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New York - The Generation IV International Forum (GIF) was created in 2000 to perform research on new types of nuclear reactors to replace the water-cooled models that make up the majority of today's global nuclear fleet.
The group, which consists mainly of public nuclear research agencies, selected the following six systems on which to focus its research efforts.
Sodium-Cooled Fast Reactor (SFR)
- Using superheated liquid sodium as a coolant, this is the most mature technology of the six.
- The metal's low melting point and high boiling point allow the reactor to operate at near-atmospheric pressure.
- Sodium explodes in water and catches fire in air, so research is focused on making the reactors leak-proof.
- Prototypes have been tested in France, Russia and Japan, with China, South Korea and India also proceeding with SFR projects.
Lead-Cooled Fast Reactor (LFR)
- Can operate at atmospheric pressure and high temperatures because of lead's high boiling point of 1 750 degrees Celsius.
- The lead must be kept hot at all times to prevent it from solidifying.
- Lead-bismuth reactors have operated successfully in Russian submarines, but conversion for commercial use requires more research.
- A European consortium is planning to build the "Alfred" LFR demonstration reactor in Romania.
Gas-Cooled Fast Reactor (GFR)
- This will be cooled with helium, which is chemically inert and non-corrosive, but less efficient than liquids at evacuating heat from the core.
- France has been active in GFR development but dropped it in favour of the SFR in 2010.
- Japan and Switzerland have cut back GFR research, but a consortium of the Czech Republic, Hungary, Poland and Slovakia plans to build a small experimental GFR reactor.
Supercritical-Water-Cooled Reactor (SCWR)
- Uses very hot water, above 374 degrees Celsius, as a coolant.
- As with existing boiling-water reactors, steam feeds directly into a steam turbine.
- Unlike some other fourth-generation systems, the SCWR can be developed step by step from current water-cooled reactors.
- Canada leads the way among countries working on this model.
Very-High-Temperature Reactor (VHTR)
- Another evolutionary development of existing models, but with several potential designs, including the pebble-bed reactor.
- The pebble-bed reactor runs gas over spherical fuel elements, has relatively good safety features and the potential for deployment in oil refineries and other industries.
- Among the design challenges is the search for materials that can withstand the extreme temperatures.
Molten-Salt Reactor (MSR)
- Offers two variants: one in which nuclear fuel is dissolved in salt, the other with salt as a coolant.
- The United States conducted MSR research from 1950 to 1976.
- GIF rekindled interest in the concept, but relatively little research has taken place over the past decade.
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