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概要

A thimble tube (hereinafter “thimble“) is a tube through which a cable equipped with a small movable detector (MD cable) is inserted into a nuclear reactor in operation to measure the neutron flux distribution therein. The thimble is a long, small-diameter stainless steel tube with an outer diameter of about 8 mm, an inner diameter of about 5 mm and a length of as long as 36 m. The MD cable that is routed through the thimble is an insertion cable with a spiral wire wound around it, and various types of sensor can be attached to the end thereof to conduct neuron flux measurements or eddy current testing (ECT). In our latest project, a new insertion cable was developed independently and examined for its applicability to practical utilization by an endurance test. In addition, a signal extraction technique, which uses a micro-camera or temperature sensor attached to the end of the cable to grasp the conditions in a nuclear reactor remotely, was developed.

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