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Chernobyl NSC containment arch moved into place in historic engineering feat

29 November 2016

Reactor number 4 at the Chernobyl nuclear power plant, the scene of the worst nuclear accident in history, has been enclosed by a vast steel shelter designed to prevent radiation leaks from the site. The process of sliding the arched structure into place to shield the damaged reactor started on November 14 and took over a week to complete.

The NSC containment arch in place over Chernobyl Reactor 4 - Image: EBRD
The NSC containment arch in place over Chernobyl Reactor 4 - Image: EBRD

A ceremony at the site was held on November 29, attended by the Ukrainian president, Petro Poroshenko, diplomats and site workers, to celebrate the successful positioning of the containment arch over the stricken reactor.

The so-called New Safe Confinement (NSC) is the largest moveable land-based structure ever built with a span of 257m, a length of 162m, a height of 108m, a total weight of 36,000 tonnes and a cost of more than €1.5bn.

The London-based European Bank for Reconstruction and Development (EBRD), which is part-funding and managing the project, described this milestone at the plant in Ukraine as "one of the most ambitious projects in the history of engineering".

The NSC, assembled in a clean area near reactor 4 shielded from radiation, was pushed along rails over 327 metres to its final resting place with the help of 224 hydraulic jacks pushing the arch 60 centimetres at a time. The structure now covers the reactor and the unstable sarcophagus hastily built by Soviet authorities in the immediate aftermath of the disaster 30 years ago.

Ostap Semerak, Ukraine's minister of ecology and natural resources, said today's event is "the beginning of the end of a 30-year long fight with the consequences of the 1986 accident".

Vince Novak, EBRD's nuclear safety director, said the NSC project would not have been possible without the support of the over 40 donor countries who are contributors to the Chernobyl Shelter Fund. He said: "The new structure illustrates what is possible in a spirit of determined and coordinated joint effort and thanks to the generous support of EBRD shareholders."

He said the shelter eliminated a number of fears and risks that had persisted since the accident, including a collapse of the sarcophagus or a fresh nuclear reaction inside the structure, given the tonnes of uranium still present at the site. There was also a danger that radioactive liquids could seep out of the site and into the water supply, because the sarcophagus was not watertight, he said.

The construction of the NSC by Novarka - a French construction consortium formed by VINCI Grands Projets and Bouygues Construction - started in 2012. Because of its vast dimensions the structure had to be built in two halves which were lifted and successfully joined together in 2015. The arch-shaped structure is fitted with an overhead crane to allow for the future dismantling of the existing sarcophagus and the remains of reactor 4.

Prior to the process, tens of thousands of tonnes of radioactive soil were removed from the construction area and replaced with clean soil. Much of the machinery and engineering equipment used had to be designed and built from scratch, including special cladding and a huge crane system.

On 26 April 1986, the Chernobyl plant suffered the worst nuclear accident in history when a power runaway event wrecked reactor 4. The three remaining reactor units, however, were vital to Ukraine's electricity needs and continued to operate for some years. Unit 2 shut down in 1991, unit 1 in 1996 and unit 3 in 2000. The plant officially entered the decommissioning phase in April last year.

The Chernobyl workers who built the initial sarcophagus to cover the damaged reactor were exposed to very high levels of radiation and many died soon after. At the ceremony, President Poroshenko paid tribute to them and their self-sacrifice which helped protect the other citizens of Ukraine.

Over the coming year, work will continue on the structure to make it airtight and dismantle parts of the sarcophagus inside, using remote-controlled cranes inside the structure. When it is completed in November 2017, the final structure should ensure that the site is airtight for 100 years.

Human habitation in the zone around Chernobyl is forbidden and access is only granted by special permit, but a few residents have returned in defiance of the ban. There are plans to develop solar power facilities in the area and Ukrainian authorities want to rebrand the exclusion zone as a destination for tourists.

The nearly 50,000 residents of Pripyat, a town built to house Chernobyl workers, were evacuated the day after the disaster and never returned. Its eerie, deserted streets give a snapshot of the late Soviet period.

Click on the link below to see a timelapse video of the NSC being moved into place.

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