The new metal dome encasing Ukraine's infamous Chernobyl nuclear power plant contains enough metal to build three Eiffel Towers with a few thousand tons to spare.
At 108 meters (354 feet) it is taller than the Statue of Liberty and is designed to contain the power plant's dangerous radioactivity while protecting the plant from climactic events for the next century.
The giant dome was fitted 20 years after Chernobyl reactor number four exploded on April 26, 1986, spewing poisonous radiation over large parts of Europe, particularly Ukraine, Belarus and Russia.
The European Bank for Reconstruction and Development (EBRD) is leading the 2.1 billion euro (2.2 billion dollars) project, with contributions from around 40 countries.
The metal dome, built in Italy, rests on a foundation of rectangular concrete beams and weighs 36,000 tons, three and a half times the weight of the iconic Eiffel Tower in Paris.
The 162-metre-long 30-storey high structure now covers an original sarcophagus hurriedly put in place by Soviet workers known as "liquidators", after the worst nuclear accident in history.
Many 'liquidators died'
Over 600,000 "liquidators" were sent to the scene of the accident with little or no protection over four years.
Many died attempting to extinguish the initial fire, isolate the destroyed reactor under concrete and clean up the surrounding area.
The new casing has two objectives: "to contain the radioactive dust and to allow the future dismantling of the damaged reactor as well as the reprocessing of the 200 tons of highly radioactive magma from the old sarcophagus" which has reached the end of its useful life, said the project's director, Nicolas Caille.
Caille, who works for Novarka, the joint venture by French construction firms VINCI and Bouygues which built the dome, hailed it as "a feat of engineering that will ensure optimal safety conditions for the Ukrainian people for the next 100 years."
The structure has equipment and facilities to allow the reactor to be dismantled while limiting the need for human intervention, as the dome will be sealed off hermetically, according to Novarka.
The ventilation system controls the atmosphere inside, regulating the temperature and humidity levels.
The equipment is now due to be tested and completed before a handover to Chernobyl nuclear authorities expected in November 2017.
Designed to withstand earthquakes
The construction of the "New Safe Confinement", as the dome is called, is hailed by organizers as one of the world's most ambitious engineering projects.
Up to 1,220 Ukrainian workers were employed on the site during the "peak period", with a total of 2,500 workers taking part, the teams alternating 15 days on the site and 15 days off to keep exposure to radioactivity "still well below the safety standards set by the nuclear safety authorities," according to the company.
The dome is designed to withstand temperatures ranging from -43 to +45 degrees Celsius and a category 3 storm -- now unlikely in Ukraine, but considered "in case of global warming," Caille told AFP.
And while there is "a low seismic risk" in the country, the structure is also built to resist a strong earthquake, so that even if the concrete sarcophagus were to collapse the metal casing would remain intact.
So far the EBRD has raised 1.5 billion euros from the G7 group of leading economies and international donors. But it is Ukraine which must bear the running costs of the project.
"Much investment will still be needed to bury the radioactive materials that will be recovered," said Olexi Pasyuk of the Ukrainian National Center for Ecology.
