Assessment of Radiological Doses and Emergency Planning Zones of the Rooppur Nuclear Power Plant

Abstract

Bangladesh is introducing nuclear power to meet rising energy demands and reduce reliance on fossil fuels, with the Rooppur Nuclear Power Plant (NPP) commissioning two 1,200 MWe VVER- 1200 units in 2025 and 2026. While routine operations produce minimal radioactive releases, severe accidents, particularly long-term Station Blackout (LTSBO) events, can have significant radiological consequences, highlighting the need for robust emergency preparedness. Despite the use of advanced safety systems of housed VVER-1200 reactor, the adequacy of existing emergency planning zones (EPZ) and response measures at Rooppur NPP requires careful, site-specific evaluation to align with post-Fukushima IAEA safety requirements. Literature reviews point out research gaps, including limited analysis of beyond-design-basis accidents (BDBA), insufficient use of high-resolution atmospheric dispersion models, inadequate consideration of meteorological variability, lack of assessment of trans-boundary impacts, and the need for evidence-based EPZ design. This study introduces several methodological advancements in radiological dose assessment for the Rooppur NPP. It extends previous work by analyzing BDBA, particularly LTSBO scenarios initiated by external events, and by employing plant-specific source terms derived from MELCORbased SOARCA analyses. Radiological doses are evaluated across major exposure pathways while accounting for seasonal, diurnal, spatial variability using long-term (thirty-year), three-dimensional meteorological data and high-resolution atmospheric dispersion modeling. The study further applies post-Fukushima IAEA dosimetric criteria to reassess EPZs, evaluates the effectiveness of sheltering measures, and incorporates uncertainty analysis to ensure conservative and robust dose estimates. It uses modern accident consequence tools like Radiological Assessment System for Consequence Analysis (RASCAL 4.3), HotSpot 3.1.2, and Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) codes both in partial core melt (PCM) and complete core melt (CCM) under IAEA INES level 6 and 7 events. This also investigated the six LTSBO cases, both with and without passive safety systems like the Emergency Core Cooling System (ECCS), different leak rates and water uncovering times. Gaussian plume and puff models were used to simulate transport and dispersion of radioactive material for Monte Carlo randomly sampled yearly 360 possible weather scenarios considering the Rooppur region’s (Ishurdi) meteorological data. Results indicate that inhalation of I-131 dominates exposure near the plant immediately after release, while groundshine from deposited radionuclides, primarily Cs-137, becomes the main source over time. Meteorological conditions strongly affect dispersion: unstable conditions promote rapid dilution and shorter hazard distances, whereas stable conditions allow plumes to travel farther. Wet weather enhances deposition and groundshine, while dry conditions increase inhalation exposure. Deposition patterns peak close to the release point and are significantly higher during wet weather, with short-lived iodine and tellurium isotopes dominating early ground contamination. HotSpot predicts higher doses near the source but decreases faster with distance compared to RASCAL. In PCM scenarios, TEDE reached ~1,000 mSv, while CCM scenarios peaked at 11,000 mSv at 0.5 km, decreasing with smaller leaks or delayed containment failure. Simulations show that in the LTSBO event, sheltering-in-place or evacuation should be taken within 2 to 49 km of the Rooppur NPP reactor site based on criteria of TEDE 10 mSv for level 7, and within 0.7 to 14 km according to criteria of 100 mSv. Prophylactic measures to prevent radioiodine uptake by the thyroid may be necessary within a 3 to over 80 km radius for a threshold thyroid Committed Dose vii Equivalent (CDE) of 50 mSv, depending on weather and accident conditions. The sensitivity results indicate that predicted air concentrations and ground deposition can increase by approximately four to six times when using a finer concentration grid of 0.010° (≈1 km × 1 km) compared to a coarser grid of 0.050° (≈5 km × 5 km), underscoring the strong dependence of results on spatial resolution. Long-range plume dispersion analysis revealed potential trans-boundary impacts; during a dry month of January, the plume moved south and then north, reaching the Bay of Bengal, Myanmar, and beyond, with heavy fallout near Ishurdi. During a wet month of July, the fallout was confined to a zone within 10-12 km, with ground deposition reaching above 1005 Bq/m2, primarily impacting Northwestern Bangladesh and parts of Eastern India in the initial days. For 95% of the simulated weather scenarios, the maximum distance exceeding Precautionary Action Zone (PAZ) dose criteria was found to be approximately 3–4 km when sheltering in large buildings is available, increasing to 8–9 km when only residential houses are considered. Similarly, Urgent Protective Action Planning Zone (UPZ) criteria were exceeded at distances of about 20–25 km with large-building sheltering and 35–40 km with house-only sheltering. To balance public health protection with the practicality of emergency response, a PAZ radius of 5 km and a UPZ radius of 25 km are recommended for the Rooppur site. The analysis shows that taking shelter in large buildings can reduce radiation exposure much more effectively than staying in regular houses. Therefore, building large emergency shelters in nearby communities, especially in densely populated areas like Rooppur, Ishurdi, is recommended to improve public safety. Routine operation doses remain well below regulatory limits (<0.3% of the annual dose limit). Overall, the findings provide risk-informed guidance for emergency preparedness in Bangladesh, emphasizing sheltering, evacuation, iodine prophylaxis, strengthened infrastructure, and cross-border, weather-aware planning to ensure effective accident management and international safety compliance.