Natural uranium consists primarily of U-235 and U-238. When neutrons collide, U-235 emits huge amounts of energy through fission reaction, while nuclear fission does not occur with U-238. Since natural uranium ore includes only approximately 0.7% U-235, natural ore itself cannot be used in nuclear power generation with a light water reactor. It needs to be enriched to a concentration of 3 to 5%.

      Putting uranium compound gas (uranium hexafluoride) into a centrifuge (cascade) rotating at a high speed separates U-235 and U-238; U-238, a heavier isotope, is pushed outward while U-235, a lighter isotope, gathers inward. Gas with a higher concentration of U-235 is sent to another centrifuge. Repeating this process several times produces usable uranium. This method, developed by the Power Reactor and Nuclear Fuel Development Corporation(PNC), Japan, is one of the most efficient and safe uranium enrichment methods in the world.

      Plans or the Uranium Enrichment Plant provide for an ultimate capacity of 1,500 ton-SWU/year, enough to meet one third of the nuclear fuel needs of nuclear power plants in Japan. Currently, the Uranium Enrichment Plant is operating with a capacity of 1,050 ton-SWU/year, which is equivalent to the nuclear fuel used by 8 or 9 reactors at 1,000 MW-class nuclear plants. Regarding a 450ton-SWU/year capacity, the last half of the 900 ton-SWU/year capacity to be completed in the second phase, a centrifuge with performance 2.5 to 3 times higher than conventional ones will be adopted.

Uranium Enrichment The concentration of U-235, with which nuclear fission occurs, is increased from approximately 0.7% to 3-5%. Enrichment methods include the gaseous diffusion process, the laser enrichment method, and the centrifuge process, which JNFL uses.

U-235 and U-238 Uranium, which is used in nuclear power generation, includes U-235 and U-238. These two isotopes of uranium, almost like twins, differ only in the number of their neutrons. When a U-235 atom absorbs a neutron, it loses stability, which causes nuclear fission. Nuclear power generation utilizes thermal energy emitted at the time of nuclear fission. A U-238 nucleus, on the other hand, does not split when a neutron is absorbed; instead U-238 changes into plutonium 239.

Central Control Room at the Uranium Enrichment Plant	Feed and Withdrawal Room	Homogenization Room

Cascade room where centrifuges, linked with each other, and placed Cascade Since a single centrifuge can only increase the enrichment by a slight degree the process must be repeated by many centrifuges to attain the level of enrichment required for light water reactors. Aseries of centrifuges -a "Cascade"- is thus liked to produce the neccesary level of enrichment.

How a centrifuge works Like a spin dryer, a rotor spins at extremely high speeds in the centrifuge so that UF6 gas is pushed toward the rotor walls by a powerful centrifugal force, thousand times stronger than gravity. At this time, UF6 with a high proportion of heavy U-238, is pushed outward, and UF6 with a high proportion of light U-235 tends to gather around the center. UF6 gas in the center is collected and is processed into enriched uranium.