BNFL plans to fly plutonium waste from Europe and Japan to Sellafield, enrich it and send it back again.
The company issued a briefing after a row erupted over its plans and after the Transport Minister, Gavin Strang, agreed to hold urgent talks with the Labour MP, Denis MacShane, whose constituency of Rotherham in South Yorkshire, lies on the flight path.
Mr MacShane wants the flights banned amid growing fears that a plane crash could put millions of lives at risk and contaminate huge tracts of the country for generations.
However, BNFL insisted that the material being flown now was not nuclear waste and not nuclear fuel being imported for reprocessing.
"MOX fuel and other nuclear materials have been transported by air from Carlisle airport for a number of years, in complete safety," the company said.
"We have never made a secret of this - in fact we have publicised it through presentations and international conferences."
Environmentalists called for an immediate halt to the trade and there was alarm among local fire and emergency service chiefs over the implications of a possible crash or terrorist activity.
The Environment Agency is studying the issue of transporting nuclear materials by air.Reuse content