Actinides uranium-plutonium

Canberra, (n.d.). Actinide (uranium/plutonium) lung counter model 2270 http //www.canbeira.com/ ptoducts/hp radioprotection/model2270-lung-counter.asp (accessed August 3, 2014). 

Heat capacity data for ions in aqueous solution over the temperature range 25-200°C. Such data for ionic species of uranium, plutonium, other actinides and various fission products such as cesium, strontium, iodine, technetium, and others are of foremost interest. 

The remaining exceptions concern the lanthanide series, where samarium at room temperature has a particular hexagonal structure and especially the lower actinides uranium, neptunium, and plutonium. Here the departure from simple symmetry is particularly pronounced. Comparing these three elements with other metals having partly filled inner shells (transition elements and lanthanides), U, Pu, Np have the lowest symmetry at room temperature, normal pressure. This particular crystallographic character is the reason why Pearson did not succeed to fit the alpha forms of U, Pu, and Np, as well as gamma-Pu into his comprehensive classification of metallic structures and treated them as idiosyncratic structures . Recent theoretical considerations reveal that the appearance of low symmetries in the actinide series is intimately linked to the behaviour of the 5f electrons. 

Different nuclear models and contributions of the Breit interaction between valence, inner and outer core shells of uranium, plutonium and superheavy elements El 12, E113, and El 14 are considered in the framework of allelectron four-component and (G)RECP methods. It is concluded on the basis of the performed calculations and theoretical analysis that the Breit contributions with inner core shells must be taken into account in calculations of actinide and SHE compounds with chemical accuracy whereas those between valence and outer core shells can be omitted. 

The seventh-period inner transition metals are called the actinides because they fall after actinium, Ac. They, too, all have similar properties and hence are not easily purified. The nuclear power industry faces this obstacle because it requires purified samples of two of the most publicized actinides uranium, U, and plutonium, Pu. Actinides heavier than uranium are not found in nature but are synthesized in the laboratory. 

After a few years of storage, the main radioactive heat emitters in HLW are 90Sr and 137Cs. In addition, extremely long-lived actinides—neptunium, plutonium, americium, and curium—should be collected for transmutation in the future. Therefore, different flowsheets can be proposed for waste processing. It is possible to extract each radionuclide in the special extraction (sorption) cycle, for example, uranium and plutonium in the PUREX process, and after that, minor actinides (MAs) by the TRUEX process,4 strontium by the SREX process,5,6 and cesium by sorption7 or extraction.8... 

A mixture of well-known extractants, di-(2-ethylhexyl)phosphoric acid (HDEHP) and CMPO, in n-paraffin was used for the study of combined extraction of different actinides (americium, plutonium, and uranium) and lanthanides (cerium and europium) and their separation from fission products (cesium, strontium, ruthenium, and zirconium).54 Combined extraction of MAs and lanthanides was studied together with group separation of MAs from lanthanides by selective stripping with a solution of diethylenetriaminepentaacetic acid (DTPA), formic acid, and hydrazine hydrate. This solution strips only MAs, leaving lanthanides in the organic phase. Subsequently, the lanthanides are stripped using a mixture of DTPA and sodium carbonate. 

The effect of radiation on actinide containing materials and solutions can be altered by careful selection of the isotopes. For uranium, plutonium, americium, and curium, there are a number of different isotopes with varying half-lifes that can be used. In Table 2, the commonly available isotopes of the... 

Actinide nitrides are known for Th through Cm. All of the nitrides are high melting compounds with melting points of 2630 °C, 2560 °C, and 2580 °C for Th, Np, and Pu, respectively. The actinide nitrides can decompose to give N2. Thorium, uranimn, and plutonium nitrides are well known and can be used as nuclear fiiels. Fuels of this type, especially uranium and mixed uranium plutonium nitrides, can be used in lead-cooled fast reactors, which have been proposed as a possible next-generation nuclear reactor and for use in deep-sea research vehicles. 

After bum-up, the fuel elements are stored under water for radiation protection and cooling, for at least several months and generally for about one year. Afterwards, they may be either disposed of or reprocessed in order to separate the fuel into three fractions uranium, plutonium, and fission products including the rest of the actinides. Uranium and plutonium may be re-used as nuclear fuel, thus closing the U/Pu fuel cycle. The fission products and the rest of the actinides are converted into chemical forms that are suitable for long-temi storage. 

In the case of the U-Pu fuel cycle, the main steps of reprocessing are separation of uranium, plutonium and fission products including the other actinides. U and Pu are to be recovered in high purity and free from fission products and other actinides, in order to make further use possible. Pu causes problems, because it may be used... 

The pentavalent oxidation state is accessible for the early actinides uranium, protactinium, neptunium, and plutonium. Pentavalent species with neutral Group 16 bases can include either adducts of AnXg or complexes incorporating oxo-containing cations, AnO " or An02". ... 

Some of the pyrochemical processes have more potential for being proliferation resistant because of the great similarity of the chemistry of uranium, plutonium, and some of the fission products in the chosen systems. Ordinary processes are designed to maximize differences in chemical behavior in order to separate constitutents. For some of the pyrochemical processes the chemical equilibria are such that partial separations are possible but complete separations are thermodynamically limited. For example, excess uranium can be separated from plutonium by precipitation in a molten metal such as zinc only until both are present in about equal quantities in solution, but no further ( 3, 4). Likewise, the solubility of fission products is selectively limited. Only a portion of elements such as ruthenium will stay in solution and be removed 05). The majority of the ruthenium precipitates with the actinides. A complete separation is again thermodynamically limited. As a result only a modest dependence needs to be placed on process equipment and facility design for proliferation resistance. 

Salt Transport Processing (8, 9, 10, 11) The selective transfer of spent fuel constitutents between liquid metals and/or molten salts is being studied for both thorium-uranium and uranium-plutonium oxide and metal fuels. The chemical basis for the separation is the selective partitioning of actinide and fission-product elements between molten salt and liquid alloy phases as determined by the values of the standard free energy of formation of the chlorides of actinide elements and the fission products. Elements to be partitioned are dissolved in one alloy (the donor... 

The extended radiation time for the domestic fuel increases the quantity of fission products and the higher actinides. Pure plutonium product poses nuclear weapons proliferation risk and is the primary reason reprocessing is not practiced in the United States. The modified PUREX process has been practiced on an industrial scale in Europe and supports the production of mixed uranium-plutonium fuel. Blended UO2 and PUO2 powder is compacted and sinter to form the mixed oxide (MOX) fuel pellets much like the enriched UO2 fuel. Natural and depleted uranium can be used to prepare MOX fuel and is the demonstrated option to recover fuel values from spent fuel. 

Sb, 235.137cs. 205p, gjjj various actinides (uranium, neptunium, americium, and plutonium). They originate not only from the nuclear industry, but also from other industries and from medicine and research (Amiro, 1993 Ouzounian, 1996). 

The RWMC assigned a high priority to the critical review of relevant chemical thermodynamic data of inorganic species and compounds of the actinides uranium, neptunium, plutonium and americium, as well as the fission product technetium. The first four books in this series on the chemical thermodynamics of uranium, americium, neptunium and plutonium, and technetium originated from this initiative. 

To designate isotopes of uranium, plutonium, and other actinide elements, it has become conventional to use two-digit subscripts, such as 49 for Pu, in which the first digit is the atomic number minus 90 and the second digit is the last digit of the mass number. 

Although TBP is a relatively stable organic compound, it does undergo slow hydrolysis to form di-n-butyl phosphate (DBP). Although the presence of DBP increases the distribution coefficients of uranium, plutonium, and other actinides, it interferes with the separation of plutonium from uranium, and it makes complete stripping of these elements difficult. DBP forms an insoluble compound with thorium. DBP formation is appreciable only when the... 

Actinide Radioactivity in Uranium and Uranium-Plutonium Fuel... 

There are many examples of the studies on SLM for nuclear applications in the literature. SLMs were tested for high-level radioactive waste treatment combined with removal of actinides and other fission products from the effluents from nuclear fuel reprocessing plants. The recovery of the species, such as uranium, plutonium, thorium, americium, cerium, europium, strontium, and cesium, was investigated in vari-ons extracting-stripping systems. Selective permeation... 

Problems relevant in the long-term are the radiotoxicity of the fuel and the long-term risk related to a final repository, which can be steered by an adequate choice of fuel cycle and reactor type. Moreover, it is possible to transmute very long-lived actinides and fission products into less toxic or stable nuclei by means of specific nuclear reactions. Following figure summarises these options for the back-end in the case of the uranium-plutonium fuel cycle. 

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