Cooling Technology Selection for Coastal Nuclear Power Plants in Shallow Semi-Enclosed Seas: Study Analysis for the Southern Baltic Sea

The planned Lubiatowo–Kopalino nuclear power plant (NPP) on the Polish Baltic coast requires a cooling technology that balances energy security, economic efficiency, and compliance with a multi-layered framework governing thermal discharge in a sensitive sea. This article integrates regulatory analysis across four instruments (EU Water Framework Directive, Polish discharge standards, HELCOM Baltic guidelines, and IAEA practice) with site-specific evidence from a 2D advection-diffusion thermal plume model. Four cooling options (once-through seawater, closed-loop towers, dry-air, and hybrid) are evaluated against regulatory criteria and against the documented vulnerabilities of the southern Baltic: eutrophication, restricted flushing, and ongoing warming. The modelling indicates that the acute thermal plume (ΔT ≥ 2 °C) remains limited to approximately 1.18 km2 even under summer 90th-percentile conditions, whereas low-magnitude warming (ΔT = 0.1–0.5 °C) extends over approximately 1886.6 km2. Although the once-through system with a multi-port diffuser satisfies current regulatory criteria, the extensive far-field anomaly represents an additional ecological stressor for an already eutrophic and warming marine ecosystem. A staged hybrid approach, with the first unit on validated once-through cooling and subsequent units on hybrid dry/wet systems, emerges as the most sustainable pathway, balancing empirical learning, regulatory foresight, and long-term climate resilience. The analysis offers a transferable framework for thermal-discharge assessment in shallow, microtidal, nutrient-enriched coastal seas, while demonstrating consistency with established regulatory practice and published knowledge on thermal-plume behaviour.