New Safe Confinement is a steel arch over the ruined fourth reactor at the Chernobyl nuclear plant.
It is the largest movable structure ever built on land.
Its span is 843 feet (257 meters).
Radiation above the old 1986 concrete sarcophagus was too high for long work on top.
So the arch was not assembled in place.
Engineers from a consortium of French construction firms built it 1,073 feet (327 meters) away from the reactor, on rails.
Workers stayed farther from the most dangerous zone.
On November 29, 2016, the entire structure was slid over the wreckage.
In 2019, the shelter was fully commissioned.
Just a roof?
The arch contains radioactive dust and opens a path to dismantling the aging shelter and managing the waste.
Its design life is 100 years.
And 36,000 metric tonnes?
That is the mass of about 24,000 cars. This load does not travel by road.
It slides on rails above a reactor.
The old sarcophagus was temporary.
The new one is built to last a century.
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