Reactor No 4 at the Chernobyl nuclear power plant in Ukraine exploded and burned down on April 26, 1986.
The complex construction effort to secure the molten reactor's core and 200 tonnes of highly radioactive material has taken nine years to complete under the auspices of the European Bank for Reconstruction and Development.
The entire shelter project cost around €2.1 billion.
The European Bank for Reconstruction and Development managed a fund with contributions from 45 countries, the European Union, as well as €715 million of the bank's own resources.
The shelter is the largest moveable land-based structure ever built, with a span of 257 metres and a total weight of over 36,000 tonnes.