Methodology of Nuclear Reactor Monitoring and Diagnostics Using Information Dimension Application to Power Oscillation

Abstract

Reactor noise analysis method based on information dimension is applied to the monitoring and diagnosing of power oscillation. The method focuses on the utilization of the slope of the correlation integral (SOCI) which determines the information dimension of attractors. For practical application, the information dimension is expected to be the same as the fractal dimension of attractors; it can be used to classify different asymptotic regimes of nonlinear dynamical systems. We examined a real power oscillation using SOCI and the results implied that the oscillation was just a noisy limit cycle, although it is not possible to assert that there is no chaotic character in the oscillation because large oscillatory time-series data sets are not available. In addition, the application of SOCI to the real-time monitoring of power oscillation is proposed and examined.     

核爆电磁脉冲信号的分形特征分析

针对核爆电磁脉冲(NEMP)信号的非平稳、非线性特点．将小波变换和分形方法引入到NEMP信号的分析处理中,提取了多分辨率能量分形特征及盒维数．并在实验的基础上对所提取的特征与NEMP传播距离及当量之间的关系进行了分析．从而为NEMP信号分析与处理提供了一种新的方法。     

Application of fractal characteristic quantities of pressure fluctuation in subcooled boiling regime recognition

The dynamical behavior of the subcooled boiling two-phase system was introduced and discussed.with the introduction of ractal concept,an analysis of the fractal feature of pressure wave signals from nonlinear dynamics point of view,was carried out.Meanwhile,the pseudo phase diagrams of typical time series of sound pressure were given.Finally,through dynamic clustering and on the asis of calculating correlation dimension and Hurst exponent of pressure wave time series on different subcooling conditions,the recognition of developing regime of the two-phase system was delivered,which might provide a promising approach of recognition and diagnosis of a boiling system.     

非线性动力学理论在反应堆噪声分析中的应用研究

利用非线性动力学理论，给出了反应堆噪声功率振荡的非线性特性的差别方法，并对实际信号进行了处理。结果表明热态模拟运行时，反应堆的功率振荡易发生Hopf分叉，圆周形吸引子是存在的，随机噪声会对维数产生较大的干扰，但基本未改变吸引子的形状。该方法对反应堆的详细分析有一定的实际意义。     

某花岗岩型铀矿田断裂构造的分形特征

基于分形理论,提出了一种快速测量多区断裂分维值的方法,并获得了研究区断裂分维值的平面等值图.研究结果表明,断裂分维值的大小较好地反映了断裂构造复杂程度的高低,它们之间存在着正相关关系.研究区花岗岩型铀矿田内约有86%的铀矿床位于断裂分维值D偏高(D＞1.18)的区域内,表明断裂分维值越大,越有利于花岗岩型铀矿成矿,为建立该区花岗岩型铀矿新的预测标志提供了参考依据.     

Numerical Study on Observed Decay Ratio of Coupled Neutronic-Thermal Hydraulic Instability in Ringhals Unit 1 under Random Noise Excitation

The core stability in the Ringhals Unit 1 was estimated under the numerical random noise that simulates indefinable two-phase flow noise sources in actual cores. This noise model is expressed as a product of band white amplitude and arbitrary shape functions. In evaluating decay ratios, the conventional free-decaying method based on a clean modal disturbance was replaced with the response analysis method based on a numerical moderator density noise. The stability monitoring procedure was reproduced numerically by giving the spatially random shaped noise disturbance and by linearly varying the moderator density reactivity multiplier. It was confirmed that the observed regional decay ratio based on differential LPRM signals proposed by Hagen sometimes shows a discontinuous jump from the stable to the unstable region as predicted by Pazsit. Nevertheless, the regional decay ratio based on the extracted modal response will show a continuous change under the same condition. It was clarified that this jumping is mainly induced by the local fluctuation of moderator density at the frequency range which overlaps with a predominance range of the fundamental mode. It was demonstrated that this kind of numerical noise analysis is useful in verifying the monitoring algorithm before applying it in actual plants.     

Nonlinear analysis for a nuclear-coupled two-phase natural circulation loop

The objective of this paper is to develop a nonlinear numerical model to investigate the stability and nonlinear dynamics of a nuclear-coupled two-phase natural circulation loop. Some stability maps, parametric effects and transient characteristics of this natural circulation loop have been studied. Results indicate that the system indeed has two instability regions, the type-I and type-II instabilities, as is well known for a natural circulation loop. Parameters may induce different effects on the system stability in type-I and type-II unstable regions. In particular, the void-reactivity feedback destabilizes the system in both regions of low and high operating powers. Moreover, by strengthening nuclear feedback effect, period-doubled bifurcation may prevail in the system at relatively high inlet subcoolings and eventually a chaotic attractor appears with a fractal dimension of 1.79 ± 0.01 and an embedding dimension of 5.     

Limitation of Burn Time due to Ash Accumulation in a Moving Ring Reactor

A new method for evaluating the decay ratios in a boiling water reactor (BWR) using the singular value decomposition (SVD) method had been proposed. In this method, a signal component closely related to the BWR stability can be extracted from independent components of the neutron noise signal decomposed by the SVD method. However, real-time stability monitoring by the SVD method requires an efficient procedure for screening such compoments. For efficient screening, an artificial neural network (ANN) with three layers was adopted. The trained ANN was actually applied to decomposed components of local power range monitor (LPRM) signals that were measured in stability experiments conducted in the Ringhals-1 BWR. In each LPRM signal, multiple candidates were screened from the decomposed components. However, decay ratios could be estimated by introducing appropriate criterions for selecting the most suitable component among the candidates. The estimated decay ratios are almost identical to those evaluated by visual screening in a previous study. The selected components commonly have the largest singular value, the largest decay ratio and the least squared fitting error among the candidates. By virtue of excellent screening performance of the trained ANN, the real-time stability monitoring by the SVD method can be applied in practice.     

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。     

甘肃北山预选区旧井地段断裂的分形特征--中国高放废物处置的潜在场址

以甘肃北山旧井地段的断裂为研究对象,对其进行了分形特征研究。在对该区的TM遥感影像进行线性构造解译的基础上,利用线性构造分布图,使用Box Flex方法,计算了旧井地段断裂的分维值,结果表明,旧井地段断裂具有分形特征,且分维值为1．466,在工程岩体质量分级中属于“好”的级别。通过此项研究,初步建立了旧井地段断裂分形特征的研究方法,评价了该地段花岗岩的岩体工程质量,为高放废物处置库的选址和场址评价提供了基础资料。     

基于分形盒维数的汽轮机转子振动故障诊断的实验研究

汽轮机转子是汽轮机故障预测及诊断问题的一个重要方面.利用振动信号或状态量对设备进行诊断,是设备故障诊断中最有效、最常用的方法.本文在Bently实验台上进行了实验,模拟电站汽轮机转子的不对中、不平衡、碰摩和轴承松动4种故障的振动过程.根据汽轮机故障的分形特征,采用分形盒维数方法进行了不同故障试验数据的分形盒维数研究计算.结果表明:碰摩状况下的轴心轨迹最为混乱且呈现雪花状,其对应的分形盒维数也最大;不平衡时的轴心轨迹较为平滑,其对应的分形盒维数最小;不对中故障及松动故障的分形盒维数居中.因此,分形盒维数在进行汽轮机转子故障类型诊断时有更好的区分度.     

铀矿堆浸分形动力学模型

本文采用堆浸铀矿石粒径分布分维数代替其平均粒径,对Mellado等提出的矿石堆浸动力学模型进行了改进。同时采用铀矿柱浸试验确定了铀矿堆浸分形动力学模型参数与堆浸铀矿石粒径分布分维数的关系,建立了铀矿堆浸分形动力学模型,并进一步采用柱浸试验对模型进行了验证。结果表明,所建立的铀矿堆浸分形动力学模型能很好地反映铀矿堆浸铀金属浸出的规律。     

压水堆堆芯非线性系统的全局稳定性分析

判定压水堆堆芯非线性系统的全局稳定性是待解决的问题。建立了压水堆堆芯非线性系统,利用微小摄动方法求取其线性化模型。依据基于平衡流型的堆芯非线性测度在功率水平域内的分布情况,选择7个功率水平处的线性化模型作为堆芯局部模型,以局部模型组合来近似替代堆芯非线性系统。利用Lyapunov稳定性理论,分析堆芯非线性系统全局稳定性。计算结果表明：压水堆堆芯非线性系统是全局渐进稳定的;在判定堆芯系统全局稳定性时,这种非线性系统的建模方法是有效可行的。     

反应堆冷却剂系统非线性地震分析方法研究

通过理论研究并结合反应堆冷却剂系统中的非线性因素,提出了采用虚拟激励和模态叠加相结合的非线性地震分析方法进行反应堆冷却剂系统地震分析,该方法能够避免阻尼比选取存在的问题,同时又考虑了非线性因素.     

介孔氧化硅的分形特征

介孔氧化硅广泛应用于催化、吸附、分离中。将介孔氧化硅进行有机官能化则可改善其孔道表面性能。应用同步辐射小角x射线散射(SAXS)研究了纯介孔氧化硅和有机官能化介孔氧化硅的分形特征,结果表明它们均具有两种分形结构,即表面分形和孔分形。同时探讨了分形维数随样品制备条件的变化规律。     

An improved Feynman-α analysis with a moving–bunching technique

The bunching technique has been widely utilized in Feynman-α neutron correlation analysis to synthesize neutron counts within longer gate widths by bunching time-sequence neutron counts stored in multichannel scaler channels. An alternative technique referred to as “moving–bunching technique” was proposed to reduce a statistical scatter of variance-to-mean ratio of neutron counts. The conventional bunching technique has no overlap of adjacent bunches, while the present technique makes adjacent bunches overlap as long as possible similarly to the moving average technique. A Feynman-α experiment was performed in the UTR-KINKI, to confirm the advantage of the proposed bunching technique. When a neutron detector was placed far from the core, a Feynman-α analysis with the conventional bunching technique led to a scattered variance-to-mean ratio from which the prompt-neutron decay constant was never determinable. However, another analysis with the proposed technique remarkably reduced the above scatter and enabled the determination of the decay constant. For a neutron detector close to the core, the proposed technique also reduced statistical error of the decay constant.     

基于频域法超临界水冷堆CSR1000流动不稳定性研究

基于频域法研究了超临界水冷堆CSR1000的流动不稳定性。建立了CSR1000的堆芯数学模型,并利用开发的程序FREDO-CSR1000分析了堆芯平均通道和热通道在额定功率和流量范围内的流动不稳定性,得到衰减率、合适的进口阻力系数及超临界水堆的稳定运行区域。计算结果表明：在堆芯额定功率和流量范围内,第1流程的衰减率是单调变化的,第2流程因受进口温度的影响会出现急剧上升和急剧下降的趋势。     

Design evaluation of decay tank for a pool-type research reactor from the required minimum flow residence time point of view

A decay tank shall be designed to provide enough flow residence time to ensure that the N-16 activity decreases before the coolant leaves the decay tank's shielding room. However, when a proper criterion for the flow residence time in a decay tank is not presented, the tank would be oversized/undersized. In this paper, design evaluation for a decay tank is performed by investigating the effect of the fluid distribution along the residence time on the total dose rate and the required minimum flow residence time. The evaluation is also carried out to resize the predesigned decay tank.     

The effectiveness of full actinide recycle as a nuclear waste management strategy when implemented over a limited timeframe – Part II: Thorium fuel cycle

Full recycling of transuranic (TRU) isotopes can in theory lead to a reduction in repository radiotoxicity to reference levels in as little as ∼500 years provided reprocessing and fuel fabrication losses are limited. However, over a limited timeframe, the radiotoxicity of the ‘final’ core can dominate over reprocessing losses, leading to a much lower reduction in radiotoxicity compared to that achievable at equilibrium. In Part I of this paper, TRU recycle over up to 5 generations of light water reactors (LWRs) or sodium-cooled fast reactors (SFRs) is considered for uranium (U) fuel cycles. With full actinide recycling, at least 6 generations of SFRs are required in a gradual phase-out of nuclear power to achieve transmutation performance approaching the theoretical equilibrium performance. U-fuelled SFRs operating a break-even fuel cycle are not particularly effective at reducing repository radiotoxicity as the final core load dominates over a very long timeframe. In this paper, the analysis is extended to the thorium (Th) fuel cycle. Closed Th-based fuel cycles are well known to have lower equilibrium radiotoxicity than U-based fuel cycles but the time taken to reach equilibrium is generally very long. Th burner fuel cycles with SFRs are found to result in very similar radiotoxicity to U burner fuel cycles with SFRs for one less generation of reactors, provided that protactinium (Pa) is recycled. Th-fuelled reduced-moderation boiling water reactors (RBWRs) are also considered, but for burner fuel cycles their performance is substantially worse, with the waste taking ∼3–5 times longer to decay to the reference level than for Th-fuelled SFRs with the same number of generations. Th break-even fuel cycles require ∼3 generations of operation before their waste radiotoxicity benefits result in decay to the reference level in ∼1000 years. While this is a very long timeframe, it is roughly half that required for waste from the Th or U burner fuel cycle to decay to the reference level, and less than a tenth that required for the U break-even fuel cycle. The improved performance over burner fuel cycles is due to a more substantial contribution of energy generated by ²³³U leading to lower radiotoxicity per unit energy generation. To some extent this an argument based on how the radiotoxicity is normalised: operating a break-even fuel cycle rather than phasing out nuclear power using a burner fuel cycle results in higher repository radiotoxicity in absolute terms. The advantage of Th break-even fuel cycles is also contingent on recycling Pa, and reprocessing losses are significant also for a small number of generations due to the need to effectively burn down the TRU. The integrated decay heat over the scenario timeframe is almost twice as high for a break-even Th fuel cycle than a break-even U fuel cycle when using SFRs, as a result of much higher ⁹⁰Sr production, which subsequently decays into ⁹⁰Y. The peak decay heat is comparable. As decay heat at vitrification and repository decay heat affect repository sizing, this may weaken the argument for the Th cycle.