Fast Breeder Reactors

Fuel – 239Pu bred from 238U in the reactor using neutron capture
Cladding – stainless steel
Moderator – none
Coolant – liquid metal such as sodium or sodium-potassium alloy due to minimal neutron moderation
Control – boron carbide rods
Shield – originally steel but later reinforced concrete

Breeder reactors rely on the 238U capturing neutrons to create 239Pu which fissions sufficiently with fast neutrons to sustain criticality. 25% more fission neutrons are released than with uranium so placing a blanket of 238U around the reactor would also enable the reactor to breed more 239Pu. If the blanket is not present then the reactor can be used to burn plutonium.

UK Fast Breeder Reactors

Dounreay Fast Reactor, 14 MW, connected in 1962, shut down in 1977

Dounreay Prototype Fast Reactor, 250 MW, connected in 1975, shut down in 1994