Gas-cooled fast reactor

Classed as a Generation IV reactor, it features a fast-neutron spectrum and closed fuel cycle for efficient conversion of fertile uranium and management of actinides.

The reference reactor design is a helium-cooled system operating with an outlet temperature of 850 °C (1,560 °F) using a direct Brayton closed-cycle gas turbine for high thermal efficiency.

It differs from the HTGR design in that the core has a higher fissile fuel content as well as a non-fissile, fertile, breeding component.

It must be composed of elements with low neutron capture cross sections to prevent positive void coefficient and induced radioactivity.

The use of gas also removes the possibility of phase transition–induced explosions, such as when the water in a water-cooled reactor (PWR or BWR) flashes to steam upon overheating or depressurization.

The main challenges that have yet to be overcome are in-vessel structural materials, both in-core and out-of-core, that will have to withstand fast-neutron damage and high temperatures (up to 1,600 °C [2,910 °F]).

A European gas cooled fast reactor (GFR) demonstrator, ALLEGRO, is currently being developed by Czech Republic, France, Hungary, Slovakia and Poland.