As Ukraine marks the 39th anniversary of the world's worst civilian nuclear accident at the Chernobyl power plant, engineers are struggling to find ways to repair the complex's protective shield more than two months after a Russian drone left a large hole in the structure.
The massive steel dome was designed to protect and confine the radioactive remains of crippled reactor number four that exploded when a routine safety test went wrong on April 26, 1986.
Radiation levels outside the punctured shield have stayed normal since the drone attack, officials say.
But sealing the hole hasn't been possible because it sits above the crumbling sarcophagus that encases radioactive debris from the reactor.
"How can you fix a roof space where the higher you go up in the building, the higher the radiation levels? They're so high next to the actual sarcophagus, the reactor unit, that you can't work above it," says Shaun Burnie, a nuclear expert with Greenpeace.
Burnie was part of a Greenpeace team invited to Chernobyl to inspect the damage shortly after the February 14 drone strike which Moscow denied it was responsible for.
"It's a very, very serious, enormous challenge for Ukraine at a time when it's faced with so many other challenges, and so the international community really needs to step in and support." says Burnie.
It took emergency crews three weeks to locate and extinguish fires that spread and smoldered through the membrane of the shield's outer shell.
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Ukraine Tries To Repair Chernobyl's Shield As Plant Marks Nuclear Disaster Anniversary (Video)
The new confinement structure was completed in 2019 as part of a $2.2 billion international project involving 45 countries. The temporary rail track used to install it over the reactor has since been dismantled, meaning the massive structure can't be moved safely to the side for repairs.
The United Nations predicted the shield would "make the reactor complex stable and environmentally safe for the next 100 years."
But long-term plans to safely dismantle the sarcophagus to allow the removal of radioactive ruins of the reactor are no longer possible following damage to the shield, according to Dmytro Humeniuk, an expert from Ukraine's State Scientific and Technical Center for Nuclear and Radiation Safety.
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The Chernobyl Disaster: How It Happened
The European Bank for Reconstruction and Development has earmarked $450,000 to assess the drone damage to the confinement structure.
Ukrainian Environment Minister Svitlana Hrynchuk estimates the preliminary results of the analysis should be completed sometime in May.
Repairs to the shield will be costly and Ukraine will need significant funding from international donors, predicts Burnie.
"They have to come up with a longer-term plan, which will be very extensive, very complicated, and potentially horrendously expensive."