ALLEGRO is an experimental fast reactor cooled with Helium being developed by the European V4G4 Consortium “V4G4 Centre of Excellence” of the nuclear research organizations of the Czech Republic, Hungary, Poland and Slovakia associated with CEA, France. Development of ALLEGRO is an important step on the way to the Gas-cooled Fast Reactor, one of the six concepts selected by the Generation IV International Forum and one of the three fast reactors supported by the European Sustainable Nuclear Energy Technology Platform.

The main purposes of ALLEGRO is the development of:

  • GFR refractory fuels (UPuC SiC-SifC cladding)
  • Helium related technologies (components, instrumentation, purification,…)
  • Safety technical issues and corresponding safety approach framework.


ALLEGRO main design characteristics

Nominal Power (thermal) 75 MW Reduced power is being considered in the range

30 – 75 MW.

Nominal Power (electrical) 0 MW
Power density 100 MW/m3 Reduced power density is being considered in the range

50 – 75 MW/m3.

Fuel MOX/

SS cladding

Start-up core.

Feasibility of LEU UOX for the start-up core is being investigated.


SiCSifC cladding

Long term core.
Type of fuel assembly Hexagonal wrapper and wired fuel rods
Number of fuel rods per assembly 169
Number of fuel assemblies 81
Number of experimental fuel assemblies 6
Number of control and shutdown rods 10
Primary circuit coolant Helium
Secondary circuit coolant Water Gas is being investigated
Tertiary circuit coolant Air Atmosphere
Primary pressure 70 bar
Core inlet/outlet temperatures 260/516 °C Should be upgraded for full core refractory fuel.
Number of primary loops 2
Number of secondary loops 2
Number of DHR loops 3 Directly connected to the primary vessel
DHR circuits coolant Helium
DHR intermediate circuits coolant Water
DHR heat sink Water pool
Number of accumulators 3 Filled with Nitrogen