On the 26th anniversary of the Chernobyl nuclear disaster Thursday, Ukraine officially launched the construction of a new radiation shell to cover radioactive materials as the current one is getting old and degrading.

Ukranian President Viktor Yanukovych spoke during a ceremony inaugurating the initial assembly of the 20,000 ton structure known as the "sarcophagus".

"On behalf of Ukraine I express my gratitude to all donor countries the Chernobyl Fund 'Shelter' for their understanding and active support of our country to overcome the biggest disaster in human history," he said at the ceremony.

“We never stop taking care of the safety of the covering of the fourth reactor,” he added.

In the early hours of April 26, 1986, No. 4 reactor at the Chernobyl nuclear plant exploded, spewing a radioactive cloud into the air, forcing hundreds of thousands from their homes in heavily hit areas of Ukraine, Belarus and western Russia.

For the anniversary, Yanukovych and the country’s minister of emergency situations, Viktor Baloga, placed flowers at the site before attending the official launch ceremony.

The shell is expected to take three and a half years to complete, with the total cost estimated at 1.6 billion euros ($2.1 billion).

Below is a video describing the structure: