Relatively a large number of pipe failures in a nuclear power plant occur in a multi-component region such as the bends, the orifices and so on. Especially, it has been reported that FAC (Flow Accelerated Corrosion) frequently occurs in a multi-elbow. In this study, therefore, a complex flow structure in a s-shaped dual elbow is observed by using a PIV system to clarify the flow structure. The diameter of the elbow D is 56mm and the curvature radius rate y (=R/D,where Re is a curvature radius) is 1.5. A f...
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Clarification of complex flow structure in dual elbow

In this study, a new simulation method is developed for optimization of maintenance strategy in NPP as a multiple-objective optimization problem (MOP). The result of operation is evaluated as the average of the following three measures in 3 000trials: Cost of Electricity (COE) as economic risk, Frequency of unplanned shutdown as plant reliability, and Unavailability of Regular Service System (RSS) and Engineering Safety Features (ESF) as safety measures. The following maintena nce parameters are considered...
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Development of an evaluation method for optimization of maintenance strategy in commercial plant

Abstract The purpose of this study is to develop a method for quantitative evaluation of the running cost and safety in a Nuclear Power Plant (NPP). A new model for numerical evaluation is proposed based on the concept where the four issues such as Cost of Electricity (COE), maintenan ce cost, loss by the failures, and several risks are evaluated statistically by using the Monte Carlo simulation. The results show different d ependence on the parameters used in the model. These results would be useful to d...
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Development of quantitative evaluation method for the cost and safetyin maintenance plan of Nuclear Power Plant

In nuclear power plants, there are many T-junctions at which different temperature fluids are mixed. When the fluids with different temperature are mixed, temperature fluctu ation in fluids reachs wall and high-cycle heat fatigue occurs. Depending on amplitude and frequency of temperature fluctuation, it could lead to pipe rupture accident at wo rst. In addition, in case of the T-junction with 90-degreee bend at upstream, there is higher risk for pipe rupture accident due to secondary flow which arises in ...
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Effect of secondary flow generated in 90-dgree bend upon high-cycle thermal fatigue in a mixing tee

In a process of hot and cold fluid mixing, temperature fluctuation in the fluid can occur. When this fluctuation is caused by unstable fluid mixing process, the surrounding structure would be damaged by high-cycle thermal fatigue. This phenomenon is observed in various nuclear power plants, which means it is important to investigate the relation between the fluid mixing process and the thermal fatigue. When there exists a 90-degree bend i n the upstream of the mixing area, the fluid mixing process becomes ...
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Estimation on the thermal hydraulic characteristics in a non-isothermal fluid mixing

This work addresses LDI (Liquid Droplet Impingement) accompanied with pipe wall thinning in nuclear and thermal power plant s. In order to clarify the factors that affect the wall thinning, the structure of supersonic two-phase flow after an orifi ce is visualized with a digital video camera. The visualization experiment proves that the droplets impinges the pipe wall shortly after the orifice and that the amount of water droplets that passes through the orifice is the important parameter....
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Evaluation of Liquid Droplets Impact Erosion in downstream areas of an orificecaused by supersonic two-phase flow

Pipe wall thinning is one of the most important technical problems in nuclear power plants. For example, the wall thinning occurs by two-phase flow at both the orifice downstream and the first elbow located downstream after the orifice. In this study, a visualization experiment was conducted in order to clarify the detailed mechanism of the wall thinning by erosion (LDI is expected) in the piping system consisting of an orifice, a straight pipe and an elbow.In the experiment a strong pressure at the down ...
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Analysis (2) of Liquid Droplets Impact Erosion at the orifice downstream area caused by supersonictwo-phase flow

Abstract The NDT method using electromagnetic waves has the possibility to detect widely and quickly inner surface crack existin g in large pipes. The purpose of this study is to demonstrate validity of the method to detect the thin crack introduced by pla sma discharge fabrication. Through this study, it has been shown that both reflected and transmitted waves carry a lot of inform ation on existence of the crack. Experimental results indicate that there exists attractive possibility in this new NDT metho...
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Development of crack detection method by using electromagnetic wave