Mass Of Loose Part Research Articles

Bending Wave Propagation Analysis Induced by Metal Ball Impacts on Reactor Pressure Boundary Structure

Recently, a model-based prognostic approach is becoming one of noticeable techniques to predict the fault behaviors of mechanical components in nuclear power plant. Lamb’s general solution for an arbitrary impact force function and Hertz impact theory have been used to identify the bending wave characteristics impacted by a metallic loose part in reactor pressure boundary components. However. these approaches can hardly provide an information on accurate acceleration response for identifying the impact source. In this study, the impact response characteristics such as maximum acceleration amplitude and primary frequency of the impact response signal by a simulated loose part (metal ball) are analyzed using finite element analysis (FEA) and the FEA-based model is verified by experimental results. It is expected that the developed FEA-based model can be utilized in model-based prognostics for localization and estimation of mass of loose part in nuclear power plants.

Mass estimation of loose parts in nuclear power plant based on multiple regression

According to the application of the Hilbert–Huang transform to the non-stationary signal and the relation between the mass of loose parts in nuclear power plant and corresponding frequency content, a new method for loose part mass estimation based on the marginal Hilbert–Huang spectrum (MHS) and multiple regression is proposed in this paper. The frequency spectrum of a loose part in a nuclear power plant can be expressed by the MHS. The multiple regression model that is constructed by the MHS feature of the impact signals for mass estimation is used to predict the unknown masses of a loose part. A simulated experiment verified that the method is feasible and the errors of the results are acceptable.

A Method for Mass Estimation of Loose Parts in Nuclear Power Plant Based on Support Vector Machine

A new method for mass estimation of loose parts in nuclear power plant (NPP) based on the support vector machine (SVM) was proposed. It includes analyses of the relationship between the impact signals’ frequency spectrum and the mass of loose part, then formation of a vector consisting of linear predictive coding (LPC) parameters, which represent the shape of spectrum of impact signal. Using the vector as input data and the mass of loose part as the output data to train the SVM, the mass estimation can be done by the trained SVM model. Experimental results show that the method has higher accuracy and easier to achieve than the traditional methods. It provides a new way for mass estimation of loose part in NPP.

Loose-part mass and energy estimation

Expressions for loose-part momentum and impact force were derived as functions of plate bending wave surface acceleration and primary frequency content. These relationships were used to constrain the loose-part diagnostic problem so that loose part mass and impact energy can be determined for credible values of contact radius. Uncertainties associated with unknown contact radius were evaluated by simulation, and experimental data were analyzed for multiple energy impacts by metal spheres having mass between 0.15 and 32 lbs. Significant biases were found to exist when using apparent impact contact time information based on the two-dimensional Lamb wave model. Using the mass estimation method and bias estimates, an iterative technique was developed that converges to close to the theoretical contact time. The results provide methods for loose-part mass and energy estimation and for evaluating the effects of uncertainty in loose part location and signal transmission attenuation.

Loose-part signal properties

Lamb's solution for two-dimensional wave propagation was used to identify plate bending wave characteristics observed in loose part impact signals. The surface displacement wave is shown to have large second derivatives at points that can be used to measure the impact contact time. General features of the initial impact wave shape provide guidance for the use of spectral analysis techniques to identify the contact time and wave arrival time when there is a low signal-to-noise ratio. Improvements in the determination of contact time improve the estimation of loose part mass and energy through the Hertz impact parameters. The shape of the initial impact wave shape can also be used to identify on which side of the plate the impact took place. This information has applications for Loose Part Monitoring System metal impact signal validation and for improved estimation of loose part parameters.

Acceleration signal characteristics for loose part impact.

Characteristics of acceleration frequency spectra for an impact signal were studied and loose part mass was estimated, using variation in the frequency spectral patterns. The frequency spectral pattern for the acceleration induced by impact depends on the loose part mass and not on the impact energy and the loose part shape. It was found that the frequency spectral pattern for an impact which occurred at the lower plenum vessel wall is not influenced by the impact point. On the other hand, the maximum acceleration amplitude depends not only on the loose part mass but also on the impact energy, the loose part shape and the distance from the impact point. It was also found that the foremost portion of the accelerometer output signal is influenced by the impact force between a loose part and the vessel. However, a second portion is influeuced by the sensor resonance and structural resonances. Loose part mass estimation, using “FR” values (ratio between low frequency component and high frequency component), is useful. The uncertainty range for the estimated loose part mass is about 0.7 decade.

Studies on the loose part evaluation technique

In nuclear power plants, a loose part can contribute to component damage and material wear by frequent impacting with other parts in the system. Detection of loose parts is very important for plants, and location and mass evaluation of the loose part is also important after detection of loose parts. In this study, the fundamental characteristics concerning the impact wave propagation speed, the maximum acceleration amplitude, and frequency spectra of the impact signal for the simulated loose parts were studied. These characteristics have been applied to the impact location, and the loose part mass estimation. It was confirmed that the “MESH” method, to estimate the impact position, and the loose part mass estimation by “FR” value, show good results.