Hydrological Drama on the Danube: Bulgaria’s Kozloduy NPP Under Emergency Measures, Coordination with Serbia and Iron Gate to Preserve Safety

Following the shutdown of reactors in Romania (Cernavodă) and power reductions in Hungary (Paks), the extremely low water level of the Danube — the lowest in the last 23 years — has also put Bulgaria’s sole nuclear power plant, Kozloduy NPP, on high alert

Although the two operational 1,000-megawatt units (Unit 5 and Unit 6) remain online and operating according to schedule, the plant’s management has formed a task force and activated emergency measures to ensure uninterrupted cooling.

Collapse of river traffic and the impact on Serbia’s energy system

Furthermore, the crisis on the Danube has escalated into a regional issue affecting multiple energy and transport sectors, with some direct consequences for Serbia:

• Pressure on the Serbian system, Iron Gates and Đerdap: Serbia’s Minister of Mining and Energy, Dubravka Đedović Handanović, stated (on her Instagram account) that she is in constant contact with the Bulgarian Minister of Energy, Iva Petrova. The low water level in Serbia is already hindering the operation of the Iron Gate 1 and Iron Gate 2 hydropower plants, while also putting strain on the cooling systems at the Kostolac Thermal Power Plant.
• Possible assistance from Iron Gate: Bulgarian authorities are considering the possibility of cooperating with Serbia to utilize the technical capacities of the Iron Gate (Đerdap) hydropower complex in order to maintain Danube water levels upstream of Kozloduy above critical operational thresholds.

Technological specifics of Kozloduy: how is this plant defending against the drought?

Regarding Kozloduy NPP — as stressed by the plant itself, which applies to all nuclear facilities — cooling water is used to cool the condensers in the secondary water loops, i.e., the non-nuclear parts of the plant, rather than to cool the nuclear reactors themselves. Kozloduy’s shoreline pumping station was constructed in a deep bay and designed based on century-long hydrological data, currently providing the plant with greater resilience compared to Romania’s Cernavodă. Nevertheless, a prolonged decline in water levels — with the potentially most critical period still ahead in late August and September — threatens to compromise the ability to intake cooling water unless additional flow leveling is secured.

We will follow this situation closely.

S.A.