The aftermath of the 1986 Chernobyl nuclear power plant explosion was as severe as it was vast, contaminating some 200,000 square kilometers (77,200 square miles) in Ukraine. Although Soviet Union officials initially put the number of fatalities at just 31, the United Nations estimates more than 3.5 million people were affected.

In the seven months after the explosion, construction crews raced to build a concrete-and-steel sarcophagus to contain the radioactive ruins. The accident and cleanup were high drama (enough to inspire their own HBO miniseries). Yet in the haste, the massive cover wasn’t completely stable and didn’t properly seal the reactor, prompting fears the sarcophagus would collapse and allow radioactive materials to escape once more into the atmosphere.

13% to 30%

Estimated portion of Chernobyl’s 190 metric tons of uranium that was sent into the atmosphere

36 hours

Time it took for officials to evacuate the nearby city of Pripyat, Ukraine

3.5 million

Number of people affected by Chernobyl, per U.N. estimates

“It was not built very sturdily, and that’s how it sat for years,” says Oscar McNeil, managing director, shelter implementation plan, project management unit, Bechtel.

That set the stage for a second-round cleanup, with the same high stakes and uncertainty. Bechtel would provide oversight to the €2.1 billion New Safe Confinement project launched in 1997 by the government of Ukraine and the European Bank for Reconstruction and Development. After more than a decade of planning to develop an airtight solution, French construction consortium Novarka set to work in 2011 to build a massive arch—intended to last for 100 years—that would encase toxic materials and allow other teams to dismantle the sarcophagus by 2023.

Yet the area still had high contamination levels, raising the question: How would Bechtel and Novarka convince anyone to work on the project?

US$235 billion

Cost of damage

10,000

Total number of workers on the site of the New Safe Confinement project

3,000 years

How long scientists estimate it might take until the immediate area around Chernobyl is inhabitable

Handle With Care

Project leaders knew they needed to pull in some of the world’s top experts in construction, engineering and commissioning. “But when we would ask people to come to Chernobyl, their first answer was, ‘I would never work there,’” says Cyrille Fargier, project director, New Safe Confinement project, Novarka.

The company set up a 70-member team dedicated to the control and prevention of radiation exposure. It positioned arch construction 300 meters (984 feet) from the reactor site to mitigate the risk of exposure to radiation. And anyone who worked close to the reactor site had to wear three different radiation-measuring devices. Once workers reached their daily maximum exposure—a lower limit than the industry standard—they had to leave the working area.

“When we would ask people to come to Chernobyl, their first answer was, ‘I would never work there.’”

Cyrille Fargier

New Safe Confinement project, Novarka

“We had a very conservative approach to radiation exposure and a very sophisticated tracking system,” Fargier says.

All of the safety protocols were communicated to potential hires and the up to 2,500 team members on site at any time. The measures helped secure experts from 26 nations who contributed invaluable insights. When building an airtight membrane inside the shell to seal off contaminants, for instance, the team leaned on experts who had developed a similar structure for missile doors inside French military submarines.

The safety concerns did contribute to a massive schedule crunch. Novarka project leaders realized at one point that the arch needed to be slid into place over the sarcophagus seven months sooner than scheduled. Doing so would give more time for testing the complex integrated control systems, electrical systems, climate control system and sealing membrane, among other features. The Novarka team sped up the process by checking systems as they were being installed. “If we had waited for all the construction work to be completed, which would have been ideal, we wouldn’t have met the deadline,” Fargier says.

The crunch also forced Bechtel’s team to innovate to accelerate work, according to McNeil. For example, the team had to build tall concrete walls inside one area of the sarcophagus to connect to the arch after it was slid into place. “We used sacrificial forms to place concrete in lifts,” McNeil says. “By leaving the forms in place, we didn’t have to wait for the concrete to completely cure before placing the next lift.”

There were other safety-related slowdowns: Crew members installing the shelter’s end walls on-site, for instance, could only work in 15-minute shifts in certain areas to prevent overexposure to radiation. Despite the delays, the project finished within budget. “We all realized the project objectives were bigger than any of us,” Fargier says. And the project’s safety record was sterling: a lost-time-injury rate 10 times lower than U.S. industry standards, McNeil says.

In April 2019, the testing phase ended with a 72-hour trial run. The arch is now the largest movable metal structure, taller than the Statue of Liberty and big enough to enclose Notre Dame Cathedral. It’s sturdy enough to withstand tornadoes, earthquakes and extreme temperatures.

“We’ve removed the risk of another nuclear catastrophe in Europe stemming from Chernobyl,” McNeil says. “All of us feel a great deal of pride in that.”