ST-1 is now in force

Since the IAEA first published its transport regulations in 1961, the regulations have been comprehensively revised at intervals of about ten years. In December 1996 the IAEA published the “Regulations for the safe transport of radioactive material” in a document designated ST-1 which came into force on 1 January, 2001.

One of the major changes in ST-1 is the explicit requirement for the establishment of a radiation protection programme for the transport of radioactive material. The radiation protection programme includes:

•Scope of the programme.

•Responsibilities to implement it.

•Dose assessment.

•Surface containment assessment.

•Dose limits, dose constraints and optimisation.

•Segregation doses.

•Emergency response.

•Training.

•Quality assurance.

Programme scope

The radiation protection programme should include all aspects of transport covered by the scope of the regulations. However, these will often be covered by existing radiation protection programmes at fixed sites.

Similarly, the extent of a particular programme will vary considerably depending on the package categories and types routinely consigned. For example, a nuclear power facility shipping spent reactor fuel elements would be expected to have a much larger programme than a research institute shipping small quantities of material.

Roles and responsibilities

Many parties are involved in transporting radioactive material. Each of their roles and responsibilities must be identified and described in the radiation protection programme. This has to be done so as to avoid overlapping responsibilities.

Dose assessment

Dose assessment is an important part of the programme because the regulations base individual monitoring requirements and the use of segregation on likely exposures.

Under ST-1, the annual dose divisions between the three monitoring categories have been changed. For exposures from transport activities:

•Where effective dose is most unlikely to exceed 1mSv in a year, neither special work pattern nor dose assessment programmes nor individual record keeping are required.

•Where effective dose is likely to be 1-6mSv in a year, a dose assessment via work place monitoring or individual monitoring shall be conducted.

•Where effective dose is likely to exceed 6mSv in a year, individual monitoring is required.

Exemption

Previous regulations defined radioactive material as any materials with a specific activity greater than 70Bq/g. The regulation now defines a radionuclide specific approach. There are now individual exemptions for each nuclide. The new regulations contain both activity concentration and total activity per consignment exemption values.

Materials transported in the nuclear fuel cycle are not affected by this change, as their activity is well above any exemption value.

Surface contamination

Previously, a distinction was made between the limits for non-fixed surface contamination for excepted packages and those for other packages. In ST-1, the reduction by a factor of ten for excepted packages has been removed.

The new regulation is “The non-fixed contamination on the external surfaces of any package shall be kept as low as practicable and, under routine conditions of transport, shall not exceed the following limits:

•4Bq/cm2 for beta and gamma emitters and low toxicity alpha emitters.

•0.4Bq/cm2 for all other alpha emitters.

These limits are applicable when averaged over any area of 300cm2 of any part of the surface.”

Packaging

Fissile exceptions

There have been some changes to the requirements for packages containing fissile material to improve clarity.

A mass limit per consignment has been introduced into ST-1 for three exception categories which had previously relied upon packaging to maintain subcriticality. These categories are (a) packages containing not more than 15g of fissile material and (b) packages containing not more than 5g of fissile material in any 10l volume, and fissile material in a homogenous hydrogenous solution or mixture where the ratio of fissile nuclides to hydrogen is less than 5% by mass.

Reliance on packaging for fissile exceptions is erroneous, especially in accident conditions where neither the geometry nor the degree of moderation can be guaranteed. The mass limit per consignment was introduced to dissuade a consignor from circumventing the regulations by transporting a very large number of packages each containing just less than the excepted quantity limit. Under ST-1, only one type of fissile exception per consigment is allowed, which is more cautious than the SS No. 6 fissile exceptions which applied to packages meeting one of the six exception categories.

Air transport

The decision to introduce a more robust package for the air transport of radioactive material led to a consequential decision to provide equivalent protection against accidental criticality in air transport for all fissile material. ST-1 has therefore introduced a new package specification, Type C, which will apply to the transport of large quantities of radioactive material by air. The introduction of the Type C package places a content limit on Type B(U) and Type B(M) packages travelling by air. The current limits are:

•3000A1 or 100,000A2, whichever is lower, for material in special form.

•3000A2 for all other forms of radioactive material.

Individual fissile packages will have to be designed to be subcritical under conditions consistent with the tests for Type C packages, if they are to be used for air transport. This precludes extremely large criticality events that can occur when initiated by a rapid change in geometry. Worst case assumptions regarding geometric changes and rearrangement of components will need to be made, unless other assumptions can be supported after a specimen has been subjected to the enhanced test requirements.

Crush test

ST-1 has introduced an additional fissile related criterion such that a crush test is required for all packages with a mass no greater than 500kg and a density not greater than 1000kg/m3. The test requirement is applied to all those packages containing fissile material that are considered most vulnerable to crushing. Previously, the test was applied only to fissile packages if they contained more than 1000A2 not in special form.

Test criteria

Type C packages are required to undergo the following cumulative test sequences, after which they must be shown to retain their radioactive contents and shielding properties within defined limits. Like Type B(U) and Type B(M) packages, they must restrict loss of radioactive contents to no more than A2 in a week and restrict the radiation level at 1m from the package surface to not more than 10mSv/h.

In addition, Type C packages must be shown to meet the same containment and shielding criteria as those above when subjected to burial and must be shown not to rupture when immersed in 200m deep water. The requirement to demonstrate the ability to withstand burial is done by assessment, assuming the package to be undamaged, buried in dry soil at 38°C in a steady state condition.

LDM considerations

ST-1 has introduced a new specification for low dispersible radioactive material. This specification recognises that certain radioactive materials, which by their nature are solids of limited dispersibility, limited solubility and with a limited external radiation field (not exceeding 10mSv/h at 3m from the unshielded material), may be safely carried by air.

The specification for low dispersible radioactive material requires that separate specimins of the material be subjected to the 90m/s impact test and the 800°C thermal test for one hour, followed by a leaching test. The pass criteria are that no more than 100A2 of material shall be released in either case.

MARKING

There are several small changes in required marking associated with ST-1.

In each case, the purpose is to provide information for those handling the package, and to facilitate communication of useful information to emergency response personnel if needed.

Each package must now be marked on the outside of the packaging with an identification of the consignor or the consignee, or both. This may consist of the name and address, or it may be a number identifying a way-bill or transport document which contains this information.

ST-1 requires that each package, other than excepted packages, be marked with its UN number (preceded by the letters “UN”) and its proper shipping name.

New numbers and schedules

It has long been recognised that many of the existing UN numbers for Class 7 material were not as useful as they could be. For example, the most common number, UN 2982, does not provide any more information about the material being transported other than the fact that it is radioactive. Since the primary purpose of displaying UN numbers on packages and on conveyances is to provide a key into emergency response procedures in a language-independent way, it was decided to revamp the numbering system so that it might lead to more useful response procedures.

Similarly, the schedules which were formerly in Safety Series No 80 (17) are more useful if they have a direct relationship with UN numbers. In this case, any one UN number would lead to only one schedule where the user will find most of the references and regulations needed to make that particular consignment. This is the case in the new numbering system developed for ST-1, where a UN number is assigned to each of the schedules.

The schedules are now appended to the regulations instead of being in a separate document and therefore SS-80 is superseded by ST-1. The existing UN numbers for UF6 were retained because of its importance as a commercial substance and its significant subsidiary risk. However, a separate set of numbers was assigned for packages containing fissile material.

UF6

Previously, the regulations did not specifically address UF6, but dealt with its fissile and radiological considerations in the same manner as any other material. ST-1 has written regulations for the packaging of UF6.

The additional requirements for packages containing UF6 do not apply to packages containing less than 0.1kg of UF6. Packages designed to contain more than 0.1kg of UF6 must:

•Withstand an internal pressure of at least 2.8MPa.

•Withstand the Type A drop test.

•Meet the Type B thermal test of 800°C for 30 minutes if designed to contain less than 9000kg of UF6.

•Either meet the thermal test requirement or have multilateral approval if designed to contain 9000kg or more of UF6.

•If containing fissile UF6, meet the test conditions applicable to fissile packages with no contact between the valve and other normally non-contacting parts of the packagings; no leakage from the valve; and meet other operational requirements before the designer can assume no in-leakage of water for the criticality safety analysis.

•Have unilateral competant authority design approval after 31 December 2003, with certain exceptions.

The complexity of these requirements comes from the desire to address the areas of safety concern, while pragmatically recognising the real-world situation with respect to existing containers and older package designs.

Transport index

The purpose of the transport index has been to limit the hazards associated with the accumulation of radioactive material packages. There are two hazards: radiation dose rates and inadvertent criticality. Since the beginning of the regulations, the TI has been used for both purposes, and this arrangement has worked reasonably well. However, it did give rise to situations which were overly conservative and also resulted in several other difficulties and ambiguities. Part of the problem lay in the fact that for some applications, there was a need to know how the TI was derived (radiation or criticality) to properly apply it.

ST-1 solves these problems by treating the two hazards separately and giving each its own index. The consequence is that the TI has been greatly simplified in that it now only applies for radiation protection purposes. It continues to be based on the radiation level at 1m from the package surface.

Criticality safety index

Criticality safety index (CSI) limits the accumulation of packages solely based on criticality considerations. The method of calculation is the same as that previously used when the TI was being determined for criticality safety purposes.

The introduction of the separate CSI necessitated a new label for all packages containing fissile material. CSI labels must be affixed adjacent to the radioactivity category labels. Similarly, the CSI also must be included on the transport documents for fissile consignments.

Transitional arrangements

Whenever the regulations are revised, there is the potential to make existing package designs and packagings obsolete. Since packages designed under earlier editions of the regulations have performed well in practice, it has been common to provide transitional arrangements, also known as ‘grandfathering’ provisions, to allow their continued use within certain constraints and time limits. This concept is maintained in ST-1. However, some requirements such as the Type C package come into force immediately.