More than 30 years since the Chernobyl disaster contaminated huge swathes of Europe with radioactive material, engineers have finally managed to seal the carcass of the nuclear plant’s destroyed reactor block
The catastrophic chain of events that led to the explosion and fire at the Chernobyl Nuclear Power Plant’s No. 4 reactor in April 1986 is one that will continue to haunt the world community for some time.
Estimates claim that it could be thousands of years before the area immediately surrounding the site in Ukraine is safe for normal human habitation.
In the weeks and months following the disaster, work to contain radioactive emissions saw the doomed reactor buildings covered in tonnes of concrete, creating a ‘sarcophagus’ that has secured the site for the last 30 years.
New Safe Confinement
But this was only ever expected to be a temporary measure, and ever since teams have been working on the design and construction of a New Safe Confinement (NSC) structure, that will envelop the sarcophagus and reactor building.
That vision has seen some of Europe’s finest engineering brains deliver a huge steel-framed cocoon that completely covers the ageing sarcophagus, sealing it from the outside world, preventing any further contamination and enabling clean-up and decommissioning work to progress at a future date within its confines.
Novarka, a 50/50 joint venture between construction giants Vinci Construction and Bouygues Travaux Public, has had the task of building the enormous protective covering. It has been financed through donations from the main G8 countries, European Union member states, as well as organisations including the European Bank for Reconstruction and Development.
“The structure needed to be stable against wind suction forces of class three tornadoes and category seven earthquakes”
A mighty span
Constructed in two halves and rolled into position over the reactor building using a jacking system, the completed NSC structure spans 257m with a height of 105m and length of 150m.
Developed by specialist cladding provider Kalzip, the covering itself consists of an arched latticed steel framework with an airtight outer layer clad using standing seam steel roofing systems. The inner layer is similarly airtight and clad with stainless steel sheets fixed to the frame.
The steel frame is prefabricated in sections offsite, including temperature control services and crane runs, before being jacked into position in stages where the cladding skins are installed; there is a gap of around 13m between these two cladding skins. This annular gap has been positively pressurised, while the main volume of the steel structure surrounding the reactor building is kept under a slightly negative pressure. This pressure differential ensures there is no radioactive leakage from the NSC but also helps stabilise the 30,000-tonne structure.
Fit for task
“The structure needed to be stable against wind suction forces of class three tornadoes, and category seven earthquakes. This was a challenge for our engineers,” admits Kalzip managing director Jörg Schwall. He adds: “But test results showed that the outer and inner shells developed specifically for this application – and that standing seam systems – could exceed these requirements by 70 percent.”
The resulting steel-framed structure has a design life of 100 years with minimal maintenance and will provide resistance to fire, wind and snow loading, contain the radioactive dust and provide a capacity for the eventual decontamination of the Chernobyl site.