Uranium Enrichment

About Uranium Enrichment

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 contains only approximately 0.7% of U-235, isotope separation (uranium enrichment) is needed to increase the concentration to 3-5% to be used as fuel for light water reactors.
JNFL has a plan for the Uranium Enrichment Plant to provide for a maximum capacity of 1,500 ton-SWU/year.

Enrichment Process

The concentration of U-235, is increased from approximately 0.7% to 3-5% by uranium enrichment. There are several enrichment methods exists, including the gaseous diffusion, laser enrichment and gas centrifuge technology.
Among these, the gas centrifuge process is currently most widely used, and JNFL employ this technology.

Feed and Withdrawal Room

Homogenization 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

When a gaseous uranium compound and uranium hexafluoride is fed into a rapidly spinning rotor of a centrifuge, U-235 and U-238 gets separated. The heavier isotope, U-238 is pushed outward, while U-235, the lighter isotope, gathers at the center of the rotor. Gas with a higher U-235 concentration is drawn off and sent to another centrifuge. Repeating this process several times produces uranium with increased 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.

Operational Status at Uranium Enrichment Plant

As of August 31, 2026

Current Status

The Rokkasho Uranium Enrichment Plant began commercial operation in 1992 with capacity of 150 tSWU/year. The facility was subsequently expanded by 150 tSWU per year, reaching a total authorized capacity of 1,050 tSWU/year in 1998 (RE-1: 600 tSWU/year; RE-2: 450 tSWU/year).

In 2017, approval was obtained to revise the business plan, including the suspension of the production function of RE-1 (600 tSWU/year). As a result, the plant's current licensed capacity is 450 tSWU per year.

Within RE-2 (450 tSWU/year), the initial 75 tSWU/year capacity was upgraded to new centrifuges through two phases of replacement beginning in March 2010. Production resumed for the first 37.5 tSWU/year in March 2012, followed by the remaining 37.5 tSWU/year in May 2013. However, production was voluntarily suspended from September 2017 to implement safety enhancement measures required under Japan's new regulatory standards.

In August 2023, the plant received the required pre-service inspection certificate from the Nuclear Regulation Authority, confirming compliance with the new regulatory standards, and uranium enrichment operations resumed.

Of the 375 tSWU/year planned for the full-scale introduction of new centrifuges, the first 75 tSWU/year completed replacement, received its pre-service inspection certificate in July 2024, and has now entered commercial production.

For the remaining 300 tSWU/year, approvals for the design and construction plans were granted in August 2024 and May 2025. Work is currently underway to install additional new centrifuges and implement further safety upgrades to meet the new regulatory requirements.

The plant aims to achieve a total enrichment capacity of 1,500 tSWU/year.