A core catcher (eriyik tutucu) is a passive safety system that collects and cools the molten reactor core beneath the reactor vessel in a severe accident and prevents radioactive materials from escaping the containment building. In the VVER-1200 it is installed at the bottom of the reactor pit; at Akkuyu its vessel is about 6 m high and weighs 144–169 tonnes.
What exactly does a core catcher do?
In normal operation, the core is cooled by water inside the reactor pressure vessel. In a very low-probability accident where all cooling capabilities are lost, the fuel could melt and penetrate the vessel. The core catcher is the last barrier designed for this possibility: a cone-shaped steel vessel receives the melt directly below the reactor vessel. Special filler materials inside react with the melt, absorbing part of its heat, preventing the chain reaction from restarting and keeping the melt in a coolable volume. Because the system needs no electricity or operator intervention, it is considered a passive safety system.
This structure is one of the features that distinguish Generation III+ reactors such as the VVER-1200 from earlier generations.
Where is it located and what parts does it consist of?
The core catcher sits at the bottom of the concrete reactor pit at the centre of the reactor building, beneath the reactor vessel. According to Akkuyu Nuclear (Akkuyu Nükleer), the system consists of three main parts:
- Body (vessel): The cone-shaped steel vessel that holds the melt. It works together with the filler material.
- Cantilever truss (konsol kiriş): Located above the body; it protects the body and measurement lines, provides passage for water supply, steam relief and ventilation lines, and contains inspection corridors.
- Guide plate: The upper section that directs the melt into the body.
Dimensions of the core catchers at Akkuyu
| Unit | Part | Dimensions and weight | Date |
|---|---|---|---|
| Unit 1 | Body | 150 tonnes; the second cargo to arrive at the Eastern Cargo Terminal | On site July 2019 |
| Unit 2 | Body | 5.8 m × 6.1 m, 169 tonnes; 668 tonnes in total with internal equipment | On site August 2020, installed December 2020 |
| Unit 3 | Body | 6.14 m high, 5.83 m diameter, 144 tonnes | June 2022 |
| Unit 4 | Body | 6.14 m high, 5.83 m diameter, 144 tonnes | October 2023 |
| Unit 4 | Cantilever truss | 9.5 m diameter, 2.3 m high, 166 tonnes, six parts | March 2024 |
The bodies were manufactured at the TYAZHMASH plant in Syzran, Russia. In Unit 3, the core catcher was the first major piece of equipment placed in the reactor building.
When and how is it installed?
The installation sequence cannot be changed, because once the body is in place the surrounding reactor pit is concreted and the vessel can no longer be lowered there any other way. The sequence followed at Akkuyu Unit 2 is as follows:
- The body is lowered into its design position, and its position at the bottom of the pit is verified by precise measurement.
- Filler material (cassettes) is placed in the body.
- The reactor pit is built up and concreted around the body.
- The cantilever truss and guide plate are installed, followed by pit components such as the dry shielding and support truss.
Lifting is carried out from above with a heavy crawler crane before the building dome is closed. According to a 2019 statement by Akkuyu Nuclear, a Liebherr LR 13000 crawler crane was erected on site for the Unit 1 core catcher. The method is described in the heavy lifting at nuclear power plants entry.
What are its transport characteristics?
A body of about 6 m in diameter is more than twice the width of the road loading gauge, so it is brought from the manufacturer to the site by sea, directly to the plant's jetty. At Akkuyu, the Unit 3 body was unloaded from the ship at the Eastern Cargo Terminal, moved by on-site road to the unit area and then placed in its design position in the pit. As it is a very wide but relatively light load, the decisive factors are dimensions, lifting points and tipping stability rather than weight. On arrival, a mandatory incoming inspection is carried out with representatives of the manufacturer and Akkuyu Nuclear (see incoming material inspection). As the core catcher is equipment of a high safety class, traceability documents are also delivered with the cargo.
How does Voltim Global support this?
The core catcher itself arrives by sea transport organised by the manufacturer. Voltim Global's experience in nuclear project logistics is based on the Russia–Akkuyu route: more than 450 shipments have been made on this route since March 2024.