World’s largest moveable structure being built – the Chernobyl sarcophagus

Chernobyl: Containing the world’s worst nuclear accident BBC News [excellent photographs] David Shukman Science editor 18 March 2015 Rising above the scene of the world’s worst nuclear accident is the spectacular sight of the largest moveable structure ever created on land.The complex of nuclear power plants at Chernobyl has dominated this corner of northwest Ukraine for decades but the new construction towers over it all.

The project is to build what is called a New Safe Confinement – in effect, a giant cover, a kind of dome, to fit over the building that houses the reactor that exploded on 26 April, 1986.

The radiation immediately above the reactor is still far too intense for the new enclosure to be built exactly where it is needed – anyone working there can only stay very briefly. So adjacent land has been cleared and then decontaminated – a massive task in itself – to allow the new structure to be assembled before being manoeuvred into position.

Sealed future Large enough to accommodate a couple of Boeing 747s or the Stade de France in Paris, and almost tall enough to hold St Paul’s Cathedral in London, the giant cover stands on a system of massive rails.

When complete, it will weigh an extraordinary 31,000 tonnes. Over several days, it will be rolled along its special track so as to just slide over the reactor building – a very tight fit – in order to seal it in.
There is still a 30km exclusion zone around the Chernobyl site

The task is “of a complexity and uniqueness we have never faced before”, according to Vince Novak, who runs the nuclear safety department of the European Bank for Reconstruction and Development. He has led the international drive to make Chernobyl less dangerous.

“Until this project is in place, we will not be safe,” he said during a media visit to the site.

“The ultimate objective is to protect the environment, contain the threat and deal with the radioactive material inside.”

Dangerous mix

This material is a nightmare mix of more than 100 tonnes of uranium, one tonne of plutonium, and other highly radioactive elements, formed into a previously-unseen lava-like mass.
Added to that are several thousand tonnes of sand and boron dropped on to the site by emergency workers at the time.

Vast quantities of radioactive liquids and dust are also present inside a reactor building that has itself long been in danger of collapse. In the months following the accident – when the reactor exploded and burned for 10 days – the authorities attempted to smother the building in an emergency “sarcophagus” of concrete and steel.

But this was only ever intended to be a temporary fix and has needed urgent repairs to try to keep it stable and intact………http://www.bbc.com/news/science-environment-31939778