Nuclear flask

  A Nuclear Flask is a railway wagon which is used to transport waste nuclear materials between many power stations in the UK. A nuclear flask consists of 4 layers - a container flask, a 5" thick flask protector, a 12" thick flask and a 2" thick layer of steel panels.

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The flask is protected by a bolt hasp which prevents the content from being accessed during transit.

Greenpeace have protested the flask saying that it is not safe for passengers standing on platforms, although many tests performed by the HSE have proved that it is perfectly safe for passengers to stand on the platform while a flask passes through.

The flasks were tested when built when a 100mph locomotive hit a nuclear flask on the track, no content was detected despite the container being written off. Nuclear protesters consider the testing flawed for various reasons. The heat test used was 800C which is below that of theoretical worst case fires in a tunnel. In addition the impact test was at 100mph while the worst case impact today is about 170mph. Nevertheless there have been several embarrassing accidents involving flasks, including a derailment in Devonport, a collision with a road vehicle and a container being dropped during transfer from train to road. In all of these cases no leakage occurred.

Problems have however been found where the flasks 'sweat' - where small amounts of radioactive material absorbed into paint migrate to the surface causing contamination risks. Studies identified that 10-15% of flasks in the United Kingdom were suffering from this problem but none exceeded the international recommended safety limits. Similar flasks in mainland europe were found to exceed the safety during testing and additional monitoring procedures were put into place. In order to reduce the risk current UK flask wagons are fitted with a lockable cover to ensure any surface contamination remains within the container and all containers are tested before shipment, with those exceeding the safety level being cleaned until they are within the limit.

Probably the most comprehensive safety study was "Nuclear Waste Trains Investigative Committee: Scrutiny of the transportation of nuclear waste by train through London, October 2001". This report identified risks in the areas of emergency polices and particularly in the area of security of sites such as marshalling yards where there was a risk of terrorist attack.

The flasks weigh 50 tonnes and are all owned by the Nuclear Decommissioning Authority (owners of Direct Rail Services).

A typical Nuclear train consists of 2 x BR Class 20 or 2 x BR Class 37 locomotives (One locomotive provides power and the second is used as a breakdown assistance locomotive). Occasionally, both classes are used in a Class 20 + Class 37 + x-number of Flask wagons formation. DRS Class 66 locomotives are increasingly being used on these trains.

See also

• Spent nuclear fuel shipping cask