A makeshift sarcophagus built in the explosion’s aftermath was supposed to protect the environment from radiation for at least 30 years. But it has since developed cracks.

The project to build a new radiation container had been due for completion this year but the deadline was pushed to November 2017, as costs mushroomed from an initial estimate of €800 million to more than €2.15 billion now.

International donors agreed to pay an extra 180 million euros to fund the construction of a new cover for the disused Chernobyl nuclear power plant at a conference in London on Wednesday.

“Chernobyl pledging event raises 180 million euros to close funding gap,” the European Bank for Reconstruction and Development (EBRD), which is managing the talks, said in a statement.

The main share — 165 million euros — was pledged by members of the G7 nations and the European Commission.

The money comes on top of 350 million euros promised by the EBRD in November and the bank said the funding gap for the new project had now been reduced to 85 million euros.

Work on a new 20,000-ton steel cover at Ukraine's Chernobyl plant is ongoing, with officials saying the new cover will last for 100 years.

The explosion of Chernobyl reactor №4 on April 26, 1986, sent a poisonous radiation cloud large parts of Europe, mostly Ukraine, Belarus and Russia.