An investigation is to be held into a derailment involving a nuclear freight train in Somerset on Thursday.
The flask was empty at the time of the locomotive's derailing
A Direct Rail Services (DRS) locomotive delivering an empty irradiated nuclear flask to Hinkley Point nuclear power station became partially derailed while travelling slowly at Bridgwater station.
A set of wheels slipped off the line just outside a secure nuclear compound where giant radioactive fuel containers from Sellafield are loaded and unloaded.
Flasks are heavily-shielded, purpose-built containers constructed from forged steel more than 30 cm thick.
Each flask weighs more than 50 tonnes and is housed under a locked cover, fastened to the rail wagon for transportation. with radioactive material being transported either by rail or road.
A spokesman for DRS said the incident happened in a freight yard away from the main line and involved one locomotive of a pair.
It did not have any effect on the flask, or the rail wagon carrying it, he said.
An investigation into the cause of the incident would follow, he added.