Fuel Elements for the Gas-Cooled Fast Reactors

Stainless-steel-clad UOj-PuO fuel elements have been assumed for the reference design of the gas-cooled fast reactor cores, although comparative evaluations of stainless-steel-clad carbide fuel elements have been made 14). In either case, the type of fuel element envisioned for the gas-cooled fast reactors is an assembly of approximately 1-cm-diam, stainless-steel-clad fuel rods. The subdivision of the fuel must be very great in order to achieve the high core power densities and fuel ratings required for reasonable performance with a fast-neutron-spectrum reactor. 

Studies on the gas-cooled, fast-spectrum reactor have shown that a potential advantage of carbide fuel over oxide is derived from its increased conductivity, increased heavy metal density, and decreased moderating effect. The improved conductivity of the carbide over the oxide may allow the maximum heat removal per foot of fuel element to be raised from 20 to about 40 kW/ft. Increased heavy metal density and decreased moderating effect of the carbide allow the possibility of a harder neutron spectrum and therefore an increase of about 10% in the breeding ratio. 

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