We study the impact of fission on the production and destruction of translead nuclei during the $r$-process nucleosynthesis occurring in neutron-star mergers. Abundance patterns and rates of nuclear energy production are obtained for different ejecta conditions using three sets of stellar reaction rates, one of which is based on microscopic and consistent calculations of nuclear masses, fission barriers, and collective inertias. We show that the accumulation of fissioning material during the $r$ process can strongly affect the free neutron abundance after the $r$-process freeze-out. This leads to a significant impact on the abundances of heavy nuclei that undergo $\alpha$ decay or spontaneous fission, affecting the radioactive energy production by the ejecta at timescales relevant for kilonova emission.

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• Fission
• Nuclear astrophysics
• Nuclear matter in neutron stars
• Nucleosynthesis in explosive environments
• r process
• Neutron stars & pulsars
• A ≥ 220
• Nuclear density functional theory