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TheToshiba 4S (Ultra super safe, Small and Simple) is amicrosodium-cooled nuclear fission reactor design.
The plant design is developed by a partnership that includesToshiba and theCentral Research Institute of Electric Power Industry (CRIEPI) of Japan.[1]
The technical specifications of the 4S reactor are unique in thenuclear industry.[2] The actual reactor would be located in a sealed, cylindrical vault 30 m (98 ft) underground, while the building above ground would be 22×16×11 m (72×52.5×36 ft) in size. This power plant is designed to provide 10megawatts of electrical power with a 50 MW version available in the future.[3]
The 4S is afast neutron sodium reactor. It usesneutron reflector panels around the perimeter to maintainneutron density. These reflector panels replace complicated control rods, yet keep the ability toshut down the nuclear reaction in case of an emergency. Additionally, the Toshiba 4S utilizesliquid sodium as a coolant, allowing the reactor to operate 200 degrees hotter than if it used water.[clarification needed] Although water would readily boil at these temperatures, sodium remains a liquid; the sodium coolant therefore exerts very low pressure on the reactor vessel even at extremely high temperatures.[citation needed]
The Toshiba 4S Nuclear Battery was proposed as the power source for theGalena Nuclear Power Plant in Alaska, but the project was abandoned in 2011 and Toshiba did not proceed with an application for certification of the design.[4]
A research team includingAllison Macfarlane andRodney C. Ewing evaluated waste production of a number of small nuclear reactors, including the 4s, and published their findings inProceedings of the National Academy of Sciences of the United States of America. They found that small modular reactors produce more radioactive waste than conventional reactors. These claims were contested byNuScale Power.[5]