"Despite the difficult conditions of radioactivity, the work was carried out to a high standard, with a high level of safety for personnel," Atomstroyexport said in a statement. The work involved repairs of an area around 420 square meters over the central part of the reactor’s protective shelter.

Atomstroyexport as a leader of the Stabilization consortium that also includes Ukrainian companies has carried out work on numerous occasions to reinforce the badly-worn sarcophagus.

The latest repairs were managed by the European Bank for Reconstruction and Development (EBRD) and carried out as part of the Chernobyl Shelter Fund, a project aimed at building a new sarcophagus over the reactor at an estimated cost of around $1.2 billion. The EBRD has pledged $507 million towards the massive construction project, the agency reported.

Estimates by international bodies as to the number of deaths caused by the Chernobyl accident vary dramatically. Fifty-six people were reported to have been killed at the scene of the disaster, and another 4,000 to have died of thyroid cancer shortly afterwards. Several million more people are believed to have been exposed to different degrees of radiation.

The disaster is thought to have released at least 100 times more radiation than the atomic bombs dropped on the Japanese cities of Nagasaki and Hiroshima in WWII.