Nuclear fission uranium production

While the separations at Oak Ridge were mostly of a physical nature, dependent upon differences in atomic or molecular masses, separations at the Hanford site were mostly chemical in nature. Bombardment of uranium with neutrons produced Pu 239, a mixture of lighter metals, notably rare earths, created as nuclear fission by-products, and unchanged uranium. One consequence of the Hanford operation was the development of ion-exchange chromatography as a major purification and analytical method to separate the rare earths. It would become a general technique for separating ionic substances. 

Uranium is converted by CIF, BiF, and BrP to UF. The recovery of uranium from irradiated fuels has been the subject of numerous and extensive investigations sponsored by atomic energy agencies in a number of countries (55—63). The fluorides of the nuclear fission products are nonvolatile hence the volatile UF can be removed by distiUation (see Nuclearreactors Uraniumand uranium compounds). 

Economic Aspects. The principal market for deuterium has been as a moderator for nuclear fission reactors fueled by unenriched uranium. The decline in nuclear reactor constmetion has sharply reduced the demand for heavy water. The United States has stopped large-scale production of D2O, and Canada is the only suppHer of heavy water at this time. Heavy water is priced as a fine chemical, and its price is not subject to market forces. 

The only large-scale use of deuterium in industry is as a moderator, in the form of D2O, for nuclear reactors. Because of its favorable slowing-down properties and its small capture cross section for neutrons, deuterium moderation permits the use of uranium containing the natural abundance of uranium-235, thus avoiding an isotope enrichment step in the preparation of reactor fuel. Heavy water-moderated thermal neutron reactors fueled with uranium-233 and surrounded with a natural thorium blanket offer the prospect of successful fuel breeding, ie, production of greater amounts of (by neutron capture in thorium) than are consumed by nuclear fission in the operation of the reactor. The advantages of heavy water-moderated reactors are difficult to assess. 

Production in Fission of Heavy Elements. Tritium is produced as a minor product of nuclear fission (47). The yield of tritium is one to two atoms in 10,000 fissions of natural uranium, enriched uranium, or a mixture of transuranium nucHdes (see Actinides and transactinides Uranium). 

In 1938 Niels Bohr had brought the astounding news from Europe that the radiochemists Otto Hahn and Fritz Strassmann in Berlin had conclusively demonstrated that one of the products of the bom-bardmeiit of uranium by neutrons was barium, with atomic number 56, in the middle of the periodic table of elements. He also announced that in Stockholm Lise Meitner and her nephew Otto Frisch had proposed a theory to explain what they called nuclear fission, the splitting of a uranium nucleus under neutron bombardment into two pieces, each with a mass roughly equal to half the mass of the uranium nucleus. The products of Fermi s neutron bombardment of uranium back in Rome had therefore not been transuranic elements, but radioactive isotopes of known elements from the middle of the periodic table. 

At the end of 1938, Hahn sent her a description of his experiments on the interaction of neutrons with uranium. He and a young chemist. Fritz Strasstnan. had detennined that one of the reaction products was clearly barium. Meitner was so excited about this that she showed Hahn s letter to her nephew, physicist Otto Frisch. Their discussions on the topic gave birth to the idea of nuclear fission. 

Nuclear fission is a process in which a heavy nucleus—usually one with a nucleon number of two hundred or more—separates into two nuclei. Usually the division liberates neutrons and electromagnetic radiation and releases a substantial amount of energy. The discoveiyi of nuclear fission is credited to Otto I lahn and Fritz Strassman. In the process of bombarding uranium with neutrons in the late 1930s, they detected several nuclear products of significantly smaller mass than uranium, one of which was identified as Ba. The theorectical underpinnings that exist to this day for nuclear fission were proposed by Lise Meitner and Otto Frisch. Shortly after Hahn and Strassman s discovery. 

Fluidized-bed CVD was developed in the late 1950s for a specific application the coating of nuclear-fuel particles for high temperature gas-cooled reactors. PI The particles are uranium-thorium carbide coated with pyrolytic carbon and silicon carbide for the purpose of containing the products of nuclear fission. The carbon is obtained from the decomposition of propane (C3H8) or propylene... 

Technetium then became available in a weighable quantity because of uranium nuclear fission leading to the production of "Tc in nuclear reactors. The total amount of "Tc in the world at the end of 1993 is estimated to be 78 tons, more abundant than rhenium on the earth. 

The development of chemistry itself has progressed significantly by analytical findings over several centuries. Fundamental knowledge of general chemistry is based on analytical studies, the laws of simple and multiple proportions as well as the law of mass action. Most of the chemical elements have been discovered by the application of analytical chemistry, at first by means of chemical methods, but in the last 150 years mainly by physical methods. Especially spectacular were the spectroscopic discoveries of rubidium and caesium by Bunsen and Kirchhoff, indium by Reich and Richter, helium by Janssen, Lockyer, and Frankland, and rhenium by Noddack and Tacke. Also, nuclear fission became evident as Hahn and Strassmann carefully analyzed the products of neutron-bombarded uranium. 

The production of 10 TW of nuclear power with the available nuclear fission technology will require the construction of a new 1 GWe nuclear fission plant every day for the next 50 years. If this level of deployment would be reached, the known terrestrial uranium resources will be depleted in 10 years [3], Breeder reactor technology should be developed and used. Fusion nuclear power could give an inexhaustible energy source, but currently no exploitable fusion technology is available and the related technological issues are extremely hard to solve. 

It is found in ores such as monazite, gadohnite, and bastnasite. It was first separated into three elements in 1843 (yttria, erbia, and terbia). Erbium is also produced as a by-product of nuclear fission of uranium. 

As mentioned, protactinium is one of the rarest elements in existence. Although protactinium was isolated, studied, and identified in 1934, little is known about its chemical and physical properties since only a small amount of the metal was produced. Its major source is the fission by-product of uranium found in the ore pitchblende, and only about 350 milligrams can be extracted from each ton of high-grade uranium ore. Protactinium can also be produced by the submission of samples of throrium-230 (g Th) to radiation in nuclear reactors or particle accelerators, where one proton and one or more neutrons are added to each thorium atom, thus changing element 90 to element 91. 

Low-Level Waste. Low-level wastes are further divided into categories of special nuclear material, source material, and byproduct material, depending on the isotopes contained. Special nuclear material refers to uranium 233, plutonium 239, and uranium containing more than the natural abundance of uranium 235. Source material refers to materials containing 0.05 percent or more of thorium or uranium in any physical or chemical form except that covered under special nuclear material. By-product materials consist of all other radioactive materials including fission and activation products. 

The first scientific attempts to prepare the elements beyond uranium were performed by Enrico Fermi, Emilio Segre, and co-workers in Rome in 1934, shortly after the existence of the neutron was discovered. This group of investigators irradiated uranium with slow neutrons and found several radioactive products, which were thought to be due to new elements. However, detailed chemical studies by Otto Hahn and Fritz Strassman in Berlin showed these species were isotopes of the known elements created by the fission of uranium into two approximately equal parts (see Chap. 11). This discovery of nuclear fission in December of 1938 was thus a by-product of man s quest for the transuranium elements. 

The discovery of fission was a complete surprise and also a great shock, because it shattered fundamental ideas of nuclear behavior that had guided the investigation. The surprise was evident in the events of December 1938. On December 10, Enrico Fermi was awarded the Nobel Prize in physics. He and his group in Rome had been the first to irradiate uranium with neutrons and to propose that transuranium elements had been formed in the process. In his Nobel lecture, Fermi was so confident of the first two, elements 93 and 94, that he referred to them by name ausonium and hesperium. But at that very moment, the Berlin team of Otto Hahn, Lise Meitner, and Fritz Strafimann was on the verge of identifying barium among the uranium products. By the end of the year, they understood that uranium had split, explained the fission process, and concluded that the transuranium elements were false. When Fermi published his Nobel lecture, he added a footnote to that effect, but by then ausonium and hesperium were themselves footnotes (if that) in the history of science. [1]... 

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