A huge shelter has finally been installed over the exploded reactor at the Chernobyl nuclear plant, signalling the end of one of the most ambitious engineering projects in the world.

The New Safe Confinement (NSC) shelter is a half-cylinder shaped structure which started being moved towards the reactor two weeks ago, finally reaching its destination on Tuesday.

The move is a significant step towards demolishing unstable parts of the old cover - the so-called sarcophagus - and parts of the damaged reactor.

After the Chernobyl disaster in 1986 - the world's worst nuclear accident - the sarcophagus was hastily built under difficult conditions in an attempt to contain the radioactive material resulting from an explosion at Reactor 4.

It was moderately successful, but in the decades since, work continued to find a better solution that would safely and securely contain the radioactive material from the remains of the reactor for the next century.

In 1992 the Ukraine government launched a competition to replace the sarcophagus, and in 2007 the contract to build the new structure was awarded.

The NSC is 275 metres wide, 108 metres tall, and cost $1.5 billion according to the European Bank for Reconstruction and Development.

It is designed to: