Uranium elements

A fuel channel in a natural uranium reactor is 5 m long and has a heat release of 0.25 MW. If the thermal conductivity of the uranium is 33 W/mK, what is the temperature difference between the surface and the centre of the uranium element, assuming that the heat release is uniform along the rod ... 

It should be noted that the ytterbium listed above was a mixture discovered in the mineral erbia by de Marignac in 1878 and not the neoytterbium/aldebaranium element renamed ytterbium that was foimd in the mineral ytterbia. The columbium was a mixture found in the mineral samarskite and was not the present day columbium/niobium. The ionium listed above was a mixture of terbium and gadolinium that was found in the mineral yttria and does not refer to °Th. Finally, the neptunium refers to material fovmd in niobium/tantalum minerals and does not refer to the 1940 discovery of the trans-uranium element produced via a neutron capture reaction on a uranium sample. 

In addition to these actinide(IV) compounds, the increasing stabihty of the - -3 oxidation state for the trans-uranium elements has recently led to the preparation of compounds of formula K[M(CgH8)2] where M=Np or Pu 31). In their chemical behavior these compounds axe similar to the corresponding lanthanide complexes vide infra) and their X-ray powder patterns suggest they have the same structure. They appear to be much more ionic than their -f4 analogues. 

McMillan, E. M., The trans-uranium elements early history, Les Prix... 

So how many elements are there I do not know, and neither does anyone else. Oh, they can tell you how many natural elements there are - how many we can expect to find at large in the universe. That series stops around uranium, element number 92. But as to how many elements are possible - well, name a number. We have no idea what the limit might be. 

The discovery of fermium (also einsteinium) was not the result of very carefully planned experiments, as in the cases of the other trans uranium elements, bill fermiuni and einsteinium were found in Ihe debris of an atomic weapon lest in the Pacific in November 1952. Researchers, using the Oak Ridge High Flux Isotope Reactor (HFIR) which produced 3.2-hour " Fm. determined ihe magnetic moment of the atomic ground state of the neutral fermium atom with a modified atomic beam magnetic resonance... 

The periodic table prepared by Mendeleev became a target for scientists and elements as the blank spaces in his table were quickly discovered. Of great importance also was the indication of the presence of the trans-uranium elements in Mendeleev s studies. 

Nuclear chemistry (radiochemistry) has now become a large and very important branch of science. Over four hundred radioactive isotopes have been made in the laboratory, whereas only about three hundred stable isotopes have been detected in nature. Three elements —technetium (43), astatine (85), and promethium (61), as well as some trans-uranium elements, seem not to occur in nature, and are available only as products of artificial transmutation. The use of radioactive isotopes as tracers has become a valuable technique in scientific and medical research. The controlled release of nuclear energy promises to lead us into a new world, in which the achievement of man is no longer limited by the supply of energy available to him. 

Manufacture of the Trans-Uranium Elements. The first transuranium element to be made was a neptunium isotope, Np . This isotope was made by E. M. McMillan and P. H. Abelson, in 1940, by bombarding uranium with high-speed deuterons ... 

Plutonium and the four heavier trans-uranium elements whose existence have been reported, americium, curium, berkelium, and californium, were discovered by Professor G. T. Seaborg and his collaborators at the University of California in Berkeley. Americium has been made as the isotope Am by the following reactions ... 

It was soon noted that iron was by no means unique in forming tt-cyclopentadienyl derivatives, and research groups in several countries set out to determine the nature and scope of cyclopentadienyl-metal chemistry. At the present time, practically all the metals of the short transition series, as well as nearly all the metals and metalloids of the main group series, form one or more cyclopentadienyl compounds. In addition, cyclo-pentadienyl derivatives of over one-half the lanthanides have now been described, and even cyclopentadienyl derivatives of U, Th, and several mns-uranium elements are known. The present status of cyclopentadienyl-metal chemistry is illustrated in part in Figure 1. Elements designated by shaded areas are known to form one or more cyclopentadienyl derivatives. 

The evidence for this supposed process came from chemical analysis. Hahn and Strassmann published a scientific paper showing that small amounts of barium (element 56) were produced when uranium (element 92) was bombarded with neutrons. It was very puzzling to them how a single neutron could transform element 92 into element 56. 

Trans-uranium elements Transition metals Gold... 

Plutonium is a member of the actinoid family. The actinoids occur in Row 7 of the periodic table. The periodic table is a chart that shows how chemical elements are related to one another. The actinoids get their name from element 89, actinium, which is sometimes considered the first member of the family. Plutonium is also called a transuranium element. The term transuranium means beyond uranium. Elements with atomic numbers greater than that of uranium (92) are called transuranium elements. 

The mutual separation of actinide elements and the selective isolation of useful actinides from fission products are indispensable for the nuclear fuel cycle and have become important subjects of investigation for the development of advanced nuclear fuel reprocessing and TRU (TRans Uranium elements) waste management [1], A variety of research concerning the separation chemistry of actinides has so far been accumulated [2]. There are, however, only a few theoretical studies on actinides in solution[3-5]. Schreckenbach et a), discussed the stability of uranyl (VI) tetrahydroxide [UO,(OH) ] [3] and Spencer and co-workers calculated the optimized structures of some uranyl and plutonyl hydrates [AcO, nH,0 (Ac = U, Pu and n = 4,5,6)] [4],... 

Some elements are not foimd in nature but are produced artificially in particle accelerators like the one shown in Figure 3.10. These are known as synthetic elements. The synthetic elements, made by means of nuclear reactions, are marked on the periodic table. They include technetium, element 43, and all the elements after uranium, element 92. Although small amounts of neptunium and plutonium, elements 93 and 94, have been found in uranium ores, it is likely that they are the products of nuclear bombardment by radiation from uranium atoms. 

S. Goriely, L. Siess, in From Lithium to Uranium Elemental tracers of early cosmic evolution ed. by V. Hill et al., Proc. of IAU symposium Nr 228, (Cambridge Cambridge University Press), p. 451 (2005)... 

C5. Cefola, M., The ide of micro- and ultramicrochemistiy in the isolation of the first trans-uranium element Plutonium. Microchem. J. 2, 205-217 (1958). 

The terrestrial occurrence of Ac, Pa, U, and Th is due to the half-lives of the isotopes 235U, 238U and 232Th which are sufficiently long to have enabled the species to persist since genesis. They are the sources of actinium and protactinium formed in the decay series and found in uranium and thorium ores. The half-lives of the most stable isotopes of the trans-uranium elements are such that any primordial amounts of these elements appear to have disappeared long ago. However, neptunium and plutonium have been isolated in traces from uranium13 minerals in which they are formed continuously by neutron reactions such as... 

This chapter discusses production of radionuclides for beneficial use in science, medicine and technology. The nuclear fundamentals for the production processes have been given in Chapters 11 to 14. The formation of radionuclides is discussed in several Chapters e.g. cosmogenic reactions leading to the formation of short-lived radionuclides in nature (Ch. S and 10) thermonuclear reactions leading to the formation of long-lived radioactivity in the universe (Ch. 17) the synthesis of trans-uranium elements (Ch. 16 and 19-21). The production and isolation of separated fission products is treated separately (Ch. 19-21). This chapter discusses aspects of fundamental importance to the production of radionuclides by a variety of methods. Initially the principles are reviewed and, subsequently, the most advanced techniques for investigating short-lived radionuclides are described. 

Plutonium is considered a transuranium (having an atomic number greater than that of uranium) element. It has a very long radiological half-life (86 and 24,000 years for plutonium-238 and -239, respectively), and, therefore, the radioactivity diminishes very slowly. Spent nuclear fuel is not reprocessed in the United States at the present time, and the fuel must be disposed of intact (Lamarsh 1983). The usual method of disposal has been to place the fuel in suitable containers and bury them in a waste repository. Prior to 1970 solid wastes containing radioactive wastes generated by nuclear power plants were buried at commercial waste sites located at Sheffield, Illinois Beatty, Nevada Morehead, Kentucky Richland, Washington and West Valley, New York. As of 1974 approximately 80 kg of plutonium was contained in this waste (Daly and Kluk 1975). 

Many physicists declared, however, that it would be difficult, if not impossible, to separate Isotope 235 from the more abundant Isotope 238. The Isotope 235 is only 1 per cent of the uranium element. 

Prior to 1940 the periodic table ended at uranium, element number 92. Since that time, no scientist has had a greater effect on the periodic table than Glenn Seaborg FIGURE 2.17). In 1940 Seaboig, Edwin McMillan, and coworkers at the University of California, Berkeley, succeeded in isolating plutonium (Pu) as a product of the reaction between uranium and neutrons. We will talk about reactions of this type, called nuclear reactions, in Chapter 21. 

Nuclear synthesis became feasible after invention of the cyclotron and the discoveries of neutrons and artificial radioactivity. In early thirties a few artificial radioisotopes of known elements were synthesized. Syntheses of heavier-than-uranium elements were even reported. But physicists just did not dare to take the challenge of the empty boxes at the very heart of the periodic system. It was explained by a variety of reasons but the major one was enormous technical complexity of nuclear synthesis. A chance helped. At the end of 1936 the young Italian physicist E. Segre went for a post-graduate work at Berkley (USA) where one of the first cyclotrons in the world was successfully put into operation. A small component was instrumental in cyclotron operation. It directed a beam of charged accelerated particles to a target. Absorption of a part of the beam led to intense heating of the component so that it had to be made from a refractory material, for instance, molybdenum. 

Uranium, element 92, is a member of the actinide family of the periodic table, which includes elements 89-104. It has 3 primordial and 12 artificial or man-made isotopes, all of which are radioactive. The naturally occurring uranium series is headed by which subsequently decays... 

The most recent spate of elemental discoveries is ako based on technological developments, involving the production and harnessing of beams of pure atoms or pure elementary particles such as neutrons. These particles can be fired at each other with great precision to achieve nuclear fusion reactions and to thereby create new elements with extremely high atomic numbers. The initiator of this field was the American chemist Glenn Seaborg, who first synthesized plutonium in 1943 and went on to head research teams that were responsible for the synthesk of many more trans-uranium elements. 

The naming of the later trans-uranium elements is a separate story in itself, complete with nationahstic controversies and, in some cases, acrimonious disputes... 

Another curious case concerns the German chemist Otto Hahn, whose name was unofficially given to the element hahnium only to be removed later and changed to the name dubnium after the place where several trans-uranium elements were synthesized. Meanwhile, an element has been named after Hahn s onetime colleague Lise Meitner. To many observers, this is a just move since Hahn had been awarded the Nobel Prize for the discovery of nuclear fission while Meitner, who had participated in many of the crucial steps in the work, was denied the prize. To others, it represents an excess of political correctness. 

Normally, 30% to 4S% of the 85 fuel elements in the reactor will be 1.8 w/o plutonium in aluminum, the remainder swaged natural uranium oxide. Three loadings were given particular attention in the critical tests. A two-zone loading contained 36 plutonium elements in the periphery and 49 uranium elements in the center. A three-zone loading contained 30 plutonium elements in a ring... 

The material balance in the NFC for a generic case can be sununarized, as detailed later, based on seminar material from the European Nuclear Euel Management. Starting with 20,000 tons of ore that contains 1% uranium that after milling is reduced to 230 tons of uranium ore conceutrates (of which 195 tons consist of uranium). This is converted to 288 tons of UF and after enrichment one part is enriched to 4% 2 U (35 tons UFg containing 24 tons uranium) and the rest (254 tons UFg containing 171 tons uranium) is in the tails. The enriched uranium is converted into 27 tons of UO2 from which electricity (7000 million kWh) can be produced in the reactor. The spent fuel will contain 23 tons of uranium (-0.8% U), -240 kg of plutonium, -720 kg of fission products, and some trans-uranium elements. 

---