Experimental fast reactor "JOYO" operation report; Operation results of primary overflow system

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The primary overflow system of Experimental Fast Reactor "JOYO" was operated for about 55,000 hours from the in-sodium functional test in February 1976, to the end of 4 the cycle operation at 100 MWt in August 1984. During the period, the overflow system was operated satisfactorily for the purpose. In the beginning of the period, however, it was found that a thermal transient condition exceeds a design limit at overflow return pipe while a process to recover the system after the loss of electric power. In order to prevent unnecessary thermal transient, operation procedure and test results were studied and new operation procedure was established. Although the new procedure satisfies the required conditions, it takes 10 to 16 hours to recover the plant in case of loss of electric power. Therefore, for the efficiency of plant operability, the study should be continued.