440 nuclear power reactors operate across the globe. 96 are in the United States, where they produce nearly 20% of the electricity generated throughout the nation. An assemblage of standards assure that nuclear power plants operate efficiently and safely. By driving the nuclear fuel cycle, ANSI N14.1-2019: Nuclear Materials – Uranium Hexafluoride – Packagings For Transport plays an integral role in the production of nuclear energy.
What is Uranium Hexafluoride (UF6)
Uranium Hexafluoride (UF6), or “hex,” is the key chemical used in the conversion and enrichment of nuclear fuel. Consisting of one atom of uranium and six atoms of fluorine, this molecule, in solid form, is a white, crystalline material resembling rock salt. However, within a range of temperature and pressure, it can be a solid, liquid, or gas. In fact, its various states of matter contain unique properties that make it incredibly convenient for uranium processing.
UF6, which is specified in ANSI N14.1-2019, plays a pivotal role in the production cycle of nuclear fuel.
Nuclear Fuel Cycle
The narrative of nuclear energy production neither begins nor ends with UF6.
Instead, the nuclear fuel cycle commences with uranium in the earth’s crust. As a radioactive metal, uranium is found in most rocks and soils. Once mined, the process of milling extracts uranium from the ore, resulting in a uranium oxide concentrate occasionally referred to as “yellowcake.”
Since only 0.7% of natural uranium is fissile—capable of undergoing fission—milled uranium oxide needs to be converted to uranium hexafluoride. This takes place at a conversion facility, where the uranium oxide is combined with anhydrous hydrogen fluoride and fluorine gas. This series of chemical reactions forms UF6. The hex is placed into steel cylinders and shipped as a solid to a gaseous diffusion plant for enrichment (this is where ANSI N14.1-2019 supports the industry). Once enriched, the uranium hexafluoride is reconverted to enriched uranium oxide.
Nuclear fuel consists of this enriched uranium oxide, pressed and sintered at temperatures over 1400°C. These pellets are stacked together and sealed in fuel rods. Over 200 rods are bundled together to form a fuel assembly, and a couple hundred of these assemblies comprise a reactor core. Inside the nuclear reactor, during the fission process, heat is released and the fuel rods are immersed in water. The heat created by fission turns the water into steam, spinning a turbine and thereby producing electricity.
While the operation of nuclear power plants does not emit greenhouse gases, the various other steps do lead to emissions, so nuclear energy is considered low-carbon.
The ANSI N14.1-2019 American National Standard
To provide for compatibility of UF6 packagings among different users throughout the nuclear industry, ANSI N14.1-2019 covers a range of needs. This includes quality assurance, design and fabrication requirements, testing, marking, and standard diameters and volumes. The standard also covers cylinder loadings, shipping requirements, and requirements for valves, plugs, and valve protectors.
Developed by the Accredited Standards Committee on Packaging and Transport of Radioactive and Non-Nuclear Hazardous Materials, N14, the secretariat of which is the Institute for Nuclear Materials Management (INMM), ANSI N14.1-2019 covers specific requirements for the procurement of new UF6 packagings for transportation of 0.2205 lb (0.1 kg) or more of UF6. However, other requirements in the standard do apply to in-service packagings, including those for inspections, cleanliness (impurities can result in serious explosions), and maintenance.
ANSI N14.1-2019: Nuclear Materials – Uranium Hexafluoride – Packagings For Transport is available on the ANSI Webstore.
Relationship with ISO 7195
ANSI N14.1-2019, by addressing the packaging of UF6 for transport, helps assure a safe and economical nuclear industry. Regulations also help fulfill this purpose, so the standard does not take precedence over applicable U.S. Nuclear Regulatory Commission, U.S. Department of Energy, U.S. Department of Transportation, or other governmental regulations.
Since ANSI N14.1-2019 is also used for the international transportation of UF6, international transport regulations, based on IAEA SSR-6 (Regulations for the Safe Transport of Radioactive Material), can also apply. SSR-6 uses ISO 7195:2005 – Nuclear Energy – Packaging Of Uranium Hexafluoride (UF6) For Transport as a reference.
Furthermore, as noted in the Foreword of ANSI N14.1-2019:
“The [N14] Committee has participated and will continue to participate in the development and maintenance of ISO 7195.”