Requirements for packages containing fissile material

The requirements for packages containing fissile material are additional requirements imposed to ensure that packages with fissile material contents will remain subcritical under normal and accident conditions of transport AU other relevant requirements of the Regulations must be met. The systan for implonenting criticality control in transport is prescribed in Section V of the Regulations. 

Packages containing fissile material are required to be designed and transported in such a way that an accidental criticaUty is avoided. Criticality is achieved when the fission chain reactions become self-supported due to the balance between 

Neutron absorbers are sometimes employed in the packaging to reduce the effect of moderation and the contribution to the neutron multiplication resulting from interaction among packages (see para. 501.8). Typical neutron absorbing materials used for criticality control are most effective when a neutron moderator is present 

The effects of temperature changes (para. 671(a)(vi)) on the stability of fissile material form or on the neutron interaction properties are required to be examined. For example, uranium systems dominated by very low energy (thermal) neutrons have an increase in neuUon multiphcation as the temperature is reduced. Temperature changes may also influence the package integrity. The temperatures which should be considered include those resulting from ambient condition requirements specified in para. 676 and those of the tests (paras 728 or 736, as appropriate). 

Exceptions from the requirements for packages containing fissile material 

Fissile material meeting one of the provisions (a)-(d) of this paragraph is excepted from the requirement to be transported in packages that comply with paras 673-682 as well as the other requirements of these Regulations that apply to fissile material. Only one type of exception is allowed per consignment  

Neither beryllium nor deuterium shall be present in quantities exceeding 1% of the applicable consignment mass limits provided in Table 12, except for deuterium in natural concentration in hydrogen. 

TABLE 12. CONSIGNMENT MASS LIMITS FOR EXCEPTIONS FROM THE REOUIREMENTS FOR PACKAGES CONTAINING FISSILE MATERIAL 

Fissile material mass (g) Fissile material mass (g) 

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Vn.l. This appendix offers general advice on the demonstration of compliance with the requirements for packages containing fissile material set forth in paras 671 to 682 of the Regulations. Performance and documentation of a thorough criticality safety assessment provides the demonstration of compliance called for in these paragraphs. The documentation of the criticality safety assessment included in a Safety Assessment Report (SAR) is an essential part of the application for approval to the competent authority. This criticality safety assessment should be performed by the application of suitable quality assurance procedures at aU stages as prescribed in para. 813. 

For packages containing fissile material, it shall be determined whether the assumptions and conditions used in the assessments required by paras 671-682 for one or more packages are valid. 

If the radioactive contents are fissile material which is not excepted from the requirements for packages containing/wiife material, then the approval requirements in paras 812 and 820 of the Regulations shall additionally apply. 

The approval certificate should identify any requirements for closure of a package containing fissile material which are necessary as a result of the assumptions made in the criticality safety assessment relative to water in-leakage for a single package in isolation (see para. 677). Inspections and/or tests should be made to ascertain that any special features for prevention of water in-leakage have been met. 

Packages containing fissile material which meet any of the requirements in paras 672(a)-(d) are excepted from the criticality safety assessment specified in para. 671(b). Assurance that the excepted criteria are met for both the individual package and the consignment is the responsibility of the consignor of the excepted material. 

Each requirement in para. 820 should be applied separately. For example, a consignment of a vented Type B(M) package containing fissile material may need a shipment approval according to both paras 820(a) and 820(c). 

Prevention of criticality in arrays of waste packages containing fissile materials can be obtained both in operational and post-closure periods by safe geometry arrangements of waste packages and engineered barriers. In certain cases it will be necessary to add site decide requirements on nuclide concentration. Sub-criticality must be ensured for any water content and distribution. 

Each package design for fissile material which is not excepted according to para. 672 from the requirements that apply specifically to packages containing fissile material shall require multilateral approval. 

The leaktightness requirement for a containment system in a Type B(U), Type B(M) or Type C package depends on the radiotoxicity of the radioactive contents for example, a Type B(U) or Type C package under accident conditions must have the release limited to a value of in the period of a week. This connection to the A2 value means that for highly toxic radionuclides such as plutonium and americium the allowable volumetric leak rate will be much lower than for low enriched uranium. However, if fissile material is able to escape from the contaimnent system under accident conditions, it must be demonstrated that the quantity that escapes is consistent with that assumed in the criticality safety assessment in applying para. 682(c). 

Regarding the requirement for competent authority approval for packages designed to contain fissile material, it is noted that para. 672 excludes certain packages from those requirements that apply specifically to fissile material. However, all relevant requirements that apply to the radioactive, non-fissile properties of the package contents still apply. 

Paragraph 682(c) provides a severe restriction on any fissile material permitted to escape the package under accident conditions. All precautions to preclude the release of fissile material from the containment system should be taken. The variety of configurations possible for fissile material escaping from the containment system and the possibility of subsequent chanical or physical changes require that the total quantity of fissile material that escapes from the array of packages should be less than the minimum critical mass for the fissile material type and with optimum moderator conditions and reflection by 20 cm of full density water. An equal amount of... 

Packages designed to contain uranium hexafluoride shall meet the requirements prescribed elsewhere in these Regulations which pertain to the radioactive and fissile properties of the material. Except as allowed in para. 632, uranium hexafluoride in quantities of 0.1 kg or more shall also be packaged and transported in accordance with the provisions of the International Organization for Standardization document ISO 7195 Packaging of Uranium Hexafluoride (UF ) for Transport [10], and the requirements of paras 630-631. 

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