Assessment of the Impact of Thermal and Chemical Loading on the Koporye Bay of the Gulf of Finland with the Full Commissioning of the Leningrad Nuclear Power Plant-2

Abstract The study evaluates the thermal and chemical impact of nuclear power plants with VVER (water-water energetic reactor) and RBMK (uranium-graphite channel type reactor) reactors on the cooling pond, using Leningrad NPP (LNPP) in Koporye Bay (Gulf of Finland, Baltic Sea) as an example. A three-dimensional hydrodynamic model of the eastern Gulf of Finland was developed to assess heat and chemical discharge effects. Calculations were performed for two scenarios: 1) simultaneous operation of LNPP-1 (RBMK) and LNPP-2 (VVER); 2) operation of LNPP-2 only. The year 2010 was selected as it exhibited extreme environmental conditions in the bay. In the "LNPP-1 and LNPP-2" scenario, temperatures at discharge points remained within regulatory limits. The thermal plume extended up to 3 km with a maximum temperature excess of 10°C. Relative tracer concentrations ranged from 10–80% near the main discharge and 9–31% at the secondary discharge point. The "LNPP-2 only" scenario showed no significant temperature disturbances or ice cover changes. Tracer concentrations near the discharge did not exceed 6% of source levels. Both scenarios demonstrated that temperature and pollutant concentration changes remained within established standards. The transition from RBMK to VVER reactors at LNPP would significantly reduce thermal and chemical impacts on Koporye Bay.