Once such fuels as petroleum and natural gas are burned, it can no longer be used. In contrast, uranium fuel continues burning for three to four years and can be used repeatedly through reprocessing. In the light-water reactors used in many nuclear power plants, energy is primarily obtained from U-235, whereas, when U-238 absorbs neutrons, part of it changes into plutonium.
The plutonium and residual unburned U-235 is extracted by reprocessing for reuse as raw materials for uranium fuel or Mixed Oxide (MOX) fuel.
This reprocessing is done at the reprocessing plant. Thus, the reprocessing plant may be considered to be "a site where semi-national energy resources are generated". Using reprocessed uranium and plutonium in a light-water reactor allows for 10% to 20% uranium-resource-saving effects. Moreover, in the future, if plutonium were to be used in the Fast-Breeder Reactor that excels in conversion efficiency, utilization efficiency can be expected to improve significantly.
The Rokkasho Reprocessing Plant is the first commercial reprocessing plant in Japan.
As Japan has been "promoting research, development, and the benefits of nuclear energy strictly for peaceful use" ("Nuclear Energy Policy", Japan Atomic Energy Commission), the reprocessing plant employs highly proliferation-resistant technology (uranium-plutonium co-denitration).
In the Rokkasho Reprocessing Plant, buildings are located separately according to process and are interconnected by underground tunnels. Liquid solution is transferred to the next process through piping inside the tunnels.
The maximum reprocessing capacity of the plant is 800 ton-U/year, enough to reprocess the spent fuel produced from about 40 reactors at 1,000 MW-class nuclear power plants.
The operations are managed and monitored in the central control room. The room consists of a monitor-and control board comprising six blocks and a mainframe computer, implementing digital control for processing vast amounts of data efficiently.