发中子衰减常数α测量是成功的。     

300#反应堆瞬发中子衰减常数测量

利用反应堆噪声分析技术测量300^#池式研究堆缓发临界下的瞬发中子衰减常数。堆芯采用低富集度U燃料装载，燃料元件带一定燃耗。利用紧靠堆芯布置的两个中子探测器，信号经测量系统和相关软件得到互谱密度，用非线性最小二乘法拟合得到瞬发中子衰减常数。在4kW功率水平测得缓发临界下的瞬发中子衰减常数α_c=(83.4±0.7)s^.-1。     

柱形金属铀次临界系统瞬发中子衰减常数测量

次临界核系统的瞬发中子衰减常数α与反应性有着重要联系。采用²⁵²Cf随机脉冲源法测量了一柱形金属次临界系统的瞬发中子衰减常数。为对源中子的影响进行分析,借助蒙特卡罗模拟方法建立模型进行了模拟,对源直穿中子和核系统瞬发中子时间分布特性进行了比较,分析了源中子对瞬发中子衰减曲线的影响。模拟结果表明,对该柱形金属铀系统,源中子注入100 ns后源直穿中子对核系统瞬发中子的影响可忽略。根据分析结果选取了合理起始道,对实验数据进行单指数最小二乘拟合,得到该次临界系统的α为15.5μs^-1。     

内生脉冲中子源方法测量固态零功率堆的某些动态参数

用内生脉冲中子源方法测量固态零功率堆的瞬发中子衰减常数，从而得到不同装载下的反应堆次临界度，还给出了测量瞬发中子衰减常数所用的一些参量。     

脉冲堆瞬发负温度系数的噪声测量法

根据反应堆堆内中子信号和温度信号的相关性，以及中子动力学方程和热力学绝热方程，利用噪声信号分析技术，在频域内建立了测量脉冲堆堆芯瞬发负温度系数的物理模型，同时，利用反应堆稳态运行是中子信号以及温度信号和扰动信息，通过自回归滑动和ＡＲＭＡ模型，得到中子噪声信号以温度噪声信号的功率谱密度（ＰＳＤ）再在频域内，通过最优化方法得到脉冲堆堆芯瞬发负温度系数值，该值与理论值相符。     

用核噪声方法测量氢化锆零功率堆的瞬发中子衰减常数

瞬发中子衰减常数α是反应堆的重要动态参数,由次临界和临界状态下的瞬发中子衰减常数可以刻度出反应堆的次临界深度。在瞬发中子衰减常数的测量中,脉冲中子源方法是经常使用的非常成熟的方法。本文叙述另一种方法——核噪声方法测量瞬发中子衰减常数,这种方法使用中子探测器,探测堆内中子水平的涨落,通过对中子涨落信号的分析处理,导出瞬发中子衰减常数α。与脉冲中子源方法相比,核噪声方法的优点是测量方法简单,只需在反射层内放置中     

单次脉冲中子源方法测量瞬发中子衰减常数

瞬发中子衰减常数α是核系统的重要标志性特征参数,该值的准确测量对于核临界安全具有重要意义。本工作采用单次脉冲中子源的方法测量了某次临界核系统的瞬发中子衰减常数,获得了几种不同次临界状态下的瞬发中子衰减常数,测量结果与²⁵²Cf随机脉冲源法测量结果一致。     

准宏观中子噪声测量分析系统的开发

基于LabVIEW平台开发了反应堆准宏观中子噪声测量分析系统.布置在次临界反应堆附近的3 He计数管输出的中子脉冲信号,经过若干仪器模块和PCI - 6602数据采集卡,送入计算机,通过频谱分析可以得出次临界反应堆的瞬发中子衰减常数.该系统已经过实验的验证.     

基于中子噪声分析的某核电厂堆芯吊篮梁型振动特征研究

研究了基于堆外电离室中子噪声信号监测压水堆核电厂反应堆吊篮的方法,通过计算电离室中子噪声的互功率密度谱、相干和相位,分析得到了堆芯吊篮梁型振动的频率;利用该方法,计算获得了某正常运行状态下压水堆核电厂换料周期内堆芯吊篮梁型振动频率和中子噪声功率谱幅度的变化趋势,结果说明了在反应堆正常运行状态下,随着堆芯燃耗的增加,吊篮梁型振动频率发生了微小漂移,频率变小,该频率处中子噪声功率谱幅度变大。     

西安脉冲堆燃耗对中子代时间的影响研究

本文研究了计算反应堆中子代时间(Λ)的瞬发中子通量密度衰减法,基于反应堆仅释放瞬发中子的假设条件,研究了瞬发中子动力学方程,将Λ的计算转变为α本征值的计算问题,采用MCNP程序模拟瞬发中子通量密度的衰减特性以拟合出α值。该方法避免了抽样计算中子价值函数的复杂问题,实现相对容易。并根据西安脉冲堆(XAPR)堆芯三维燃耗分布拟合出不同燃耗深度下瞬发中子通量密度衰减系数α,计算出堆芯中子代时间。结果表明:随着XAPR堆芯燃耗的加深,中子代时间呈增大趋势,从新堆芯到第一循环末(120EFPD),Λ增大幅度为8.93%。     

Power spectral analysis for a thermal subcritical reactor system driven by a pulsed 14 MeV neutron source

A series of power spectral analyses for a thermal subcritical reactor system driven by a pulsed 14 MeV neutron source was carried out at Kyoto University Critical Assembly (KUCA), to determine the prompt-neutron decay constant of the accelerator-driven system (ADS). The cross-power spectral density between time-sequence signal data of two neutron detectors was composed of a familiar continuous reactor noise component and many delta-function-like peaks at the integral multiple of pulse repetition frequency. The prompt-neutron decay constant inferred from the reactor noise component of the cross-power spectral density was consistent with that obtained by a pulsed neutron experiment. However, the reactor noise component of the auto-power spectral density of each detector was hidden by a white chamber noise in the higher-frequency range and this feature resulted in a considerable underestimation of the decay constant. For several runs with a low pulse-repetition frequency, furthermore, we attempted to infer the decay constant from point data of the delta-function-like peaks. The analysis for a run under a slightly subcritical state resulted in the consistent decay constant; however, those for other runs under significantly subcritical states underestimated the decay constant. Considering the contribution of a spatially higher mode to the point data, the above underestimation was solved to obtain the consistent decay constant. While the Feynman-α formula for a pulsed neutron source is too complicated to be fitted directly to variance-to-mean ratio data, the present analysis on frequency domain is much simpler and the conventional formula based on the first-order reactor transfer function is available for fitting to power spectral density data.     

Preliminary measurements of the prompt neutron decay constant in MASURCA

Pulse counting techniques have been used to measure the prompt decay constant = (β - ) / Λ in the MASURCA reactor of CEA at critical state. The data has been analyzed in time domain using Rossi- and Feynman- techniques, and in frequency domain using the cross power spectral density.

The Rossi- technique has been studied using one and two detectors. Due to the strong inherent spontaneous fission source, the one-detector variant gives a very strong white-noise signal, which is absent in the two-detector method. Because each neutron detected recorded not only a pulse, but also an echo after 120 ns, corrections had to be made to the theory applied.

The Feynman- technique is even more sensitive to the echo in the signals, and quite large corrections had to be made. Nevertheless the results obtained are in reasonable agreement with those of the correlation methods. For both measurement techniques, experiments of long duration are needed to get accurate results. The results obtained agree within 10% with calculations.

The prompt decay constant has also been measured with a continuous current technique. From the cross power spectral density thus obtained, the -value is in agreement with that of the pulse counting techniques.     

Application of Polarity Correlation Method to Graphite Moderated Reactor

The polarity correlation method has been applied to an experiment for measuring the prompt mode neutron decay constant of a reactor with a long neutron lifetime. Measurements have been performed in the SHE VIII-l at critical and several subcritical steady states (0~ — 1$).

The analog signal of detector output is converted to a polarity signal having only one-bit of information on the amplitude of the detected signal. The polarity correlation function is obtained as the correlation function between two polarity signals. Attention has been paid in the design of the correlator to obtain ample stability in operation. Using a digital computer, the prompt mode neutron decay constant is determined with 2% experimental accuracy from the decay curve of the polarity correlation function. A series of the prompt mode neutron decay constants is fitted to an approximated expression of inhour equation to obtain βl. The value of each prompt mode neutron decay constant was found to be in good agreement with that measured by the pulsed neutron technique. The polarity correlation method is particularly applicable to critical or near critical state where a pulsed neutron source cannot be effectively introduced.

In Appendix, an estimation is made for the error in the measured polarity correlation function due to unbalanced mean setting level in the experiment.     

Monte Carlo simulation of Feynman-α and Rossi-α techniques for calculation of kinetic parameters of Tehran Research Reactor

Noise analysis techniques including Feynman-α (variance-to-mean) and Rossi-α (correlation) have been simulated by MCNP computer code to calculate the prompt neutron decay constant (α₀), effective delayed neutron fraction (β_eff) and neutron generation time (Λ) in a subcritical condition for the first operating core configuration of Tehran Research Reactor (TRR). The reactor core is considered to be in zero power (reactor power is less than 1 W) in the entire simulation process. The effect of some key parameters such as detector efficiency, detector position and its dead time on the results of simulation has been discussed as well. The results of proposed method in the current study are validated against both the experimental data and the results of MTR_PC computer code.     

Determination of prompt-neutron decay constant from phase shift between beam current and neutron detection signals for an accelerator-driven system in the Kyoto University Critical Assembly

A unique power spectral analysis for a subcritical reactor system driven by a pulsed 14 MeV neutron source was carried out at the Kyoto University Critical Assembly (KUCA). In this analysis, a complex cross-power spectral density between time-sequence signal data from an accelerator beam ammeter and a neutron detector was measured to determine the prompt-neutron decay constant of an accelerator-driven system (ADS) from the phase data of the spectral density. Assuming the one-point kinetics model, in theory, the decay constant can be arithmetically derived from the phase at the integral multiples of the pulse repetition frequency. However, the actual derivation from the phase at a pulse repetition frequency of 20 Hz considerably underestimated the prompt-neutron decay constant, compared with that obtained by a previous pulsed neutron experiment, and the derived decay constant apparently decreased with an increase in the multiple of the pulsed repetition frequency. Considering a lag time in detector response, the above underestimation and the above apparent decrease were solved to obtain the consistent decay constant. While both previous power spectral analysis and Feynman-α analysis for pulsed neutron source require non-linear least-squares fits of the respective complicated formulae, the present analysis makes the fitting unnecessary except at regular calibration of the lag time. This feature is advantageous for a robust online monitoring of subcritical reactivity of an actual ADS.     

252Cf源驱动噪声分析法测量α初步研究

在一球形浓缩铀临界装置上,采用²⁵²Cf源驱动噪声分析方法对其次缓发临界状态下的α进行测量,在频域内分析数据得到α。对比频域内的两种数据处理方式（功率谱实虚部相除方法和功率谱取模直接拟合方法）,用互功率谱密度函数实虚部相除方法得到在-0.1$情况下,脉冲堆的α为0.58μs^-1,与Rossi-α方法的结果相吻合。