Abstract
In this study, a new method of estimating the leakage positions of cooling water using a stereo camera for the Fukushima Daiichi Nuclear Power Plant (FDNPP) is proposed. A stereo camera mounted on an inspection system with a rotating base was inserted into the pedestal below the reactor pressure vessel (RPV), and the waterdrops from the leakage position were captured using a stereo camera. We estimated the leakage positions by triangulating the waterdrop trajectory lines in the stereo image. The main contribution of this study is the extraction and matching of the waterdrop trajectories in a stereo image in the FDNPP. The radiation noise is intense inside the pedestal because of the presence of fuel debris. Therefore, we propose a method that is robust against radiation noise. We assume that the waterdrops drip vertically in indoor environments without wind, such as in the FDNPP. Hence, the orientation of the stereo camera can be adjusted by the rotating base such that the vertical lines in the three-dimensional space are also projected as vertical lines in the image planes. Thereafter, the columns of pixels in the images are treated as image features and used to extract and match the waterdrop trajectories. We demonstrated the effectiveness of our leakage position estimation method in a simulated environment of the FDNPP with gamma-ray image noise.
Highlights
The Fukushima Daiichi Nuclear Power Plant (FDNPP) disaster that occurred in 2011 was caused by earthquakes and tsunamis
To the result with three separated waterdrops, the errors were small if waterdrops were not generated near the walls, which indicates the number of waterdrops does not affect the accuracy of the leakage position estimation
We proposed a method for estimating the leakage positions in the pedestal of the FDNPP using a stereo camera
Summary
The Fukushima Daiichi Nuclear Power Plant (FDNPP) disaster that occurred in 2011 was caused by earthquakes and tsunamis. Some fuel debris fell into the pedestal below the RPV, and the rest remained in the RPV. Some inspections conducted in the primary containment vessel (PCV) of Units 1, 2, and 3 of the FDNPP [3,4] revealed that waterdrops were dripping from the bottom of the RPV into the pedestal. Water was injected into the RPV to cool the remaining fuel debris that generated decay heat, and the water leaked from the damage at the bottom of the RPV. Determining the leakage position of the cooling water helped us estimate the location of the damaged area at the bottom of the RPV, which should be beneficial for estimating the rough distribution of the fuel debris in the pedestal because the fuel debris fell through the damage to the bottom of the RPV
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