An Evaluation of the Annular Fuel and Bottle-Shaped Fuel Concepts for Sodium Fast Reactors

Two innovative fuel concepts, the internally and externally cooled annular fuel and the bottle-shaped fuel, were investigated with the goal of increasing the power density and reducing the pressure drop in the sodium-cooled fast reactor, respectively. The concepts were explored for both high- and low-conversion core configurations and for metal and oxide fuels. The annular fuel concept is best suited for low-conversion metal-fueled cores, where it can enable a power uprate of [approximately]20%; the magnitude of the uprate is limited by the fuel-clad chemical interaction temperature constraint during a hypothetical flow blockage of the inner annular channel. The bottle-shaped fuel concept is best suited for tight high-conversion ratio cores, where it can reduce the overall core pressure drop in the fuel channels by >30%, with a corresponding increase in core height between 15 and 18%. A full-plant RELAP5-3D model was created to evaluate the transient performance of the innovative fuel configurations during the unprotected transient overpower and station blackout. The transient analysis confirmed the good thermal-hydraulic performance of the annular and bottle-shaped fuel designs with respect to the reference case with traditional solid fuel pins.