Joyo is a sodium-cooled experimental fast reactor fueled by uranium-plutonium mixed oxide (MOX), with operation performance exceeding a quarter century since its first criticality on April 24, 1977. In the first stage of “Joyo,” the core was operated as a breeding core (MK-I core), and the characteristics of the fast reactor core and sodium cooling systems were confirmed by performance tests at a thermal power of 50MW and 75MW as well as at rated-power operations to accumulate technical experience concerning fast reactor plant systems, except the steam generator. The core was then replaced by a new core (MK-II core, thermal power; 100MW), commissioned in 1983, to allow for irradiation tests of fuel and materials.
In addition, in order to more effectively conduct various types of irradiation tests, enlargement of spaces usable for irradiation and an increase in fast neutron flux was achieved in parallel with an increase in the thermal power of the core up to 140MW (MK-III core), and the MK-III core has been operated since July, 2003.Then, the operation will restart at 100 MWt (MK-IV core), which satisfies both the irradiation test performance and the new regulatory requirements.
In addition, Joyo has been providing external users with opportunities for fast neutron irradiation since 1984. |
