To survey core internals simply, new microscopic observation techniques were developed. These techniques were involved the use of “Gel electrode” and “underwater microscope”. A Gel electrode can etch the surface of core internals without a watertight reservoir that makes an etching environment. The underwater microscope can be used to observe surface figures of core internals directly. These techniques were applied to the cracks detected at the shroud support of Tokai II Power Station for investigation of the cause of crack initiation. It became clear that initiation points of the detected cracks were in a nickel-base weld metal.

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