Igor Gramotkin is ... the manager of the Chernobyl nuclear power plant in Ukraine, and has spent more than two decades at the site of the most devastating nuclear accident in history, trying to stop further radiation emissions and cleaning the area. Mr Gramotkin admitted that the destroyed reactor, still full of radioactive waste and nuclear fuel, remains a threat not only to Ukraine but to the whole world" until it is encased in a vast steel structure that is being built. In the months after the accident, a makeshift "sarcophagus" had been constructed to encase the reactor, but it is now unstable and, despite work to shore it up, experts say a new shelter is desperately needed in case the old one collapses. At more than 100m tall, the shelter will be the largest moveable structure ever built. Those building it still have to be extremely careful. Standing in the area immediately around the plant subjects a person to radiation equivalent to about one old-style chest X-ray per day. The human costs of the Chernobyl accident are ... horrific by any estimate. [Some] studies put the figure in the hundreds of thousands. There are incidences of genetic mutations, children born lacking organs, and dramatically elevated thyroid cancer levels in local children, who drank milk contaminated with radioactive iodine in the years after the accident.