General outline of the decommissioning of the prototype fast breeder reactor Monju

Kobayashi, Hideharu; Naruse, Keiji; Hirako, Kazuhito; Sawazaki, Hiromasa; Goto, Takehiro; Obata, Ikuhito; Matsui, Kazuaki

The prototype fast breeder reactor MONJU is a loop-type sodium-cooled nuclear reactor to be decommissioned in Japan. Japan Atomic Energy Agency (JAEA) started decommissioning of MONJU in 2018, and will complete four phases of the decommissioning in about 30 years. The first Phase is the Fuel Assembly Removal Period, during which secondary sodium was drained, the fuel assemblies in the reactor core were removed and put in the storage in the spent fuel pool, and the distribution of contamination in buildings, components, equipment, etc. was evaluated. In the second Phase, the Preparation for dismantling period, the neutron shields in the reactor core will be moved and put in the storage in the spent fuel pool in preparation for the dismantling of the sodium equipment, the transport of sodium, and the dismantling and removal of the water and steam power generation system. We also continue to assess the distribution of contamination in buildings, components, equipments, etc. The third Phase is the Decommissioning Period I, which includes the dismantling of sodium equipment, the transport of spent fuel, and the removal of the water and steam power generation equipment. The final Phase is the Decommissioning Period II. The radiation controlled area will be freed and all the buildings will be dismantled and removed. This paper provides an overview of MONJU decommissioning, the results of its First Phase, and details of the second Phase, which is currently underway.