Transportation of Depleted Uranium Materials in Support of the Depleted Uranium Hexafluoride Conversion Program
Issues associated with transport of depleted UF6 cylinders and conversion products.
Conversion Plan Transportation Requirements
The DOE has prepared two Environmental Impact Statements (EISs) for the proposal to build and operate depleted uranium hexafluoride (UF6) conversion facilities at its Portsmouth and Paducah gaseous diffusion plant sites, pursuant to the National Environmental Policy Act (NEPA). The proposed action calls for transporting the cylinder at ETTP to Portsmouth for conversion. The transportation of depleted UF6 cylinders and of the depleted uranium conversion products following conversion was addressed in the EISs.
Shipment of Radioactive Materials
Under the Department of Transportation Act of 1966, the U.S. Department of Transportation (DOT) has regulatory responsibility for safety in transportation of all hazardous materials, including radioactive material. DOT developed a single a set of safety standards that assured that properly prepared shipments of hazardous materials would be acceptable for transport by all modes (rail, highway, air, and water). These standards are set forth primarily in DOT's Hazardous Materials Regulations (HMR) located in 49 CFR Parts 100 - 178.
Under the Atomic Energy Act of 1954, as amended, the U.S. Nuclear Regulatory Commission (NRC) also has responsibility for safety in the transport of radioactive materials. Due to the overlap in statutory authorities of the NRC and DOT, the two agencies have a Memorandum of Understanding (MOU) with regard to regulation of the transport of radioactive material. Consistent with the MOU, the NRC has promulgated, in 10 CFR Part 71, shipping requirements for radioactive materials.
The primary regulatory approach used by DOT and NRC for ensuring safety during transportation of radioactive materials is by specifying standards for the proper packaging of such materials. Packaging for transporting radioactive materials must be designed, constructed, and maintained to ensure that they will contain and shield their contents during normal transportation. The type of packaging used is determined by the radioactive hazard associated with the packaged material. The hazard is determined by the characteristics of the specific radioactive material and its physical form (e.g., solid, liquid, or gas). The regulations also specify many requirements for labeling, marking, training, and administrative controls.
The shipment of radioactive materials may take place by truck, rail, or barge. Federal regulations do not place route restrictions on the movement of depleted UF6 cylinders or depleted uranium on United States highways or railroads.
It should be noted that the nuclear properties of depleted uranium are such that the occurrence of a nuclear criticality (i.e., a nuclear chain reaction) is not a concern, regardless of the amount of depleted uranium present. However, criticality is a concern for the handling, packaging, and shipping of enriched uranium. For enriched uranium, criticality control is accomplished by employing, individually or collectively, specific limits on uranium-235 enrichment, mass, volume, geometry, moderation, and spacing for each type of package. The amount of uranium that may be contained in an individual package and the total number of packages that may be transported together are determined by the nuclear properties of the enriched uranium.
Shipment of Depleted UF6 Cylinders
UF6 has been transported safely for more than 40 years. Specific requirements exist for the shipment of UF6 cylinders. Among other things, UF6 cylinders must be designed, fabricated, inspected, tested, and marked in accordance with the version of American National Standard N14.1, "Uranium Hexafluoride - Packaging for Transport" that was in effect at the time the cylinder was manufactured. Although a detailed discussion of depleted UF6 transportation regulations is not included here, three requirements are particularly important relative to depleted UF6 cylinder shipments: (1) cylinders must be filled to less than 62% of the certified volumetric capacity (the fill-limit was reduced to 62% from 64% around 1987); (2) the pressure within cylinders must be less than 14.8 psia; and (3) cylinders must be free of cracks, excessive distortion, bent or broken valves or plugs, and broken or torn stiffening rings or skirts, and must not have shell thicknesses that have decreased below a specified minimum value. Cylinders not meeting these requirements are often referred to as substandard or noncompliant.
Although the exact number is not yet known, preliminary reports suggest that many of the cylinders at ETTP will not meet the DOT transportation requirements. Three options exist for shipping these noncompliant cylinders:
- The UF6 contents could be transferred from noncompliant cylinders into new or compliant cylinders.
- An exemption could be obtained from the DOT, allowing the UF6 cylinder to be transported either "as is" or following repairs. The primary finding that DOT must make to justify granting an application for an exemption is that the proposed alternative will achieve a level of safety that either: (1) is at least equal to the level of safety required by the otherwise applicable regulation; or, (2) if the otherwise applicable regulations do not establish a required level of safety, is consistent with the public interest and will adequately protect against the risks to life and property inherent in the transportation of hazardous materials in commerce.
- Noncompliant cylinders could be shipped in an "overpack." In this case, the shipper would have to obtain an exemption from DOT allowing the existing cylinder, regardless of its condition, to be transported if it is placed into a metal overpack. The metal overpack would have to be specially designed. Furthermore, DOT would have to determine that, if the overpack is fabricated, inspected, and marked according to its design, the resulting packaging (including the cylinder and the overpack) would have a level of safety at least equal to the level of safety required for a new UF6 cylinder.
Shipment of Depleted Uranium Conversion Products
The depleted uranium conversion product will be shipped as low specific activity, group I, (LSA-I) material. All LSA materials have a characteristic of presenting limited radiation hazard, because of their relatively low concentration of radioactivity.
Evaluation of Transportation Risks
The EISs for the conversion project include a detailed evaluation of the risks associated with the transportation of the depleted uranium materials. This assessment includes the risks to both workers and members of the public during normal transportation conditions and hypothetical accidents.
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