Natural uranium consists primarily of U-235 and U-238. When neutrons collide with U-235, it emits huge amounts of energy through a fission reaction, whereas U-238 is less fissile than U-235.
Since natural uranium are contains only approximately 0.7% of U-235, isotope separation (uranium enrichment) is needed to increase its content to 3 to 5% to be used as fuel for light water reactors.
JNFL is the only licensee of uranium enrichment in Japan, and there are plans for the Uranium Enrichment Plant to provide for an ultimate capacity of 1,500 ton-SWU/year, enough to meet about one third of the needs of domestic nuclear power plants.
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.
Feed and Withdrawal Room
Uranium enrichment process
Cascade room where centrifuges, linked with each other, are placed
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. A series of centrifuges —a "Cascade"— is thus linked to produce the necessary level of enrichment.
The maximum enrichment level of uranium 235 at JNFL's Uranium Enrichment Plant is limited to 5%.
Domestic technology developed in Japan
Diagram of a centrifuge
Feeding a gaseous uranium compound, uranium hexafluoride, into a rapidly spinning rotor of a centrifuge separates U-235 and U-238. The heavier isotope, U-238 is pushed outward, while U-235, the lighter isotope, gathers at the center of the rotor. Gas with the higher U-235 concentration is drawn off and sent to another centrifuge. Repeating this process several times produces uranium with increase U-235 content. Using this method, JNFL developed an advanced centrifuge with high efficiency and safety, based on the Japan Atomic Energy Agency’s technology.