Sodium-cooled fast reactor
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The Sodium-cooled fast reactor or SFR is a Generation IV reactor project to design an advanced fast neutron reactor.
It builds on two closely related existing projects, the LMFBR and the Integral Fast Reactor, with the objective of producing a fast-spectrum, sodium-cooled reactor and a closed fuel cycle for efficient management of actinides and conversion of fertile uranium.
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[edit] Fuel Cycle
The fuel cycle employs a full actinide recycle with two major options: One is an intermediate size (150 to 600 MWe) sodium-cooled reactor with uranium-plutonium-minor-actinide-zirconium metal alloy fuel, supported by a fuel cycle based on pyrometallurgical reprocessing in facilities integrated with the reactor. The second is a medium to large (500 to 1,500 MWe) sodium-cooled reactor with mixed uranium-plutonium oxide fuel, supported by a fuel cycle based upon advanced aqueous processing at a central location serving a number of reactors. The outlet temperature is approximately 510-550 degrees Celsius for both.
[edit] Sodium as a Coolant
Water cannot be used as a coolant for a fast reactor because water acts as a neutron moderator that slows the fast neutrons into thermal neutrons. Sodium is much less likely to interact with the neutrons being emitted from the chain reaction. However, the fast neutrons are more likely to interact with isotopes that do not contribute to a chain reaction, so the fuel has to be more highly enriched than the light water reactor fuel.
[edit] Design Goals
The operating temperature should not exceed the melting temperature of the fuel. It has been found that the melting point of a fuel called SFR-MOX (20% tranuranic oxides and 80% uranium oxide). Fuel-to-cladding chemical interaction (FCCI) has to be designed against. FCCI is eutectic melting between the fuel and the cladding; uranium, plutonium, and lanthanum (a fission product) inter-diffuse with the iron of the cladding. The alloy that forms has a low eutectic melting temperature. FCCI causes the cladding to reduce in strength and could eventually rupture. The amount of tranuranic transmutation is limited by the production of plutonium from uranium. A design work-around has been proposed to have an inert matrix. Magnesium oxide has been proposed as the inert matrix. Magnesium oxide has an entire order of magnitude smaller probability or interacting with neutrons (thermal and fast) than the elements like iron. [1]
The SFR is designed for management of high-level wastes and, in particular, management of plutonium and other actinides. Important safety features of the system include a long thermal response time, a large margin to coolant boiling, a primary system that operates near atmospheric pressure, and intermediate sodium system between the radioactive sodium in the primary system and the water and steam in the power plant. With innovations to reduce capital cost, such as making a modular design, removing a primary loop, integrating the pump and intermediate heat exchanger, or simply find better materials for construction, the SFR can be a viable technology for electricity generation. [2]
The SFR's fast spectrum also makes it possible to use available fissile and fertile materials (including depleted uranium) considerably more efficiently than thermal spectrum reactors with once-through fuel cycles.
[edit] References
[edit] See also
- Fast breeder reactor
- Fast neutron reactor
- Integral Fast Reactor
- Lead-cooled fast reactor
- Gas-cooled fast reactor
- Generation IV reactor
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