In addition to using uranium fuel, for which research was carried out at the Fugen Power Plant by the Japan Nuclear Cycle Development Institute (currently known as the Japan Atomic Energy Agency, a national research and development agency), the main feature of advanced thermal reactors (ATR) is that they are also capable of using plutonium-uranium mixed oxide (MOX) fuel. The operations of the Fugen Power Plant were terminated in March 2003, and it is currently known as the FUGEN Decommissioning Engineering Center, where the decommissioning of nuclear reactors is being researched and developed by the Japan Atomic Energy Agency, a national research and development agency.

 Advanced thermal reactors use heavy water as a moderator and light water (normal water) as a coolant. Pressure tubes containing fuel are lined up within the calandria tank. The heat from nuclear fission heats the cooling water (light water) in the pressure tubes, which is then turned into steam by the steam drum. This steam is then used to turn the turbine generator and produce electricity.
 Heavy water, which absorbs few neutrons, is used as the moderator to ensure that the neutrons are used as efficiently as possible. The main feature of these reactors is that low-enriched uranium can also be used to generate electricity.