Paks II.: What does the new milestone for Unit 5 mean in the context of the review?

The Paks II. project has reached another significant milestone. Construction of the foundation slab for the Unit 5 reactor building has begun – announced on 31 July by Paks II. Zrt.. This phase of the work is considered to be of particular importance because the foundation slab of the reactor building will support one of the most important structural units of the entire nuclear facility.

According to the developer, the construction of the foundation slab is taking place in several phases, subject to extremely stringent nuclear quality assurance standards. The works are being co-ordinated with the foundation works for the other buildings on the shared foundation slab.

In the case of such structures, concrete work is not a simple construction task. The structure must withstand significant static, thermal and dynamic loads for decades.

The heart of the nuclear power station begins underground

The first segment of the base slab is a circular concrete block – a concrete ring – over 50 metres in diameter, 13 metres thick and nearly 3 metres high. Due to its size, it cannot be constructed in one piece; construction is therefore being carried out in several sections along the circular arc. The concreting of the first of these circular segments began on the evening of 30 July 2026. Prior to this, 270 tonnes of reinforcing steel had been installed over a period of two months. From Thursday evening, machinery and specialists worked for twelve hours in the excavation pit and at the concrete plant; over the course of 12 hours, 776 cubic metres of basalt concrete mix with a strength class of C35/45 were poured.

The installation and preparatory work for the first casting phase had been completed beforehand. The receiving levels had been constructed, and the steelwork had been carried out on them. Over the past few months, the so-called embedded and concealed elements – namely stainless steel pipework, geodetic survey points and steel support elements – have been installed. These provide the mounting surfaces for future equipment, pipework and other components.

Meanwhile, the project is undergoing a full review

At the same time, however, this technical progress is taking place at a time when the government that took office in 2026 has subjected the entire Paks II. project to a comprehensive review.

The review in question is not a nuclear safety inspection, but an economic, financial, legal and strategic assessment. Its aim is to determine whether the project, in its current form, serves Hungary’s long-term interests, and whether any contractual or financial adjustments are required.

Paks II. Zrt., however, emphasises that, whilst ensuring business continuity, work is continuing on those projects for which all necessary regulatory approvals have been obtained. This includes the foundation slab works that have now commenced.