“Alternative Requirements ”
8.8.2. Requirements for Type B(M) packages
For a variety of reasons, it is sometimes necessary to transport significant quantities of radioactive material in packages which have been designed, manufactured and tested to criteria which do not exactly conform to those given in the Regulations for Type B(U) packages. This may be possible using a Type B(M) package, within a specific country or solely between specified countries, with the specific approval of the Competent Authorities of these countries (paragraph 204 of TS-R-1).
Type B(M) packages have to meet all the requirements for Type B(U) packages given above, except that different conditions may be assumed relating to: the ambient temperature;
the solar insolation; the enhanced water immersion test for packages containing a very high activity; the presence of filters or pressure relief system (and intermittent venting); the maximum normal operating pressure; the presence of LDM; and the temperature on the outer surfaces of the package. Apart from these relaxations, the requirements for Type B(U) packages must be met as far as practicable (paragraphs 665 and 666 of TS-R-1).
8.8.3. Design considerations 8.8.3.1. General
The concept of a Type B(U) or Type B(M) package is that it should be capable of withstanding most accident conditions without breach of its containment or without an excessive increase in radiation levels. Therefore, the requirements for such a package are primarily:
- Provision to enable internal generated heat to escape;
- Containment of the radioactive material contents to a high and verifiable standard before and after the tests;
- Shielding to limit the external dose rate level, before and after the tests;
- Provisions to ensure criticality safety. The package must be sub-critical with the package conditions that result in the maximum neutron multiplication consistent with:
- Routine conditions of transport (incident free);
- Normal conditions of transport tests; and
- Normal conditions of transport test followed by the accident conditions of transport test.
- Mechanical integrity to ensure survival of the drop tests;
- Provisions to ensure survival of the packaging in the thermal test (fire test);
- Ability to avoid leakage from the water pressure of the 15 m immersion test; and, - Ability to avoid rupture when exposed to the water pressure of the 200 m immersion
The contents of Type B packages come in a multiplicity of forms, radionuclide compositions, and activities. Clearly, the contents will dictate the package design. The use of the contents may also affect the design. Other design considerations, which are unrelated to the radiological safety of the consignment, include such things as excessive temperature build-up, operational interfaces with both facilities and conveyances, and maintenance.
Type B packages are designed to carry specific contents, and often are designed for carriage by specific transport modes. The Regulations specify the requirements, but do not emphasize that these requirements have to be taken into account at an early design stage and reviewed throughout the design process. The following discussion partly relates to the requirements of the Regulations but also gives advice on the best way to ensure that new package designs meet these requirements.
8.8.3.2. Design for the Regulations
Design must be carried out with the Regulations in mind. This means either having a design team specializing in transport packages or contracting specialists at an early design stage and at regular intervals. Although this may be fairly obvious, it is sometimes ignored and licensing staffs are asked to give approval for a design that falls short of the regulatory requirements. In extreme cases, packagings may sometimes be manufactured before regulatory considerations are taken into account.
8.8.3.3. Design for simplicity
Simplicity is desirable because the packagings must function over a long period with minimum operational controls. This is not a regulatory requirement but could certainly affect the ease with which the package design is approved. It is a good philosophy to design so those problems of approval are minimized. For example, stressed items should be designed so that stresses can be readily calculated. This saves effort in making a safety case. The same is true for the thermal design.
Only where a number of high-cost packagings are to be manufactured will the total project cost warrant “fine-tuning” development work to avoid over-designing the package.
8.8.3.4. Design for safety
The design should be as fail-safe as possible, considering the potential for human error. For example, safety features should be incorporated that make it unlikely for a package to be shipped without being appropriately sealed, or that an unsuspecting person can open the package and become exposed to radiation.
8.8.3.5. Design for operation
The design of any package should consider how the package is to be operated. Issues that should be addressed include:
- How the packaging will be loaded with its contents;
- How the packaging will be sealed;
- How contamination on the package surfaces will be minimized, and if such contamination should occur, how it will be removed to satisfy the requirements of the Regulations (paragraph 508 of TS-R-1);
- How the package will be handled within the facilities where it is intended to be used;
- How the package will be stowed on its conveyance;
- What steps are to be taken to minimize the likelihood of contamination of the conveyance and to ensure that any contamination that might occur will remain within the limits specified in paragraphs 512 and 513 of TS-R-1; and,
- How workers will be involved in these operations to ensure that their exposures to penetrating radiation and to contamination are kept low.
8.8.3.6. Design for Quality Assurance (QA)
The complete requirements for controlling the quality of manufacture and operation must be established at the design stage. Quality Assurance applies to all package designs, but usually the level of the QA programme is more comprehensive for packages requiring Competent Authority approval (i.e. the QA programme may follow the graded approach philosophy [3]).
The Regulations require that safety should be in the package design and not in the operational controls. QA operating procedures are required, but the package should be designed to have minimum special operating instructions. There should be nothing that can go wrong because of human error or unintentional actions.
Specifications for materials and manufacturing processes, and manufacturing tests such as those for radiation shielding, leak tightness, and operating temperature range must be written at the design stage. These specifications form an important part of the application for approval to the Competent Authority. They will be referred to either directly, or indirectly, in the certificate of approval.
The specifications should be written early in the design as they may affect fundamental features of the design, such as the need for the inclusion of double O-ring seals, for example.
The level of QA will depend on the particular package. Small packages made from commercially available items (e.g. drums) require minimum QA, except for assurance that the supplier has not changed the design of the component.
Package designs incorporating a sealing system require formal test procedures both at the stage of manufacture (paragraph 501 of TS-R-1) and before each shipment (paragraph 502 of TS-R-1). Larger packages are likely to have many features that require formal assurance.
These include seals, closure studs, shielding, neutron absorbers, thermal insulation, shock absorbers, lifting, and tie-down points.
8.8.3.7. Design for pre-shipment inspection
Pre-shipment inspection and maintenance requirements (paragraph 502 of TS-R-1) should be taken into account during the design stages:
- Designing the package to facilitate verification of the sealing of its containment system;
- Satisfaction of external radiation level requirements (e.g. see paragraphs 526, 530–
532, 572, 574, and 578 of TS-R-1);
- Satisfaction of temperature-related requirements (e.g. see paragraphs 617 and 652 of TS-R-1);
- Surface decontamination that may be required is especially important. For example,
8.8.3.8. Design for maintenance
The design should take into account the effect of maintenance on approval certification. A repair may invalidate the approval (e.g. the use of studs in place of bolts). For items likely to require repair or replacement at maintenance (e.g. screw threads), approved repair procedures should be developed at the design stage.
8.8.3.9. Design for manufacture of packaging
If all the above specifications and procedures are developed during the design stage, fabrication should proceed smoothly under an adequate QA system. Manufacturing problems should be minimal because the potential problem areas will have been covered at the design stage.
8.8.4. Examples
These requirements result in Type B(U) or Type B(M) packages that come in an extensive array of shapes and sizes. This is shown pictorially in Figure 8.9. One common design used for shipping isotopes is shown in Figure 8.10. It is important to remember that the physical size of Type B packages provides no indication of the amount of radioactivity contained. Some small Type B packages may contain very large quantities of radioactivity.
Some large Type B packages may contain relatively small quantities of radioactivity.
8.8.4.1. Fuel sample flasks
A fuel sample flask, or post-irradiation examination flask, is normally used to transport either a small number of intact fuel pins, fuel elements, or cut fuel specimens. Its purpose is to transport samples of fuel from a reactor to a laboratory for detailed metallurgical and chemical examination.
FIG. 8.8. Typical forms of Type B packages.
FIG. 8.9. Typical design of Type B(U) isotope package.
While the samples might be collected from the reactor site pond, and the flask loaded under water, they are quite often transported dry. This is because on arrival at the laboratory, the contents have to be transferred into a shielded cell for work on the fuel to be carried out Nevertheless, it may be necessary to transport the samples wet in order to limit their temperature. It is particularly important to avoid temperatures higher than those reached during operation in the reactor. This will prevent any metallurgical change in the structure of the sample between the reactor and the laboratory.
Transferring the samples into a hot cell can only be carried out from a flask that is equipped with a door. Generally, the door is an integral part of the flask and travels with it, but it is possible to design a flask in which the door travels separately from the flask. Other designs include a door that remains at the site for fitting to the flask when required, or is permanently fitted to the cell, or cave transfer port. While it may be a necessary feature of the fuel sample flask design, the door arrangement does introduce an area of potential structural weakness into the flask design. This is one good reason for having a detachable door that does not travel as part of the flask.
Fuel sample flasks tend to be designed for specific facilities. This in itself can dictate the form that a design will take. For example, where crane capacity within a building is limited, this may automatically mean that lead, rather than steel, has to be used as the shielding material in order to keep the weight down. This has the subsequent effect of dictating the consideration in the package design of the behaviour of the lead under the thermal accident test condition and may require an insulating thermal shield to protect the lead. However, the thermal shield may also need to be separable from the flask, because the combination of the two would be too heavy to handle within the facility. Many of these
In facilities where weight handling is not a problem, the shielding material may be specified as steel, or a thick steel/lead combination. The presence of a door in the design is still a structurally weakening feature and this may result in a design requirement to provide impact limiters at each end of the flask for protection. Although there is not a threat of the radiation shield melting, the penetration seals may be threatened by the high temperatures resulting from the thermal test. This can be alleviated by providing thermal shields as part of the impact limiters.
As far as possible, it is desirable at all times to prevent the inside as well as the outside of the flask from becoming contaminated. This ensures that the contents are contained within a can or drum before loading into the flask. The leak-tightness of the can cannot normally be checked before shipment, because of the high radiation dose rate from the can. However, in practice, it provides a further containment barrier and keeps the flask contamination to a minimum.
8.8.4.2. Irradiated nuclear fuel and high level waste flasks
One of the major types of Type B packagings are those used for the transport of irradiated nuclear fuel. These flasks are discussed in detail in paragraph 8.9.3.1 of this chapter. In addition, during the discussion of LSA material, several types of waste packages were mentioned. Not all wastes can be qualified as LSA material. Some intermediate and high level wastes need to be transported in Type B packages rather than in industrial packages.
Typical Type B(U) irradiated nuclear fuel packages are shown in Figures 8.10. and 8.11.
FIG. 8.10. Type B(U) irradiated Magnox nuclear fuel package.
FIG. 8.11. Type B(U) irradiated LWR nuclear fuel package.
8.8.4.3. High enriched fissile material packages
Other, specialized Type B packages addressing fissile materials are those designed for the carriage of highly enriched products such as plutonium oxide powders. Here the emphasis is on high integrity seals, high integrity containment and high structural integrity. The quantity of material carried tends to be small; therefore, the sealed enclosures tend to be small in volume. In addition, users take great care to ensure that this material is transported with the highest degree of safety. A number of designs have been free-drop tested (in addition to the regulatory requirements) from heights of 300 m, 600 m and 1600 m with no dispersal of contents being recorded.
8.8.4.4. Transuranic waste packages
Type B packages have been designed for the transport of transuranic (TRU) wastes.
These packages are different from irradiated nuclear fuel and high level waste packages because they generally are not required to have much, if any, gamma shielding. As such, they tend to be large, lighter weight packagings, and do not have the thick layers of steel, lead or depleted uranium. Since most of the radionuclides present in such wastes are alpha-emitters, the structure of the packagings required to resist the normal and accident conditions of transport are usually sufficient to provide all the shielding necessary to satisfy the external radiation level requirements of the Regulations.
8.8.5. Approvals
8.8.5.1. Unilateral and multilateral approval of package designs
Each Type B(U) package design requires unilateral approval (paragraphs 802 and 806 of TS-R-1), except that:
- A package design for fissile material requires multilateral approval; and,
- A Type B(U) package design for low dispersible radioactive material also requires multilateral approval.
Unilateral approval of a design, (paragraph 205 of TS-R-1), means that the approval must be given by the Competent Authority of the country of origin of the design only.
Each type B(M) package design, including those for fissile and those for low dispersible radioactive material requires multilateral approval (paragraphs 802 and 809 of TS-R-1).
Multilateral approval of a design (paragraph 204 of TS-R-1) means approval by the relevant Competent Authority both of the country of origin of the design, or shipment, and of each country through or into which the consignment is to be transported. The term “through or into” specifically excludes “over”. This means that the approval and notification requirements do not apply to a country over which radioactive material is carried in an aircraft, provided that there is no scheduled stop in that country.
8.8.5.2. Approval application contents
Each application for a Type B(U) or a Type B(M) package design approval to a Competent Authority needs to include (paragraph 807 of TS-R-1):
- A detailed description of the proposed radioactive contents with reference to their physical and chemical states and the nature of the radiation emitted.
- A detailed statement of the design, including complete engineering drawings and schedules of materials and methods of manufacture.
- A statement of the tests, which have been performed, and their results, or evidence based on calculation methods or other evidence that the design is adequate to meet the applicable requirements.
- The proposed operating and maintenance instructions for the use of the packaging.
- A specification of the materials of manufacture of the containment system, the samples to be taken, and the tests to be made, if the package is designed to have a maximum normal operating pressure in excess of 100 kPa gauge.
- Where the proposed radioactive contents are irradiated fuel, the applicant must state and justify any assumption in the safety analysis relating to the characteristics of the fuel and describe any pre-shipment measurement required.
- Any special stowage provisions necessary to ensure the safe dissipation of heat from the package considering the various modes of transport to be used and the type of conveyance or freight container.
- A reproducible illustration, not larger than 21 cm by 30 cm, showing the make-up of the package.
- A specification of the applicable Quality Assurance programme.
In addition to the previous required information, an application for approval of a Type B(M) package design has to include the following information (paragraph 810 of TS-R-1):
- A list of the requirements specified in paragraphs 637, 653, 654, and 657-664 of TS-R-1 with which the package does not conform. These are the conditions that relate to:
the ambient temperature; the solar insolation; the enhanced water immersion test for packages containing a very high activity; the presence of filters or pressure relief system (and intermittent venting); the maximum normal operating pressure; and the temperature on the outer surfaces of the package;
- Any proposed supplementary operational controls to be applied during transport not regularly provided for in the TS-R-1 Regulations, but which are necessary to ensure the safety of the package or to compensate for the deficiencies listed in (1) above;
- A statement relative to any restrictions on the mode of transport and to any special loading, carriage, unloading or handling procedures; and,
- The range of ambient conditions (temperature, solar radiation) which will probably be encountered during transport and which have been taken into account in the design.
8.8.5.3. Approval certificate
Once it is satisfied that the package design meets the requirements, the Competent Authority establishes an approval certificate (paragraph 827 of TS-R-1). This states that the approved design meets the applicable requirements for Type B(U) or Type B(M) package, as applicable, and assigns a unique identification mark to that design.
Each approval certificate for package design that is issued by a Competent Authority must include the following information (paragraph 833 of TS-R-1):
- The type of certificate.
- The Competent Authority identification mark.
- The issue date and an expiry date.
- Any restriction on the modes of transport, if appropriate.
- A list of applicable national and international regulations, including which edition of the IAEA Regulations for the Safe Transport of Radioactive Material the design is to be approved.
- The following statement, “This certificate does not relieve the consignor from compliance with any requirement of the government of any country through or into which the package will be transported”.
- References to certificates for alternative radioactive contents, other Competent Authority validation, or additional technical data for information, as deemed appropriate by the Competent Authority.
- A statement authorizing shipment where shipment approval is required, if deemed appropriate.
- Identification of the packaging.
- A description of the packaging by a reference to the drawings or specification of the design. If deemed appropriate by the Competent Authority, a reproducible illustration, not larger than 21 cm by 30 cm, showing the make-up of the package should also be provided. This should be accompanied by a brief description of the packaging, including materials of manufacture, gross mass, general outside dimensions, and