A Core Design Study on the Fuel Displacement Options for an Effective Transition between Breakeven and TRU Burning Sodium-Cooled Fast Reactors

Abstract

A core design study to convert a breakeven core into a transuranic (TRU) burner is performed for a 600-MW(electric)–rated metal-fueled sodium-cooled fast reactor. No change in the core and subassembly layouts is assumed, which only allows geometry variations within the fuel rods. Investigated alternatives are to use variable cladding thicknesses (VCTs), smearing fraction (SF) adjustments, and annular fuel rod concepts with a central liner of a variable diameter consisting of void, Zr, B4C, Al, etc.The VCT concept could not be employed due to a too-high clad inner wall temperature. A SF adjustment below a typical fraction of 75% leads to moderate TRU burning and a reduced sodium void worth but also to a relatively high burnup swing. Placing a central nonfuel rod with the fuel arranged in an annular ring affects the core performance and reactivity coefficients, depending on whether it is a moderator or an absorber. In general, candidate materials of high atomic numbers contribute to large positive sodium void worths but also enhanced negative expansion effects. Among the light elements, vanadium reveals a favorable performance with comparable TRU burning and a reduced sodium void worth, suggesting this material can be regarded as a substitute for sodium in the solid state.