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概要

For safety and early decommissioning of Fukushima, internal survey techniques have been expected to gain an understanding of the state of Fukushima Dai-ichi Nuclear Power Station. Underwater operation and survey is considered to be necessary for vessels and buildings partially filled with retained water. As a complementary of optical instrumentation, ultrasonic underwater visualization techniques have been important for recognizing environment and obstacles for supporting remote operation. In this study, basic specification about underwater visualization was considered in comparison with ultrasonic phased array techniques for non-destructive testing. In the expansion of ultrasonic phased array techniques utilized in the non-destructive testing field, an ultrasonic visualization method combined with sector scanning and divergent beam have been proposed for wide-area shape measurement. Performance of the proposed method was confirmed by visualization experiments for objects in a small-scale environment.

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