Plant characteristics evaluation of experimental fast reactor 'Joyo'

The fast breeder experimental reactor 'Joyo', the first liquid metal-cooled FBR in Japan, has completed six cycles of operation at 75 NW rated output in 1981, and in January, 1982, the works to convert from Mark-1 core to Mark-2 core were started. In this paper, the state of operation of Joyo after having attained the criticality in April, 1977, to December, 1981, is reported. In 1977, various tests related to the reactor physics were carried out at 100 kW output at most. The self-initiative check-up was performed after the tests. From April, 1978, the test to raise the power output to allowable 50 MW was started, and in July, 50 MW was attained. Thereafter, from October to February, 1979, two cycles of the rated output operation at 50 MW were performed. One cycle comprises operation for 45 days and stop to replace fuel for 15 days. The first regular inspection was carried out in 1979, during which the test to raise the power output to 75 MW was performed. In July, 1979, 75 MW was attained. Thereafter, three cycles each of the 75 MW operation were carried out in 1980 and 1981. The cumulative time of operation amounted to about 13,000 h, and the maximum burn up was 40,500 MWD/T. The failure of fuel never occurred. The experience of maintenance, the plan of Mark-2 operation, the nuclear design of the core and the actual result of measurement are reported. (Kako, I.)