Construction and function tests of experimental fast reactor 'JOYO'

Experimental fast reactor ''JOYO'' is the first sodium cooled fast reactor using Pu-U mixed oxide fuel. The construction of the reactor started in March, 1970 and reached initial criticality at 11:07 a.m. on April 24, 1977. The power of ''JOYO'' will reach 50 MWt in the initial power-up test and after further tests going to 75 MWt, the modification of the core is expected. ''JOYO'' will then start working as an irradiation test reactor at 100 MWt. The results of the use of the reactor together with the operational and maintenance experience will contribute to the development of the prototype fast breeder reactor ''MONJU'' and the following breeder reactors of Japan. In this report, the schedule and outline of the construction, technical problems which were met during construction, reconstruction due to design review, results of the function tests and the experience of initial fuel loading to reach initial criticality are given. (auth.)