MK-II Core conversion activities result in the experimental fast reactor "Joyo""

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In the Experimental Fast Reactor "Joyo", Core Conversion from the Breeding Core (MK-I Core) to the Irradiation Core (MK-II Core) was begun in January 1982. Core Conversion required the refueling of 290 core elements, reconstruction of the control rod drive mechanism, and change-out of both the upper guide tube and lower guide tube of the control rods. The schedule for these activities was planned carefully to achieve 100MWt power in March 1983. Joyo achieved MK-II core initial criticality on November 22, 1982, on schedule and immediately began core characterzation. As the result of the Core Conversion activities, we handled many core elements, twice as many as before this core conversion, and in so doing obtained many kinds of experience and data for maintenance and operation of the refueling system. This report describes the considerable pre-conversion activities and planning, and the accomplishments and results of these Core Conversion activities.