Engineers at Chernobyl, Ukraine, are close to installing a new state-of-the-art protective shelter over the remains of reactor no. 4, the site of the worst nuclear power plant accident in history. The New Safe Confinement, a 30,000-ton structure that resembles a hangar the size of the Notre Dame cathedral in Paris, is the largest movable structure built. It will serve two purposes.

Drone footage shows Chernobyl's massive confinement dome (European Bank for Reconstruction and Development)

First, it will replace the "sarcophagus," the temporary, steel-and-concrete shelter hastily assembled by an army of 600,000 Soviet workers in 1986. Built in just six months, it was a herculean and heroic effort that largely managed to contain the radiation not initially released in the accident. It was also costly in human life, as many of the "liquidators" did not have proper safety equipment. In an interview with The Washington Post, one man who helped build the sarcophagus said he had undergone eight heart and kidney operations because of complications from the radiation.

The shelter was not meant to last longer than 20 to 30 years, and the structure has visibly deteriorated with time. Engineers, concerned that a collapse of the sarcophagus could lead to a new release of radioactive dust into the environment, began plans in 1997 for the New Safe Confinement in a project led by the European Bank for Reconstruction and Development. In 2017, the New Safe Confinement will be wheeled into place over the sarcophagus and sealed, providing a new shelter. Then, heavy-duty cranes inside the New Safe Confinement will disassemble the sarcophagus.

The second task is waste management. According to the EBRD, there are more than 200 tons of uranium mixed with sand, lead and boric acid in a "lava like mass" in the reactor. The mixture is the "most significant radiological hazard at the site." Levels of radioactivity are particularly high directly over the reactor. Rather than place workers there to build the roof of the New Safe Confinement, engineers decided to build a structure that could be wheeled into place instead. There are other sources of radioactive waste, too, including fuel assemblies from reactors 1 to 3 of Chernobyl, the last of which ceased working in 2000.

Chernobyl still dangerous 30 years after meltdown (Reuters)

Various sites for waste disposal are being built under the Shelter Implementation Plan, the 2.1 billion-euro ($2.36 billion) road map to making the accident site safe. Liquid radioactive waste will be mixed with cement at a special plant to bring it to a solid state. A storage facility built with international financial support will hold spent fuel collected from the reactor site.

One of the main questions for the future is cost. International donors, particularly the EBRD, the European Commission and the United States gave most of the funding for the Shelter Implementation Plan. But as of next year, the Ukrainian government, which has faced severe strain because of geopolitical and economic concerns, will be expected to manage the waste disposal process largely on its own.

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