Simplified thermal expansion modeling for liquid metal-cooled fast reactors

While high resolution thermal expansion modeling in Liquid Metal-cooled Fast Reactors (LMFRs) is becoming more common, such models typically require supercomputers and hundreds of compute-hours. Practical reactor design calculations require simplified models and, therefore, more simplified thermal expansion modeling. In this paper, 3 thermal expansion models of varying complexity are compared using the computer program LUPINE: LMFR Utility for Physics Informed Nuclear Engineering. These 3 models are compared by modeling the Advanced Burner Reactor (ABR) benchmark with metallic fuel and a typical Lead-cooled Fast Reactor (LFR) with nitride fuel. It is observed that even the simplest thermal expansion model captures most of the reactivity effects of thermal expansion. The results demonstrate that all models perform acceptably and the sensitivity of k_eff to thermal expansion is largely determined by the reactor fuel type. Local power changes due to thermal expansion are also compared. It is determined that a model using spatially dependent thermal expansion in the axial direction is preferred as it incorporates the most geometric information and captures both reactivity and power distribution effects of thermal expansion. (authors)