Firm energy accreditation for small modular reactors under El Niño (ENSO) stress in hydro-dominant power systems: evidence and policy lessons from Latin America

Introduction Hydro-dominant power systems in Latin America are recurrently exposed to ENSO-driven hydrological scarcity, creating adequacy risks precisely when firm energy is most valuable. Methods This paper proposes a Monte Carlo-based methodology to accredit nuclear firm energy for small modular reactors (SMRs) under climatic stress, using an explicit stress-month definition derived from long-run hydrological energy contributions and technology-specific derating profiles. The framework combines planned maintenance, forced-outage processes, and ENSO-conditioned deratings to generate monthly dependable energy at a policy-defined firmness quantile, which is then aggregated into annual accredited firm energy (AFE). Results A worked policy application is presented using two ENSO episodes (2015–2016 and 2023–2024) and three SMR climate-exposure groups: freshwater-cooled, seawater-cooled, and non-water-cooled configurations. Results show that accredited firm energy is sensitive to the empirical definition of stress months, that reduced dependence on freshwater cooling yields systematically higher and more stable accredited outcomes under hydrological stress, and that the methodology produces internally consistent and interpretable results across ENSO episodes. Discussion The proposed parameterization protocol and reporting package are designed to support structured application across hydro-dominant, ENSO-exposed jurisdictions by substituting local stress definitions, derating profiles, and regulatory firmness criteria.