Transportation of radioactive materials
The transport of radioactive materials within the UK is governed by strict regulations
The general requirements for all packaging and packages used for the transportation of radioactive substances and articles are that:
- The package shall be so easily and safely transported and shall be designed that it can be properly secured in or on the conveyance during transport
- Any lifting attachments on the package will not fail when used in the intended manner and shall take account of appropriate safety factors to cover snatch lifting
- As far as practicable, the packaging shall be designed and finished so that the external surfaces are free from protruding features and can be easily decontaminated
- As far as practicable, the outer layer of the package shall prevent the collection and the retention of water. Any features added to the package at the time of transport that are not part of the package shall not reduce its safety.
- The package shall be capable of withstanding the effects of any acceleration, vibration or vibration resonance. In particular, nuts, bolts and other securing devices shall be designed as to prevent them from becoming loose or being released unintentionally, even after repeated use.
- The materials of the packaging and any components or structures shall be physically and chemically compatible with each other and with the radioactive contents. Account shall be taken of their behaviour under irradiation.
- All valves through which the radioactive contents could otherwise escape shall be protected against unauthorised operation
- The design of the package shall take into account ambient temperatures and pressures that are likely to be encountered in routine conditions of transport
- For radioactive material having other dangerous properties, the package design shall take into account those properties.
There are five basic container types for the transportation of radioactive materials:
- Excepted packages: may survive a minor accident
- Industrial packages: may survive a minor accident
- Type A packages: survive a minor accident
- Type B packages: survive a major accident
- Type C packages: survive an air accident
These are for certain very small quantities of radioactive materials, marking with the UN number is a requirement under the latest transport regulations. Common examples are radiopharmaceuticals, calibration sources and some experimental apparatus. Surface dose rates must be below 0.005 mSv per hour. Excepted packages can be conveyed by all modes of transport in the UK (including the postal service)
These are for materials with very low concentrations of radioactive material, possibly also in forms that are not easily dispersed. They are basic containers used for materials of low specific activity (LSA) or surface contaminated objects (SCO), such as natural uranium ores or depleted uranium and worn protective clothing such as gloves and overalls. These containers are not necessarily expected to survive accident conditions. These packages are usually transported by road, rail or sea, although some air transport does occur.
Type A packages
These are for relatively large quantities of radioactive materials (compared with Industrial packages) such as radiopharmaceuticals or radiochemical. Packages are designed to withstand minor accidents and only release a small fraction of their contents in a more serious accident. Surface dose rates are normally limited to no more than 2 mSv per hour. These packages are normally conveyed by all modes of transport, especially air, as this reduces travel time for short-lived isotopes.
Type B packages
These are for larger amounts of radioactive materials, such as irradiated nuclear fuel, nuclear wastes or large radiation sources for radiotherapy. They are very strong packages and typically contain large quantities of radioactive material. They are specially designed containers able to withstand accident conditions. Surface dose rates are generally much less than 1 mSv per hour, and are limited to 2 mSv per hour under standard conditions. Type B packages are the predominant package type conveyed by rail, they are also transported by road, air and sea.
Type C packages
These are for large amounts of radioactive materials carried by air. They are robustly designed packages for high-activity dispersible sources, including fissile material exclusively for air transport. Testing these packages ensures that the package remains intact should it be involved in an air accident. Type C packages are relatively rare internationally.
In nuclear engineering, a fissile material is one that is capable of sustaining a chain reaction of nuclear fission. Fissile materials can be used to fuel:
- A nuclear reactor (e.g. at a nuclear power station)
- A nuclear explosive
Fissile material can be carried in industrial packages, Type A packages, Type B packages or Type C packages, but in this case the package will be designed to withstand accidents similar to the Type B or Type C package.
An additional type of package is used for uranium hexafluoride. These packages may be any of the above types (except not normally Type C). However, they require special treatment in emergencies, particularly in fires. These packages are normally cylindrical and range in size. They may be contained in a protective outer box, which gives the package protection against severe accidents. The material they carry is corrosive in nature, reacting with water to form hydrofluoric acid and this may be the major concern in an emergency. The radioactive material they carry is often of such a low concentration that there is little risk from radiation.