Firm Energy Accreditation for Small Modular Reactors under El Niño (ENSO) Stress in Hydro-Dominant Power Systems:

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. This paper proposes a replicable, 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, and aggregates these outcomes into annual accredited firm energy (AFE). 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 (i) accredited firm energy is sensitive to the empirical definition of stress months, underscoring the need for data-based climatic conditioning rather than generic ENSO labels; (ii) reduced dependence on freshwater cooling yields systematically higher and more stable accredited outcomes under hydrological stress; and (iii) the methodology produces internally consistent, interpretable results across ENSO episodes, supporting its use as a forward-looking reliability tool. The proposed parameterization protocol and reporting package are designed to be auditable and portable to other hydro-dominant, ENSO-exposed jurisdictions by substituting local stress definitions, derating profiles, and regulatory firmness criteria. Keywords: small modular reactors; firm-energy accreditation; ENSO (El Niño–Southern Oscillation); hydro-dominant power systems