A sill is being built across the Danube to ensure the supply of cooling water to the Paks Nuclear Power Station

Construction of a riverbed sill on the Danube in the vicinity of the Paks Nuclear Power Station is to begin immediately, Péter Magyar announced following the off-site cabinet meeting. The Prime Minister explained that the aim of the project is to ensure that the volume of cooling water required for the power station’s operation can be guaranteed even in the event of persistently low water levels. The decision was taken by the government following a site visit on Thursday, based on the unanimous recommendation of experts in water management, energy and defence.
The structure will be built between the two banks of the Danube, in the area between the Paks Nuclear Power Station and Dunaszentbenedek. In the first phase, around 35,000 cubic metres of rock will be used in its construction, with a total of up to 110,000 cubic metres to be used in subsequent phases. According to the plans, the completed riverbed sill could raise the river’s water level by up to one metre, whilst not hindering the receding of floodwaters in the future.

Reporting on the decisions taken at the government’s meeting held at the Paks Nuclear Power Station, Péter Magyar explained that the water level of the Danube had risen temporarily in recent days, but according to the water management forecast, it could fall back to around minus 136–137 centimetres within 4–5 days. Without external intervention, the water level could fall below minus 140 centimetres next week, which is why the possibility of a complete shutdown of the power station may arise once again, he added. 

A stone embankment is being used to protect the riverbed

The first step in the construction process is to lay a wide layer of stone on the riverbed. This forms the foundation of the structure and prevents the strong current from eroding the riverbed beneath the structure and in its vicinity. The riverbed sill is then built up layer by layer on top of this stone layer. During the works, large stones weighing several tonnes will be placed in the riverbed, with work expected to be carried out from both banks of the river. As the entire construction process takes place underwater, the precise placement of the stones and the continuous monitoring of the structure’s stability present a particularly complex technical challenge.
The Budapest University of Technology and Economics has also been involved in the planning of the project. Every stage of the construction is being carried out in accordance with plans drawn up by water management and nuclear experts.

Tens of thousands of tonnes of rock are being moved

Due to the extremely tight timeframe, work will commence simultaneously at several sites. The extraction and transport of the required quantity of stone to Paks will begin, as will the establishment of work sites and storage areas, and the reinforcement of transport routes where necessary.
Construction will take place 24 hours a day, under temporary site lighting. On the Paks side, the worksite will be established within the nuclear power station grounds, and the project will be organised in such a way as to cause the least possible disruption to life in the surrounding communities.
The construction of the riverbed sill represents a hydraulic engineering project on a scale not seen on the Danube for decades. The last intervention of similar significance on the river took place during the construction of the Dunakiliti riverbed sill, which was completed in 1995.

Two barges are being prepared for the emergency operation

Alongside the construction of the permanent structure, a temporary engineering solution is also being prepared. As part of this, two barges, each approximately 80 metres long, will be transported to the Paks area. Should the water level of the Danube fall to a critically low level before the completion of the riverbed sill, the barges would be turned on their sides, secured and then deliberately sunk. In the short term, this measure could raise the river’s water level by around 20 centimetres. The necessary technical, hydrological and nuclear safety assessments will be carried out before a final decision is made.

The combined cost of the bottom threshold and the temporary measure is estimated at around 6 billion forints.