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KIEV, Ukraine (AP) — A structure built to confine radioactive dust from the nuclear reactor at the center of the 1986 Chernobyl disaster was formally unveiled on Wednesday.

Ukrainian President Volodymyr Zelenskiy inaugurated the "new safe confinement" shelter that spans the remains of the Chernobyl nuclear power plant's Reactor No. 4.

The enclosure cost 1.5 billion euros (almost $1.7 billion) to build, and the project took nine years to complete and cost 2.2 billion euros (about $2.5 billion) in all.

Officials have described the reactor enclosure as the largest moveable land-based structure ever built, with a span of 257 meters (843 feet) and a total weight of over 36,000 metric tons (over 40,000 tons.)

Reactor No. 4 at the plant in what was then Soviet Ukraine exploded and burned on April 26, 1986. The disaster's eventual death toll is subject to speculation and dispute.

The World Health Organization's cancer research arm estimates that 9,000 people will die of exposure-related cancer and leukemia if Chernobyl disaster's health effects follow a similar pattern to the Hiroshima and Nagasaki atomic bombings.

About 350,000 people were evacuated from the explosion area in the early days after the accident. About 600,000 people had exposure to radiation at elevated levels while fighting the fire at the plant or working to clean up the contamination.

The new confinement structure was designed to keep radioactive dust from moving and as a safeguard from further crumbling of the reactor. A section of the machine hall collapsed in 2012.

Deputy project manager Victor Zalizetskyi, who has been part of construction and repairs at the Chernobyl plant since 1987, said he was "filled with pride" that he got to work on a job "that has such a big importance for all humankind."

However, Zalizetskyi expressed concern in an interview last week that war-torn Ukraine might struggle to cover the maintenance costs for the reactor's new enclosure. He noted that costly and complicated work such as dismantling unstable sections of the power plant still needs to be done.

"It looks like Ukraine will be left alone to deal with this structure," he said. "The work is not done yet, and we need to think about how to finance this project in the future."

To finance the containment structure, the European Bank for Reconstruction and Development managed a fund with contributions from 45 countries, the European Union and the bank's own resources. Ukraine contributed 100 million euros (about $112 million).

The Associated Press