Over the next five days, engineers at Chernobyl, the Ukrainian site of the world’s worst nuclear disaster, will be moving an enormous roof over the still irradiated remains of the plant’s No 4 reactor.

Hopes are high that the new superstructure can contain radiation while Ukraine works to deal with the nuclear waste within the exploded reactor. Bellona’s executive director and nuclear physicist Nils Bøhmer, however, said the new roof will not entirely remove radiation dangers from the area.

Chernobyl’s reactor No 4 exploded on April 26, 1986, and over the ensuing 10 days, its nuclear fuel continued to burn, issuing clouds of poisonous radiation and contaminating as much as three quarters of the European continent, hitting northern Ukraine, Russia and Belarus, especially hard.

Sweden was the first country to report irregular radiation readings. The Chernobyl plant was the suspected culprit, but Soviet officials remained mum.

A group of Chernobyl liquidators getting ready to remove radioactive debris in 1986. Credit: Chernobyl.Wikia.com

In the days following, 116,000 people were evacuated while some 600,000 liquidators, comprised of police, fire fighters, military and engineers, operated in chaotic and dangerous conditions, often without protective gear, to implement a containment structure of cement and steel to squelch emissions of radiation.

The ad-hoc structure trapped 200 tons of uranium, but many liquidators feared at the time that the cement barrier would eventually give. In 2005 it did.

This week, the New Safe Confinement, a €1.5 billion ($1.6 billion), 36,000 ton steel structure, will slide into place with the goal of trapping that radiation for the next 100 years – by which point it is hope engineers will contain it for good.

Financed by donations of more than 40 countries coordinated by the European Bank of Reconstruction and Development, the New Safe Confinement is the largest movable land-based structure on earth, and will fully enclose the remains of Chernobyl’s No 4 reactor.

The arch structure is the largest moveable land-based structure ever built, with a span of 257 meters, a length of 162 meters, and a height of 108 meters. That’s big enough to house London’s St. Paul’s cathedral or Paris’s Notre Dame.

The London-based EBRD calls it “one of the most ambitious projects in the history of engineering.

The New Safe Confinement was constructed in a clean area near No 4 reactor and will over the next week slide a little more than 327 meters to seal off the unit, World Nuclear News reported.

It’s hoped to make the site safe to allow for eventual dismantling of the crumbling concrete shelter, called the sarcophagus, currently covering the remains of the reactor. It will also facilitate management of the waste within the structure, the EBRD said.

Most of this work will fall to a heavy-duty crane, operated remotely within the arch, as well as robotic tools suspended from the roof of the New Containment Structure.

Pripyat's Ferris Wheel, which has not turned since the evacuation. Photo: - Credit: Nils Bøhmer

Ostap Semerak, Minister of Ecology and Natural Resources of Ukraine, said in a statement that the structure is “the end of a 30-year long fight with the consequences of the 1986 accident. ”

Vince Novak, EBRD’s nuclear safety director, said “The new structure illustrates what is possible in a spirit of determined and coordinated joint effort and thanks to the generous support of EBRD shareholders.”

But risks remain that the high radiation levels may damage this equipment, just as robots entering Japan’s Fukushima nuclear plant, after the 2011 tsunami-induced disaster, were defeated by radioactivity.

“This is an important step to secure the environment from radioactive pollution to the region caused by the tragic accident of 30 years ago,” said Bellona’s Bøhmer. “Unfortunately, it will still take many decades until the whole risk posed by reactor No 4 at Chernobyl is eliminated.”

Indeed, even when the new shelter is in place, the surrounding exclusion zone of around 2,600 square kilometers will remain uninhabitable – and it will take another 20,000 years before people can live near the plant again.