Serbia has sent 2.5 tons of its remaining nuclear waste, including highly-enriched uranium from a nuclear research facility near Belgrade, to a disposal site in Russia. The month-long secret operation was the largest single shipment made to return such nuclear material to the country where it originally came from. However, details of the route are classified to prevent terrorists from hijacking the cargo.

The BBC’s Gordon Corera discusses what he saw as the only journalist allowed on its route.