Work began in recent days to remove, bit by bit, the giant chimney protruding from the Chernobyl nuclear power station. It's one small part of a mammoth engineering project, now nearing completion, designed to slash the risk of another major release of radioactivity.

Massive and glittering in the weak winter sunshine, a half-built arch looms over Chernobyl's decaying industrial landscape of cooling towers and power lines.

One of the biggest engineering projects in history, it has been likened to a gigantic metal igloo, built to seal off hundreds of tons of nuclear fuel and dust buried inside reactor number four, which in 1986 blew up and burned for 10 days.

Everything about the project is epic: the size, the 1.5bn euro (£1.2bn) cost, the technical problems of working on a radioactive building site....