Effect of void propagation to sodium void reactivity in transient analyses of fast reactors with sodium-plenum

•The effect of void propagation to sodium void reactivity is analyzed.•A fast reactor core with sodium-plenum is considered.•Void reactivity for sub-region in sodium-plenum is calculated.•Results for two cases with and without considering void propagation are compared.•The results differ by up to twice depending on location of sub-regions.