Associated Press

CHERNOBYL NUCLEAR POWER STATION, Ukraine — Workers have raised the first section of a colossal arch-shaped structure that eventually will cover the exploded nuclear reactor at the Chernobyl power station.

Project officials on Tuesday hailed the raising as a significant step in a complex effort to clean up the consequences of the 1986 explosion, the world’s worst nuclear accident. Upon completion, the shelter will be moved on tracks over the building containing the destroyed reactor, allowing work to begin on dismantling the reactor and disposing of radioactive waste.

Suma Chakrabati, president of the European Bank for Reconstruction and Development, which is leading the project, called Tuesday “a very significant milestone, which is a tribute to the ongoing commitment of the international donor community, and an important step towards overcoming the legacy of the accident.”

The shelter, shaped like a gargantuan Quonset hut, will be 257 meters by 150 meters (843 feet by 492 feet) when completed and at its apex will be higher than the Statue of Liberty.

The April 26, 1986, accident in the then-Soviet republic of Ukraine sent a cloud of radioactive fallout over much of Europe and forced the evacuation of about 115,000 people from the plant’s vicinity. A 30-kilometer (19-mile) area directly around the plant remains largely off-limits and the town of Pripyat, where the plant’s workers once lived, today is a ghostly ruin of deteriorating apartment towers.

At least 28 people have died of acute radiation sickness from close exposure to the shattered reactor and more than 6,000 cases of thyroid cancer have been detected in people who, as children or adolescents, were exposed to high levels of fallout after the blast.

Officials who showed reporters around the construction site Tuesday were clearly delighted at the colossus taking shape before them, but concerned about the challenges ahead. The shelter is to be moved over the reactor building by the end of 2015 — a deadline that no one wants to miss given that the so-called sarcophagus hastily built over the reactor building after the 1986 explosion has an estimated service life of about 30 years.

The arch now under construction is only one of two segments that will eventually form the shelter, and so far it’s only been raised to a height of 22 meters (72 feet). More structural elements have to be added before it reaches its full height of 108 meters (354 feet), and the work so far has taken seven months.

“There’s no room for error … the schedule is very tight,” said Vince Novak, director of the EBRD’s nuclear safety department, who added that staying within budget is also a concern.

The overall shelter project is budgeted at €1.54 billion ($2 billion) — €1 billion ($1.3 billion) of that for the structure itself — and much uncertainty lies ahead. One particular concern is dismantling the plant’s chimney, which must be taken down before the shelter is put in place. The chimney is lined with radioactive residue that could break up and enter the atmosphere as it is taken apart. Laurin Dodd, managing director of the shelter project management group, said some sort of fixative will have to be applied to the chimney’s interior.

“This is one of the most challenging parts, because it’s an unknown,” he said.

Other possible delays could come if excavations for the shelter’s foundation uncover radioactive waste or even buried machinery. Dodd said other excavations unearthed several bulldozers and cranes that had to be decontaminated.

Even when the shelter is in place, the area around the reactor building will remain hazardous. The shelter is aimed only at blocking radioactive material from escaping when the reactor is being dismantled; it won’t block radiation itself.

But when the dismantling and cleanup work is complete, the radiation danger will decline. How long that would take is unclear, but officials on Tuesday allowed themselves to envision a happier Chernobyl a century from now, with the plant’s director speculating that the huge shelter may even become a tourist attraction.

Plant director Igor Gramotkin drew a parallel between the shelter and the Eiffel Tower.

“Originally, that was intended to be destroyed. But I think this (shelter) will be so impressive that even in 100 years people will come to look at it,” he said.