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World Nuclear Transport Institute

What are back end materials?

The nuclear fuel cycle can be broken down into what is generally known as the 'front end' and 'back end' operations. The front end covers the operations from the mining of uranium to the manufacture of fuel assemblies for loading into the reactors. The back end covers the operations concerned with spent fuel that leaves reactors.

 Nuclear -fuel -cycle

Fuel used in a nuclear power plant generates electricity for about five years. After this time it becomes less efficient and needs to be replaced. This spent fuel still contains 96% of the original uranium, 1% of plutonium, and also about 3% of fission waste products. At this stage, spent fuel can either be sent for storage pending final disposal, or reprocessed to recover the uranium and plutonium. 

The reusable uranium and plutonium can be used to produce new fuel such as Mixed Oxide (MOX) fuel. The 3% waste is transformed into a solid, insoluble glass form by a vitrification process and stored pending final disposal, for instance into a deep geological repository.

Spent fuel

Spent nuclear fuel is intensely radioactive. It is transferred first from the reactor to the on-site storage ponds for shielding and to allow radioactivity to decay. For subsequent transport off the reactor site, either to off-site storage or to reprocessing facilities at home or abroad, it is transported in high-integrity packages, known as casks. These casks are massively constructed from steel weighing typically around 100 tonnes. 

Spent fuel is transported extensively by rail across Western Europe and also by sea in Sweden, and from the Far East to reprocessing plants in France and the UK. Sea transport is by specialist ships designed and operated according to the Irradiated Nuclear Fuel (INF) Code of the International Maritime Organization (IMO).

Rail Transport Of Spent Fuel Heavy Load

Vitrified high-level waste

Vitrified high-level waste from the reprocessing of spent fuel is stored temporarily at the reprocessing plant to allow fission product heating to decay before it is returned to the country of origin. The transport casks are similar in design and construction to those for spent fuel and the transport operations whether by rail or sea also are similar. Several sea and rail shipments of vitrified waste have been successfully carried out.

Mixed oxide fuel (MOX fuel)

The plutonium derived from the commercial reprocessing of spent fuel is normally returned to the country of origin in the form of new mixed plutonium/uranium oxide fuel (MOX fuel) elements in which the enriched uranium isotope is replaced by plutonium. They are transported under special conditions by road or rail and in specialist vessels for sea transport. Extensive experience in MOX transport has been built up in Western Europe over many years and recently also by sea from Europe to the Far East. MOX fuel has been safely generating electricity in nuclear power plants around the world since the 1960s.


Specialised transport companies

Experienced and specialised companies have safely and securely transported back end materials on an industrial scale for over 50 years. These companies have developed transport systems and carefully manage back end transports around the world following required safety procedures. Comprehensive emergency response plans are in place, incorporating emergency arrangements for all modes of transport. These plans are routinely tested to ensure that public health and the environment are well protected in the event of an incident.


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