The experimental fast reactor Joyo was constructed as the first step of liquid sodium fast reactor development in Japan, which has been promoted as a government project by the Japan Atomic Energy Agency (JAEA) by incorporating governmental and private sector R&D abilities．
  Joyo has been successfully operated as a breeder core (MK-I core) and an irradiation-test-bed core (MK-II, MK-III core) since its initial criticality, and reached its 30th anniversary on April 24^th, 2007.
  On June 6^th, a celebration of the 30th anniversary of Joyo was held.