Depleted uranium hexafluoride (DUHF; also referred to as depleted uranium tails, depleted uranium tailings or DUF6) is a byproduct of the processing of uranium hexafluoride into enriched uranium. It is one of the chemical forms of depleted uranium (up to 73-75%), along with depleted triuranium octoxide (up to 25%) and depleted uranium metal (up to 2%). DUHF is 1.7 times less radioactive than uranium hexafluoride and natural uranium.
History
The concept of depleted and enriched uranium emerged nearly 150 years after the discovery of uranium by Martin Klaproth in 1789. In 1938, two German physicists Otto Hahn and Fritz Strassmann had made the discovery of the fission of the atomic nucleus of the 235U isotope, which was theoretically substantiated by Lise Meitner, Otto Robert Frisch and in parallel with them Gottfried von Droste and Siegfried Flügge. This discovery marked the beginning of the peaceful and military use of the intra-atomic energy of uranium. A year later, Yulii Khariton and Yakov Zeldovich were the first to prove theoretically that with an insignificant enrichment of natural uranium in the 235U isotope, it is possible to give the process a chain character, creating the necessary conditions for the continuous fission of atomic nuclei. The principle of a nuclear chain reaction implies that at least one neutron, during the decay of an atom of the isotope 235U, will be captured by another atom of 235U and, accordingly, will also cause its decay. In this process, the probability of such a "capture" plays a significant role. To increase this probability, a fractional increase in the 235U isotope is necessary, which in natural uranium constitutes only 0.72%, along with the primary 238U, which takes up 99.27% and 234U - 0.0055%, respectively. A small fraction of the 235U isotope content in natural uranium, when used as a primary fissile material in most areas of nuclear technology, necessitated enrichment of natural uranium in this isotope.
Over time, in the process of improving nuclear technologies, optimal technological and economic solutions were identified, requiring an increase in the 235U fraction, that is, uranium enrichment and, as a consequence of these processes, the appearance of an equivalent amount of depleted uranium with a 235U isotope content of less than 0.72%. The content of 235U in the depleted uranium formed during the enrichment process depends on the purpose of the enrichment.
Competition
By the mid-1960s, the United States had a monopoly on the supply of uranium fuel for Western nuclear power plants. In 1968, the USSR declared its readiness to accept orders for uranium enrichment. As a result, a new competitive market began to form in the world, and new commercial enrichment companies began to appear (URENCO and Eurodif). In 1971, the first Soviet contract was signed with the French Alternative Energies and Atomic Energy Commission, where nuclear power plants were actively built. In 1973, roughly 10 long-term contracts were signed with power companies from Italy, Germany, Great Britain, Spain, Sweden, Finland, Belgium and Switzerland. By 2017, large commercial enrichment plants have been operating in France, Germany, the Netherlands, Great Britain, the United States, Russia and China. The development of the enrichment market has led to the accumulation of over 2 million tons of DUHF in the world during this period.
Terminology
Since the discovery of uranium and its properties, some terms such as Q-metal, depletalloy, or D-38 have become obsolete, and new terms have replaced them. DUHF can be referred to as depleted uranium (DU), and likewise, depleted uranium is sometimes referred to as uranium hexafluoride (UF6). However, all three terms have significant differences between them, not only in their isotopic composition (that is DUHF being a product of the processed uranium hexafluoride), but also in the understanding of the whole and the constituent parts. Depleted uranium, as a whole concept, may exist in several chemical forms; in the form of DUHF, the most common form, with a density of 5.09 g/cm3, in the form of depleted triuranium octoxide with a density of 8.38 g/cm3, and in the form of depleted uranium metal with a density of 19.01 g/cm3.