The energy transition requires balancing the three dimensions of the Energy Trilemma: decarbonization, affordability, and security of supply. In this context, Small Modular Reactors (SMRs) have emerged as a promising low-carbon technology, although their role in long-term energy planning analyses remains insufficiently explored.This study assesses the potential contribution of SMRs to the Italian energy system using an energy system optimization model (ESOM) with a sector-coupling approach integrating electricity, heat, and hydrogen. SMRs are modelled as flexible cogeneration technologies coupled with thermal energy storage, enabling the joint supply of electricity and process heat. Four policy-driven scenarios are compared against a baseline scenario, consistent with the Italian National Energy and Climate Plan (PNIEC) targets, and results are evaluated via a structured set of indicators aligned with the Energy Trilemma - the Decision Scoreboard.Results show that, while achieving comparable decarbonization levels by 2050, scenarios significantly differ across the other Trilemma dimensions. Nuclear scenarios reduce reliance on solar photovoltaic and battery capacity, limit renewable curtailment, and enhance energy mix diversification. When deploying the entire nuclear fleet in cogeneration mode, SMRs further reduces heat-sector CO2 intensity by 50% compared to the baseline, while lowering system costs and natural gas penetration. However, nuclear deployment introduces dependence on imported uranium fuel, which requires dedicated supply chain diversification strategies to genuinely strengthen energy security.These findings emphasize the importance of sector-coupling approaches to fully capture the value of multi-product technologies such as SMRs, and inform evidence-based policymaking on nuclear integration in low-carbon energy systems.