Four primarv types of package (i. e., container or pack­aging, together with contents) are defined: Excepted,

Industrial, Type A and Type u. In a graded approach the design requirements and, where appropriate, stand­ard tests and performance criteria are specified. They become more stringent as the hazard represented by the contents increases. Thus there are no specific per­formance standards for the lowest group excepted packages, whereas Type A packages are intended to withstand normal transport conditions and Type В packages to survive very severe accidents.

For Type A packages the contents are restricted so that in the event of an accident which damaged the container, the resulting radiation dose to a person at the scene of the accident would be unlikely to ex­ceed the appropriate annual dose limit for a radiation worker.

In general, application of standard dosimetric mod­els to a given radionuclide results in two limits for the amount of that radionuclide in a Type A package. The first limit (Ai) is based on the external radiation exposure due to loss of shielding, and if the radio­nuclide was non-dispersible or ‘special form’, e. g., a sealed source, then this limit would apply. The second limit is based on release of some of the radioactivity in a dispersible form, and the resulting radiation dose by inhalation, ingestion, skin contamination and other routes.

The lower of the two limits is known as the Ai value and it represents the contents limits for a Type A package with contents in dispersible form.

A2 values are tabulated for most radionuclides and they represent a common basis of hazard potential. There are rules for determining the effective A2 value for mixtures of nuclides, and the general rules for package content and leakage limits are expressed in multiples of sub-multiples of A2 values.

The contents of excepted and industrial packaging are limited such that they would present no greater hazard in the event of an accident, than the Type A package. The activity allowed in an excepted package is severely limited in recognition of the fact that this package is not expected to retain its contents after an accident. The contents of the three grades of industrial package are restricted to low specific activity (LSA) materials or to surface contaminated objects (SCO), whose potential hazard is limited by the re­latively low toxicity of the inaccessible nature of their radioactivity content.

For Type В packages no direct limit on radioactive content is specified. However, a series of tests are prescribed which simulate the damage which could be sustained in a very severe accident. These include a drop test from 9 metres onto an unyielding target, and a punch test in which the package is dropped from 1 metre onto a rigid bar. These tests are carried out in the order and attitudes which would maximise the consequences of a subsequent thermal test which involves the complete engulfment of the package for half an hour in a hydrocarbon fuel/air fire with an average flame temperature of at least 800°C. A maxi­
mum leakage rate of radioactivity following these tests is specified, and also a maximum external radiation dose rate. These requirements, together with those for normal transport and consideration of heat dis­sipation requirements, limit indirectly the radioactive contents of Type В packages.

In specifying design requirements for Type В pack­ages, the Regulations prescribe standard conditions of ambient temperature and solar isolation. However, relaxation from these conditions is allowed, provided that the use of the package is appropriately restricted to wnthin a specific country or between specified coun­tries. Packages which are approved on this basis are designated as Type В (M), as distinct from Type В (U) packages which meet the worldwide standards.

For the purpose of controlling the radiation dose to transport workers and members of the public under normal transport conditions, appropriate segregation of packages is required. A limiting annual dose for individuals in each group is indicated as a guide to the minimum requirements for segregation distances, and to allowable dose rates in regularly occupied areas.

Segregation of packages from undeveloped photo­graphic film is also a requirement.

To facilitate control, packages are categorised and labelled on the basis of the radiation’dose rates at the surface and of the package and at 1 metre from the surface (see Table 4.12). The latter dose rate (in mSv/h x 100) is known as the ‘transport index’. This, infor­mation is given on the package label. Loading controls include limits on the sum of the transport indices of packages carried in a single conveyance. Limits are also placed on the radiation levels at the external surfaces of transport vehicles, and at 2 metres from the surface.

Limits are also specified for non-fixed contamina­tion on the external surfaces of packages. For packages
other than ‘Excepted packages’ these limits are 4 Bq/cm2 (10 ~4 Сі/cm2) of beta/gamma emitters and low toxicity alpha emitters, and 0.4 Bq/cm2 (10 ~5 Сі/ cm2) for all other alpha emitters. The corresponding limits for Excepted packages are a factor of ten lower. In the case of packages containing fissile material, the hazard of nuclear criticality has to be considered in addition to the basic radiation and contamination control aspects. In order to ensure that the risk of criticality under normal and accident conditions is made practically non-existent, appropriate design re­quirements and tests are described for fissile packages.

Interaction between packages is allowed for by de­fining a nuclear criticality transport index, and by limiting the sum of the transport indices of packages transported together. The transport index is always the higher of the dose rate and criticality transport indices.