A feature selection method combined with ridge regression and recursive feature elimination in quantitative analysis of laser induced breakdown spectroscopy

In the spectral analysis of laser-induced breakdown spectroscopy,abundant characteristic spectral lines and severe interference information exist simultaneously in the original spectral data.Here,a feature selection method called recursive feature elimination based on ridge regression(Ridge-RFE) for the original spectral data is recommended to make full use of the valid information of spectra.In the Ridge-RFE method,the absolute value of the ridge regression coefficient was used as a criterion to screen spectral characteristic,the feature with the absolute value of minimum weight in the input subset features was removed by recursive feature elimination(RFE),and the selected features were used as inputs of the partial least squares regression(PLS) model.The Ridge-RFE method based PLS model was used to measure the Fe,Si,Mg,Cu,Zn and Mn for 51 aluminum alloy samples,and the results showed that the root mean square error of prediction decreased greatly compared to the PLS model with full spectrum as input.The overall results demonstrate that the Ridge-RFE method is more efficient to extract the redundant features,make PLS model for better quantitative analysis results and improve model generalization ability.     

Use of power spectral density in deriving response spectral shapes for aseismic design

Mean and mean + σ response spectral shapes based on accelerograms normalized to their respective peak ground acceleration (PGA) values have been widely used in the aseismic design of critical structures such as nuclear power plants. The computation of response spectral shapes based on accelerograms normalized to their respective power spectral densities (PSDs) has been proposed. A comparison of response spectral shapes using the two alternative normalization parameters (PGA and PSD) has been presented to demonstrate that the ordinates of the PSD-based mean + σ spectral shapes, which are better representatives of earthquake vibrations, are considerably lower than those of the PGA-based spectral shapes. The mean spectral shapes in the two cases are very close to each other, suggesting that a large part of the scatter in the PGA-based shapes is attributable to the procedure adopted for normalization of the accelerogram. The PSD-based spectral shapes can play an effective role in determining the margins available in the aseismic design of structures using the PGA-based mean + σ spectral shapes. Smooth response spectral shapes based on normalization with respect to the PSD are given for rock and soil sites at the end of the paper.     

Three-dimensional transient sealing analysis of the bolted flange connections of reactor pressure vessel

The failure of sealing system of the bolt flange connections is the primary failure mode of the nuclear reactor pressure vessel (RPV). For the safety and integrity of RPV, it is important to predict the sealing behaviour of the bolt flange connections under various loading conditions. Based on the finite element (FE) method for coupled thermal elastoplastic contact problems, a three-dimensional (3D) transient sealing analysis program of nuclear reactor pressure vessels is developed with the consideration of the non-linearity from both surface and material, transient heat transfer and multiple coupled effects. A contact correction approach is proposed to simulate the loading of the bolt connection under the condition of pre-stressing. An automatic pre-processing program is developed for FE modelling of RPVs. Using these programs, a 1:4 scaled model of a 300 MW RPV is analyzed under the loading conditions including pre-stressing, pressurization, heating and cooling. The computational results obtained are in a good agreement with the data of experimental tests. These programs are also successfully used in analyzing the full-scale model of the RPV in a nuclear power plant.     

Dynamic analysis of a nuclear reactor with fluid–structure interaction: Part I: Seismic loading, fluid added mass and added stiffness effects

The present paper is related to the dynamic (seismic) analysis of a naval propulsion ground prototype (land-based) nuclear reactor with fluid–structure interaction modelling. Many numerical methods have been proposed over the past years to take fluid–structure phenomenon into account in various engineering domains, among which nuclear engineering in seismic analysis. The purpose of the present paper is to make a comparative study of these methods on an industrial case, namely the pressure vessel and internals of a nuclear reactor. A simplified model of the pressure vessel and the internal structure is presented; fluid–structure interaction is characterised by added mass, added stiffness and coupling effects. The basic principles of the mathematical techniques for fluid–structure modelling and dynamic methods used in the analysis are first presented and then applied to compute the eigenmodes and the dynamic response of the fluid–structure coupled system with various numerical procedures (quasi-static, spectral and temporal approaches). Numerical results are presented and discussed; fluid–structure interaction effects are highlighted. As a main conclusion, added mass effects are proved to have a significant influence on the dynamic response of the nuclear reactor.     

Elastic–plastic analysis of nuclear structures with millions of DOFs using the hierarchical domain decomposition method

The hierarchical domain decomposition method (HDDM) proposed by Comp. Sys. Eng. 4 (1993) 495 is applied to the large scale elastic–plastic finite element (FE) analysis of nuclear structures. The HDDM is a method to implement the finite element method (FEM) on various kinds of parallel environments. The substructure-based iterative methods can effectively be used with the HDDM to solve the large scale linear algebraic equations derived from the implicit FEM. In this paper, some key techniques to parallelize the static elastic–plastic FE analysis by the HDDM are described. As illustrative examples, a support structure of the high temperature engineering test reactor (HTTR), a pressure vessel, and an internal pump of a pressure vessel are analyzed. The structure of HTTR and the pressure vessel are modeled by hexahedral solid elements whose total degrees of freedom (DOFs) are about 1.3 millions (M) and 3 M, respectively. The internal pump is modeled by quadratic tetrahedral elements whose total DOFs are about 2 M. The elastic–plastic analysis of a simple cube with 10 M DOFs is also carried out. Both the conjugate gradient method for solving the linear equations and the Newton–Raphson method for solving nonlinear problems successfully converge.     

Fluid-structure interaction analysis of a hypothetical core disruptive accident in LMFBRs

To ensure safety, it is necessary to assess the integrity of a reactor vessel of liquid-metal fast breeder reactor (LMFBR) under HCDA. Several important problems for a fluid-structural interaction analysis of HCDA are discussed in the present paper. Various loading models of hypothetical core disruptive accident (HCDA) are compared and the polytropic processes of idea gas (PPIG) law is recommended. In order to define a limited total energy release, a “5% truncation criterion” is suggested. The relationship of initial pressure of gas bubble and the total energy release is given. To track the moving interfaces and to avoid the severe mesh distortion an arbitrary Lagrangrian–Eulerian (ALE) approach is adopted in the finite element modeling (FEM) analysis. Liquid separation and splash from a free surface are discussed. By using an elasticity solution under locally uniform pressure, two simplified analytical solutions for 3D and axi-symmetric case of the liquid impact pressure on roof slab are derived. An axi-symmetric finite elements code FRHCDA for fluid-structure interaction analysis of hypothetical core disruptive accident in LMFBR is developed. The CONT benchmark problem is calculated. The numerical results agree well with those from published papers.     

Response of nuclear structural systems to transient and random excitations, using both deterministic and probabilistic methods

The finite element is commonly used for the static analysis of reactor components and the same ideas can be applied to the dynamic analysis. The formation of various damping matrices for both internal and external damping is discussed. For the most part only the linearized form of the equations of motion is considered giving

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. The type of solution adopted depends upon both the force input and the required response. For a short period transient input usually only the initial response is required which is best found from a step-by-step integration. A method involving a Taylor series and curve fitting over a series of steps is developed and applied to the solution of a beam subject to a pressure transient.For a periodic force input the steady state response is needed requiring the determination of the damped eigenvectors. An efficient algorithm, using the undamped vectors, is given and the response to an arbitrary force input developed. This method is applied to the previous example and the two solutions are compared illustrating the advantages and disadvantages of each method. For random excitation methods of presenting information are discussed standard results for the stationary problem are presented in terms of the first part of the paper. As an example the spectral density of the response due to random imposed movements is given illustrated by a series of heat exchange tubes excited by random forces. The response due to a non-stationary force input such as an earthquake is discussed. The step-by-step method of analysis is used to predict the probability density function of the response of a simple system at any time under such a non-stationary input. Possible modes of failure with reference to reactor components are discussed and indications of how the proceeding theory can be applied to predicting failures are given.     

An approximative solution for limit load of piping branch junctions with circumferential crack and finite element validation

This paper is concerned with the prediction of limit load of the piping branch junctions with circumferential crack under internal pressure. Recently, we have developed a new approach for predicting the limit load of two-cylinder intersection structures with diameter ratio larger than 0.5, which has been successfully applied to defect free cases under various loading conditions. In the present work, we consider the extension of the approach to cover cracked piping branch junctions. On the basis of stress analysis in the vicinity of intersection line, a closed form of limit load solution for piping branch junctions with circumferential crack was developed. Then, 36 finite element (FE) models of piping branch junction with various dimensions of structure and crack were analyzed by using nonlinear finite element software. The limit loads from FE analysis and the proposed solution are compared with each other. Overall good agreement between the estimated solutions and the FE results provides confidence in the use of the proposed formulae for defect assessment of piping branch junctions in practice.     

Observation of coherent mode induced by a molybdenum dust on EAST

The influence of a molybdenum dust buildup on plasma edge turbulence has been studied in the EAST tokamak.The motion of the dust from the upper divertor region is detected by a fast visible CCD camera,the XUV spectrometer arrays,and the EUV spectrometer.The MoXV emission intensity sharply increases compared with the spectral lines of various ionization states of other elements,which implies that the dust particles are the molybdenum impurities.The radial distribution of Mo14+ion simulated by a simplified 1D transport model indicates that the molybdenum dust mainly deposits in the pedestal bottom region.Moreover,it is observed that the coherent mode(CM)appears at ρ=0.94 after the molybdenum impurities enter the main plasma region.The influx of molybdenum impurities results in increasing pedestal electron density and decreasing pedestal electron temperature in contrast to that before the event of impurities dropping.It is also found that the electron density gradient in the pedestal increases when the ablation of the molybdenum impurities is observed in the pedestal region.The qualitative experimental results indicate that the onset of CM is likely related to the increase of the density gradient and edge collisionality in the pedestal.In comparison to the density gradient,the enhancement of CM amplitude largely depends on the increase of the edge collisionality.     

钍归一化在盆地γ能谱资料处理中的应用

在应用γ能谱资料寻找砂岩型铀矿的过程中,要尽可能地消除非矿化因素引起的干扰,提取与铀矿化有关的信息。介绍了钍归一化的原理及特点,采用与矿化有关的元素迁移信息的钍归一化方法,分析了二连盆地东部的γ能谱资料,揭示了该区放射性元素的分布特征、地球化学作用和后期铀元素的迁移与富集。结合其他地质资料,分析了钾剩差的变异区(正、负高值区)及铀剩差正高值区形成的原因,同时指出了经过钍归一化处理所得到的铀剩差正高值区应为氧化与还原作用过渡带的直接指示,也是该区进一步寻找砂岩型铀矿的重要标志。     

Analysis of Pulverized Coal by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy （LIBS） has been used to detect atomic species in various enviromnents. The quantitative analysis （C, H, O, N and S） of representative coal samples are being carried out with LIBS, and the effects of particle size are analyzed. A powerful pulse Nd：YAG laser is focused on the coal sample at atmosphere pressure, and the emission spectra from laser-induced plasmas are measured by time-resolved spectroscopy, and the intensity of analyzed spectral lines is obtained through observing the laser plasma with a delay time of 0.4 #s. The experimental results show that the slope of calibration curve is nearly 1 when the concentration of the analyzed element is relatively low, and the slope of curve is nearly 0.5 when the concentration of C is higher than other elements. In addition, using the calibration-free model without self-absorption effect, the results show that the decreasing of particle size leads to an increase of the plasma temperature.     

硝酸溶液中铌的溶剂萃取研究——Ⅳ.钼对溶剂萃取铌的影响

在1mol/l HNO_3-1×10~(-8)mol/l Nb中加入5×10~(-5)-1×10~(-1)mol/l不同浓度的钼,分别用TBP,HDBP和7402季铵盐萃取铌,与水相不含钼相比较,观察到钼的存在对萃取铌有明显的影响。这影响主要表现在铌的萃取分配系数(D_(Nb))增加和萃取机理发生变化。对于不同的萃取剂,使D~(Nb)增加所需要的钼浓度亦不同,尤其是7402季铵盐萃取时受影响更为显著。还研究了萃取剂、硝酸及硝酸根等浓度与D_(Nb)的关系,并且讨论了萃取机理。     

Quantitative analysis of saindha salt using laser induced breakdown spectroscopy and cross-validation with ICP-MS

Saindha salt is considered to be more advantageous than the other edible salts for the patients suffering from diabetes,blood pressure and kidney diseases.To explore the constituent elements of this salt,laser induced breakdown spectroscopy(LIBS) has been exploited for its qualitative and quantitative analysis.The third harmonic(355 nm) of a Q-switched Nd:YAG laser has been used to produce the saindha salt plasma and the time integrated optical emission spectra were registered using a set of six miniature spectrometers covering the spectral range of 230-805 nm.The spectroscopic analysis of the emission spectra predominately revealed numerous neutral or singly ionized emission lines of Ca,Mg,Na,K,Fe,Sr,Si,Li and Al.The laser produced plasma was characterized by calculating the electron temperature from the Boltzmann plots and the electron number density from the Stark broadened line profile as a function of laser irradiance and distance from the target sample.The relative concentration of the constituent elements was extracted by the integrated line intensities of the strongest spectral line of each element using the self-calibration-LIBS(SC-LIBS) and one-line calibration free-LIBS(OLCF-LIBS) methods.For cross-validation,the LIBS results have been compared with that obtained from the inductively coupled plasma-mass spectroscopy(ICP-MS) showing good agreement.     

Reliability analysis of pipe whip impacts

A probability-based approach is presented as the integration of probabilistic methods and deterministic modelling based on the finite element method. An existing finite element software package was linked to an existing probabilistic package to analyse the complex mechanics that occur during the transient non-linear analysis of impact problems. This methodology is applied to a pipe whip analysis of a group-distribution-header, which results from a guillotine break, and subsequent impact with the adjacent building wall; this is a postulated accident for the Ignalina Nuclear Power Plant RBMK-1500 reactors. The uncertainties of material properties, component geometry data and loads were taken into consideration. The probabilities of failure of the impacted header and of the header support-wall were estimated given uncertainties in material properties, geometrical parameters and loading. The software ProFES was used for the probabilistic analysis and the finite element software NEPTUNE for deterministic structural integrity evaluation. The Monte Carlo Simulation, First Order Reliability method and Response Surface method were used in the probabilistic analysis.     

Numerical simulation of laser ablation of molybdenum target for laser-induced breakdown spectroscopic application

Laser-induced breakdown spectroscopy has been recognized as a significant tool for element diagnostics in plasma–wall interaction. In this work, a one-dimensional numerical model is developed to simulate the laser ablation processes of a molybdenum(Mo) target in vacuum conditions. The thermal process of the interaction between the ns-pulse laser with wavelength of 1064 nm and the Mo target is described by the heat conduction equation. The plasma plume generation and expansion are described by Euler equations, in which the conservation of mass density, momentum and energy are included. Saha equations are used to describe the local thermal equilibrium of electrons, Mo atoms,Mo~+ and Mo~(2+) Plasma shielding and emission are all considered in this model. The mainly numerical results are divided into three parts, as listed below.Firstly, the rule of the plasma shielding effect varying with laser intensity is demonstrated quantitatively and fitted with the Nelder function. Secondly, the key parameters of plasma plume,such as the number density of species, the propagation velocity and the temperature, are all calculated in this model. The results indicate that the propagation velocity of the plume center increased with time in a general trend, however, one valley value appeared at about 20 ns due to the pressure gradient near the target surface leading to negative plasma velocity. Thirdly, the persistent lines of a Mo atom in the wavelength range from 300 nm to 600 nm are selected and the spectrum is calculated. Moreover, the temporal evolutions of Mo's spectral lines at wavelength of 550.6494 nm,553.3031 nm and 557.0444 nm are given and the results are compared with experimental data in this work.     

On the systematic evaluation of the fracture safety,particularly for pressure vessels

A systematic evaluation of the fracture safety particularly for pressure vessels is presented. It is a stepwise approach based on the conventional brittle fracture test methods (qualitative assessment using temperature criteria) as well as on the current fracture mechanics test methods (quantitative assessment using LEFM-EPFM). The important aspects in connection with the application of the quantitative assessment, e.g. material and fracture mechanics properties, specimen types, test and fracture mechanics analysis methods are discussed. Also results of a fracture mechanics test program for a reactor pressure vessel are shown and the importance and the difficulties to acquire component specific fracture mechanics properties are described.     

Dynamic analysis of the NPP pressure sensor system

The aim of the work was to develop on-line methods of control and diagnostics of pressure sensors at a NPP. The analysis was carried out along two lines:

1. i) The detection system including the sensor itself was modeled theoretically to obtain and study its transfer function, and to establish correspondence between the spectral characteristics of the pressure signal.

2. ii) The numerical processing of the signal using the AR technique to reconstruct the transfer function and evaluate the system's response, to a step impulse, as well as the spectral analysis. The hydraulic model presented indicate that the spectral lines observed at 10 Hz are due to longitu-dinal oscillations of water in the system branches, while the response time of the detection system is effectively the time of signal retardation in the porous ceramic diaphragms of the δ-cell of the sensor itself.

     

Coupling effect between liquid sloshing and flexible fluid-filled systems

Current practice in seismic design of flexible liquid-filled systems is reviewed. A coupled fluid-structure finite element method which considers the sloshing effect is developed for the seismic analysis of liquid-filled systems of various geometries with and without internal components. An analysis of the dynamic interaction between the structural vibration and liquid sloshing is also presented. Both rigid and flexible fluid-tank systems of different configurations are considered. Results demonstrate that tank flexibility can affect the amplitude of the free surface wave and hence the sloshing pressure and structural response. This result is consistent with the perturbation analysis. The dynamic interaction depends on (1) the ratio of natural frequency between fluid sloshing and the fluid-tank system and (2) the ratio of the effective areas of the fluid-structure interface and free surface of the fluid. Hence it is expected that in analyzing tanks with flexible internal components, this coupling effect can be more pronounced.     

LOCA工况下环形燃料元件内包壳外压屈曲试验研究

环形燃料一种安全高效的新型核燃料。为对环形燃料元件冷却剂丧失事故（LOCA）下整体受压失效形式的问题进行研究,将环形电加热棒、模拟芯块和试验件组装成试验装置,在空气环境中,以环形电加热棒外加热的方式,对环形燃料元件内包壳进行了外压屈曲试验,并将试验屈曲压力与Bresse?Bryan公式计算结果和特征值屈曲数值模拟分析结果进行了对比分析。结果表明：Bresse?Bryan公式计算结果除以安全系数m=2?5得到的结果高于试验结果而不够保守,试验结果分布于特征值屈曲数值模拟分析结果的1/5?1/3之间。本文结果可为环形燃料元件安全评价及后续工程化提供基础数据。     

Development of an Automated LIBS Analytical Test System Integrated with Component Control and Spectrum Analysis Capabilities

The present paper proposes an automated Laser-Induced Breakdown Spectroscopy(LIBS) analytical test system,which consists of a LIBS measurement and control platform based on a modular design concept,and a LIBS qualitative spectrum analysis software and is developed in C#.The platform provides flexible interfacing and automated control;it is compatible with different manufacturer component models and is constructed in modularized form for easy expandability.During peak identification,a more robust peak identification method with improved stability in peak identification has been achieved by applying additional smoothing on the slope obtained by calculation before peak identification.For the purpose of element identification,an improved main lines analysis method,which detects all elements on the spectral peak to avoid omission of certain elements without strong spectral lines,is applied to element identification in the tested LIBS samples.This method also increases the identification speed.In this paper,actual applications have been carried out.According to tests,the analytical test system is compatible with components of various models made by different manufacturers.It can automatically control components to get experimental data and conduct filtering,peak identification and qualitative analysis,etc.on spectral data.