(Special) Structural health monitoring and diagnostic in nuclear power plant
Chair: Dr. Jinho Park (Korea Atomic Energy Research Institute)
Measurement of Wavenumber of Wall-thinned Plate Using Spatial Local Wavenumber Filtering Dr. To KANG, Jeong Han LEE, Seong-In MOON, Soon-Woo HAN, Jin-Ho PARK, Gyuhae PARK and Jun Young JEON (Korea Atomic Energy Research Institute, Chonnam National University)
The surface of a shell-type structure can generate cracks or wall-thinning due to corrosion, etc. Those can eventually lead to the fracture of the structure, which can trigger enormous fatality and property loss. Thereby, a laser imaging technology on such structures as thin plate structure or piping whose thickness is relatively thin in comparison to the area, has been steadily studied for the past 10 years. The most typical among the laser imaging technology is the pulse laser imaging. By using the same, a new technology for inspecting and imaging a desired area within a relatively short period of time was developed, so as to scan various structures including the thin-plate structure and piping. However, this method builds image by measuring waves reflected from defects, and has a time delay of a few milliseconds at each scanning point. Moreover, complexity of the systems is so high due to additional components such as laser focusing parts. This paper proposes laser imaging method with increased scanning speed based on excitation and measurement of standing waves in structures. It is shown that defects in a structure can be visualized by generating standing waves with single frequency and scanning the waves at each point by the laser scanning system suggested in this work. To quantitatively evaluate thickness of a plate, wavenumber is calculated by acoustic wavenumber spectroscopy, and relationship between wavenumber and thickness of the plate is established by Rayleigh-Lamb frequency equation. The proposed technique is validated by wall-thinned plates that have constant wall loss and a linear thickness variation wall loss.
A Study on Acoustic Signal Processing Technique for Detecting Small Leak of Piping System Dr. DOOBYUNG YOON, SOONSUNG MOON and BONGSOO YANG (KAERI)
The importance of the leak detection of a pipe in a power plant of Korea is being emphasized as the pipes of a power plant are more than 20 years old. The objective of this work is to develop a signal processing technique for detecting small leak of piping system in a noisy environment. For this purpose, as algorithms for enhancing the leak detection capability, a small leak detection algorithm were developed by using time-spatial characteristics of the measured acoustic signal. The leak detection capability of the developed algorithm is verified by experiments and numerical simulations. It is expected that the developed small leak detection algorithm can be utilized for leak detection of piping system of a power plant.
Development of experimental metal sphere-mass map of reactor vessel scale models Dr. Soon-Woo HAN, Seong-Il LEE, Jeong-Han LEE and Jin-Ho PARK (Korea Atomic Energy Research Institute)
Loose parts in coolant systems of a nuclear power plant (NPP) can damage structural integrity of the systems and loose part signals monitoring systems (LPMS) are installed in most of NPPs. LPMS detect impact signal of a loose part and generate alarm if amplitude of the signal is over preset level. If impact signal detected, mass estimation of the loose part must be carried out in order to see the effect of the part impact on structural integrity. A metal sphere-mass map, which shows relations between amplitude and center frequency of impact signals according to mass, is essential in mass evaluation of a loose part and the map built for US NPPs has been used so far. For the purpose of precise impact analysis suitable for Korean NPPs, this work discusses the development of a mass map of Korean Standard Nuclear Power Plant (KSNP) based on experimental data for scale models of a KSNP reactor vessel as tests for real NPP vessels under operation is actually impossible. Impact tests were carried out for scale models by using metal sphere with various mass and velocity. Amplitudes and center frequencies of impact signals were investigated based on time-frequency analysis and the mass map for each models were constructed based on the results. Blind tests were additionally implemented with metal sphere with unknown mass and velocity and verified feasibility of the proposed metal sphere mass map.
Bending Wave Propagation Analysis induced by Metal Ball Impacts on Reactor Pressure Boundary Structure Dr. SeongIn MOON, To KANG, Seong-Il LEE, Jung-Seok SEO, Jeong-Han LEE, Soon-Woo HAN and Jin-Ho PARK (Korea Atomic Energy Research Institute)
Recently, a model-based prognostic approach is becoming as 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 information on accurate acceleration response for identifying the impact source. In this study, the impact response characteristics such as the impact wave propagation velocity, the maximum acceleration amplitude, and the 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.