Abstract: A nuclear reactor using gas as a primary coolant and a liquid as a moderator and/or reflector. Gas coolant flows through inlet passages around the outlet plenum to a distributor plate. The gas is directed between fuel element housing thimbles and fuel elements therein, through the fuel elements, and into the reactor outlet plenum. Fins on the thimble housings conduct heat to the gas from a liquid moderator circulating in the core. The use of a liquid moderator enhances safety, allows the fissile material and reactor mass to be reduced and eliminates problems associated with cooling of a solid moderator.

Abstract: A gas cooled nuclear fuel element having a particle fuel retention device which acts as a passive restraint in the event of failure of hot frit. A particle fuel retention device is positioned either in the annular space within the inner frit, in the end cap through which coolant gas flows, or attached to the end cap and extending axially beyond the fuel element.