Simultaneous visualization of flow behavior and object shape by pulse ultrasonic for 1F investigation

An ultrasonic measurement system was developed as a method for inspecting inside the primary containment vessel of Fukushima-Daiichi nuclear power plant, especially for identifying leakage points and determining fuel debris distribution. The measurement system has a liner array sensor and enables the obtaining of a 2-D flow map and an object shape at once using ultrasonic velocity profiler (UVP) method and aperture synthesis method respectively. However, the UVP method has a limitation on the detectable velocity range. Then, it is difficult to obtain lower and higher velocities simultaneously. Thus, we developed the velocity limit extension algorithm for the UVP method and the algorithm was embedded in the measurement system. The validity of the developed system for the inspection was investigated experimentally. As a result, the location of a simulated leakage point and shape of mock fuel debris were estimated from the 2-D flow map and reconstructed image using the system. (author)