Uranium lifetimes

Such a recycling of TRUs also has a positive impact upon lifetime uranium utilization. In ORNL studies, at the end of the 30-year cycle, there would be 736 kg of Pu of which 331 kg would be fissile 239 Pu and 241 Pu. Along with this would be 136 kg of 237 Np and small amounts of Am and Cm (quantities not reported). There would also be enough uranium left to start the next cycle with clean salt, leaving the TRUs as source of fissile top-up. This should save approximately 5%-10% on the lifetime uranium utilization. Thus, the DMSR without any recycling requires about 1525 tonnes uranium lifetime, with U only recycling requires 850 tonnes, and with U -i- TRU recycling requirements are down to perhaps 800 tonnes. 

Mays, C.W., Rowland, R.E., and Stehney, A.F. (1985). Cancer risk from the lifetime intake of radium and uranium isotopes, Health Phys. 48,635. 

To achieve a fuel management scheme with the lowest fuel cycle cost consistent with the current thermal and material performance limits, the following parameters are selected (l)a fuel cycle incorporating uranium/thorium (2) a fuel lifetime of four years (3) an average power density of 8.4 W/cm3 and (4) a refueling frequency of once a year. 

Edmond Becquerel (1820-1891) was the nineteenth-century scientist who studied the phosphorescence phenomenon most intensely. Continuing Stokes s research, he determined the excitation and emission spectra of diverse phosphors, determined the influence of temperature and other parameters, and measured the time between excitation and emission of phosphorescence and the duration time of this same phenomenon. For this purpose he constructed in 1858 the first phosphoroscope, with which he was capable of measuring lifetimes as short as 10-4 s. It was known that lifetimes considerably varied from one compound to the other, and he demonstrated in this sense that the phosphorescence of Iceland spar stayed visible for some seconds after irradiation, while that of the potassium platinum cyanide ended after 3.10 4 s. In 1861 Becquerel established an exponential law for the decay of phosphorescence, and postulated two different types of decay kinetics, i.e., exponential and hyperbolic, attributing them to monomolecular or bimolecular decay mechanisms. Becquerel criticized the use of the term fluorescence, a term introduced by Stokes, instead of employing the term phosphorescence, already assigned for this use [17, 19, 20], His son, Henri Becquerel (1852-1908), is assigned a special position in history because of his accidental discovery of radioactivity in 1896, when studying the luminescence of some uranium salts [17]. 

The vast majority of the studies reported have concerned the metals thorium and uranium, particularly the latter, due to accessibility of raw materials, ease of handling, and the long lifetimes of the relatively weakly a-emitting elements Th and U. In many cases, compounds of neptunium and plutonium with similar formulae to U and Th analogues have been made and found to be isomorphous and thus presumably isostructural. This chapter will therefore commence with, and concentrate largely on, the chemistry of complexes of these elements, followed by sections on the other actinides. 

The report estimated a lifetime risk of excess bone sarcomas per million people of 1.5 if soluble uranium isotopes were ingested at a constant daily rate of 1 pCi/day (0.037 Bq/day). The number of bone sarcomas that occur naturally in a population of a million people is 750. However, no quantitative risk coefficient estimates for developing human exposure protection benchmarks were provided in this report. In addition, the BEIR IV analysis was presumably based on generic short-lived alpha-emitting sources, such as radon that have a higher potential for inducing cancer, and not on radionuclides with relatively longer radioactive half-lives like and Perhaps more importantly, the BEIR IV report... 

Analysis of the natural reactors at Oklo gives valuable information about the migration behaviour of fission products and actinides in the geosphere. Uranium and the lanthanides have been redistributed locally. Plutonium produced in the Oklo reactors did not move during its lifetime from the site of its formation 85-100% of the lanthanides, 75-90% of the Ru and 60-85% of the Tc were retained within the reactor zones. Small amounts of U, lanthanides, Ru and Tc moved with the water over distances of up to 20-50 m. 

The heaviest element that has been investigated by K-edge EXAFS is iodine (Z = 53), which has its K-edge at 0.37 A (33,500 eV) and has a lifetime broadening of >7 eV. For the higher Z elements, L-edge XAS can be recorded, concomitant with the excitation of a 2s or 2p electron typically, L-edge data can be recorded for molybdenum (Z = 42) to uranium (Z = 92). 

Astatine is a radioactive element that occurs in uranium ores, but only to a tiny extent. Its most stable isotope, °At, has a half-life of 8.3 h. The isotopes formed in uranium ores have much shorter lifetimes. The properties of astatine are surmised from spectroscopic measurements. Astatine is created by bombarding bismuth with alpha particles in a cyclotron, which accelerates particles to high speed. 

Nuclear fission energy of the type currently in use has the potential to provide enough energy for the operation of civilization, but it presents much the same supply lifetime problem as fossil fuels. The waste products present a severe environmental problem. The problem is very different from that presented by fossil fuels but possibly more dangerous. Despite much criticism of the use of fission nuclear power, its use may be preferred to fossil fuels because of the lack of other peaceful use for uranium and the fact that the waste products can be confined. Remember, fossil fuels wastes are not confined. They are dispersed through the ecosphere as acid rain and carbon dioxide. 

If the operational conditions and design of a reactor are adjusted to maximize the amount of Pu produced it is possible to operate the reactor to produce more fertile isotopes than were originally used to start the reactor. This operational mode is called the breeder reactor. The breeder reactor can greatly extend the amount of potential energy available from uranium because it is possible to use the 99.3% U present in natural uranium, as fuel. It is also possible to use thorium (Th" ) in a breeder reactor to produce fertile U. The use of the breeder reactor will extend the lifetime of the nuclear fission energy source to several hundred years. 

During its lifetime, a fusion reactor presents little radiation hazard. The internal structure, particularly the vacuum containment vessel and the heat exchanger, will be subject to intense neutron bombardment. The neutrons will convert some of the elements of the structure into long-lived radioactive isotopes. Selecting construction materials that do not easily become activated can minimize radioisotope production. No material is entirely resistant to neutron activation, thus the decommissioning of a fusion reactor will require the handling and disposal of potentially hazardous radioactive isotopes. Because of the lack of uranium, plutonium, and fission products, the total radiation exposure hazard from the decommissioned fusion reactor is 10,000 to 1,000,000 less than from a decommissioned fission reactor. 

Janes, G. S. Itzkan, I. Pike, C. T. Levy, R. H. and Levin, L.,"Two-Photon Laser Isotope Separation of Atomic Uranium Spectroscopic Studies, Excited-State Lifetimes, and Photoionization Cross Sections," IEEE, J. Quantum Electron, 1976, QE-12, 111-120. 

Since the lifetimes of the uranium isotopes and are difrerent, the isotopic ratio between their end products Pb and Pb can also be used for age determination. One can derive the relationship... 

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