Fuel element having variable orifice

A fuel element for a gas-cooled nuclear reactor having a housing surrounding a plurality of fuel pins through which coolant flows over the fuel pins is described. The housing has a portion of varying cross section and a plug disposed within the housing adjacent the portion. The plug and housing form a generally annular orifice through which the gas coolant flows, the size of which orifice is variable in accordance with the axial position of the plug, which can be varied from exterior of the reactor pressure vessel