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G-IV: fourth generation reactors

Most all of the present nuclear power plants use thermal neutron induced fission of uranium and plutonium (U-Pu fuel cycle). Fast neutrons produced in fission are slowed down in in water which is also the coolant of the reactor’s core. They are mainly Pressurized Water Reactors (PWR), or Boiling Water Reactors (BWR). They are from the so called second generation of nuclear power plants.

Some reactors of third generation like the EPR are still under construction. They are pressurized water based reactors too, with increasing level of safety.

The concepts for the fourth generation of nuclear reactors have been evaluated regarding five criteria: save natural source (i.e. efficiency of energy extraction from fissile material), lower the proliferation risk, minimize waste production (that includes fuel recycling and minor actinide transmutation), economical sustainability, and last but not least safety.

Six concepts have been selected: they are schematically represented in the following figure:

Sodium fast reactor (SFR), and lead fast reactor (LFR) operate with fast neutrons without a moderator : cooling of the core is made by liquid metal (respectively Na and Pb), as in gaz fast reactor (GFR) the coolant is helium, the very high temperature reactor (VHTR) is also helium cooled, the supercritical water reactor (SCWR) use supercritical water as moderator and coolant, and in the molten salt reactor (MSR) the fuel element is as salt of fissile and fertile elements circulating molten in the coolant. Some of them being already in advanced status like sodium cooled fast neutron reactors, or gas cooled reactors. There is a renewal of interest for molten salt reactors which are good candidates for the thorium based fuel cycle too.

Apart from these six selected concepts, the accelerator driven systems (ADS) dedicated to minor actinide transmutation are also under study.