The Sodium-cooled Fast Reactor (SFR) is one of the most promising Generation IV systems with many advantages, but has one dominating neutronic drawback – a positive sodium void reactivity. The aim of this study is to develop and apply a methodology, which should help better understand the causes and consequences of the sodium void effect. It focuses not only on the beginning-of-life (BOL) state of the core, but also on the beginning of open and closed equilibrium (BOC and BEC, respectively) fuel cycle conditions. The deeper understanding of the principal phenomena involved may subsequently lead to appropriate optimization studies.Various voiding. Highlights: We analyze the void reactivity effect for three ESFR core fuel cycle states. The void reactivity effect is decomposed by neutron balance method. Novelly, the normalization to the integral flux in the active core is applied. The decomposition is compared with the perturbation theory based results. The mechanism and the differences of the void reactivity effect are explained.
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