Uranium ratios

O Hara MJ (1968) The bearing of phase equilibria studies in synthetic and natural systems on the origin and evolution of basic and ultrabasic rocks. Earth Sci Rev 4 69-133 O Nions RK, McKenzie D (1993) Estimates of mantle thorium/uranium ratios from Th, U and Pb isotope abundances in basaltic melts. Phil Trans Royal Soc 342 65-77 Oversby V, Gast PW (1968) Lead isotope compositions and uranium decay series disequilibrium in reeent volcanic rocks. Earth Planet Sci Lett 5 199-206... 

Allegre CJ, Dupre B, Lewin E (1986) Thorium/uranium ratio of the Earth. Chem Geol 56 217-227 Allegre CJ, Turcotte D (1986) Implications of a two-component marble-cake mantle. Nature 323 123-127 Asimow PD, Hirschmann MM, Ghiorso MS, O Hara MJ Stolper EM (1995) The effect of pressure-induced solid-solid phase transitions on decompression melting of the mantle. Geochim Cosmochim Acta 59 4489-4506... 

Allegre CJ, Dupre B, Lewin E (1986) Thorium/uranium ratio of the Earth. Chem Geol 56 219-227... 

Russell AD, Emerson S, Mix AC, Peterson LC (1996) The use of foraminiferal U/Ca as an indicator of changes in seawater uranium content. Paleoceanography 11 649-663 Rutherford E, Soddy F (1902) The cause and nature of radioactivity Part 11. Phil Mag Ser 6 4 569-585 Sacked WM (1960) Protactnium-231 content of ocean water and sediments. Science 132 1761-1762 Sacked WM (1958) Ionium-uranium ratios in marine deposited calcium carbonates and related materials. 

Salaymeh S, Kuroda PK. 1987. Variation of the thorium to uranium ratio in rain Thorium-230 chronology of the eruptions of Mt. St. Helens and El Chichon volcanoes. J Radioanal NucI Chem 116 261-269. 

A further argument was advanced by Veal et al.. A linear relationship was found to exist between the XPS intensity of the main oxygen valence band and the oxygen-to-uranium ratio of the different uranium oxides investigated (Fig. 23). This was interpreted as indicating that this band consists entirely of 2p states (perhaps 6 d hybridized) with no 5f contribution, as expected in a localized 5f picture. (The 5f contribution, if present, would have caused deviations from this hnear relationship, especially because of the very large photoionization f cross-section.)... 

O Nions, R.K. and McKenzie, D., 1993. Estimates of mantle thorium/uranium ratios from Th, U and Pb isotope abundances in basaltic melts. Phil. Trans. R. Soc. Lond. A., 342 65-77. 

The plutonium-uranium ratio in liquid solution was not consistent with that added. There seems little doubt that this discrepancy resulted from the precipitation of two different compounds as the alloy cooled from higher temperatures. Pu2Zn17 decomposes peritectically at 1083° K. to form PuZn8 and liquid (3). Presumably the PuZn8-based three-component form dissolves and reprecipitates on the U2Zn17 matrix near this temperature, as the temperature is lowered. The selected data of P/540 (5) show slightly different slopes for the plots of log solubility vs. reciprocal temperature for Pu-Zn and U-Zn. This variance probably reflects difference in technique by the two groups of experimenters, since it does not show in parallel Pu-Zn and U-Zn experiments by Elliott and coworkers on which that part of P/540 was based. 

The ratio of plutonium to uranium in the zinc solution remaining after distillation is dependent on how much zinc is distilled away. At the nominal end-point of the distillation the plutonium/ uranium ratio is 1 4. 

The plutonium/uranium ratio may be adjusted to the desired plutonium enrichment by the addition of the appropriate amount of uranium. 

We are limited in this modeling process by the accuracy with which measurements can be made and by the accuracy of the fission yields and neutron reaction cross sections which are used to interpret the results. As an example consider the Nd- Nd fission product pair, which has been used as an indicator of thermal neutron fluence because the capture cross section for the former is large and for the latter is small. The thermal cross section for l53Nd has recently been listed as 325 ( 10) barns (20), and more recently as 266 barns (11). Using the 325-barn value we deduce an age of about 2 to 27T billion years from neodymium to uranium ratios in the Oklo reactors, while an age of about 1.8 billion years is obtained using the 266-barn figure. 

The lead-uranium method for determining geologic age indicates an age of about 1.75 billion years, in substantial agreement with the "Nd/U" age deduced with the 266-barn cross section ( ). The observed neodymium to uranium ratios can also be reconciled with an age of 1.8 billion years and a 325-barn cross section by adopting the unlikely proposition that a uniform twenty percent of the uranium has dissolved and been transported away from the reactor since it shut down (19). 

One of the more interesting questions about the Oklo reactors is how long they remained critical. The answer is intimately related to the fraction of fissions in 238U, for reasons discussed below, which is in turn related to the concentrations of uranium in the ore and to the amount of water present. If we assume that 1/2 of the radiogenic lead is now missing then a present day uranium concentration of 58% extrapolates to a 70% concentration 1.8 billion years ago. At such a concentration the optimum hydrogen to uranium ratio for criticality is in the range of two to ten as is shown in Fig. 2, while at lower concentration the optimum moves up to values of 5 to 20. Since it seems likely... 

Another more sensitive way to detect a natural reactor is to look for fission products such as ruthenium, palladium, or tellurium which are rare elements in the earth s crust. As a result of preliminary experiments conducted at the Idaho National Engineering Laboratory ruthenium from spontaneous fission of 238U has been detected in a natural uranium ore, thus illustrating the sensitivity of the method and also the possibility of using ruthenium to uranium ratios to date uranium ores. The burn-up of... 

To permit control of the plutonium/uranium ratio in recovered fuel... 

In this process, oxide fuel is dissolved in a molten chloride salt mixture through which Q2-HCI gas is flowing. Dissolved uranium and plutonium are then recovered as oxides by cathodic electrodeposition at 500 to 700°C. The process was demonstrated with kilogram quantities of irradiated fuel, with production of dense, crystalline UO2 or UO2-PUO2 reactor-grade material. Difficulties were experienced with process control, off-gas handling, electrolyte regeneration, and control of the plutonium/uranium ratio. Development has been discontinued. 

The rate of dissolution of PUO2 in nitric acid is slower than UO2 and depends on the plutonium/uranium ratio, the methods used to fabricate fuel, and the conditions of irradiation. At one extreme, plutonium produced at low concentration in UO2 by transmutation dissolves almost as rapidly as the associated UO2. At the other extreme, plutonium present as PUO2 mixed mechanically with UO2 without proper sintering dissolves much more slowly and less completely than UO2. Plutonium present as a solid solution (U,Pu)02 at the concentration of 20 to 25 percent used in breeder-reactor fuel dissolves at an intermediate rate. ... 

In the IBX column thorium in solvent HAP leaving the HA column was returned to the aqueous phase by stripping with 0.2 Af HNO3 thorium strippant IBX. This reduced the thorium/uranium ratio in the solvent IBU leaving the column to about 1 5.5. 

Process results. Decontamination factors observed by Kuchler et al. [K7] in processing 54,000 MWd/MT fuel with thorium/uranium ratio of 5.9, cooled 346 days, are listed in Table 10.19. Uranium losses were 0.012 percent to thorium product, 0.004 percent to solvent from 2C, and... 

Hydroxylamine is used for plutonium reduction instead of cathodic reduction as in the Barnwell flow sheet Fig. 10.11, because the plutonium/uranium ratio in this LMFBR fuel is 10 times that in LWR fuel and because electrolytic reduction has not been demonstrated for this high plutonium content. 

Allegre CJ, Dupre B, Lewin E (1986) Thorium/uranium ratio of the Earth Chem Geol 56 219-227 Allegre CJ, Hamelin B, Dupre B (1984) Statistieal analysis of isotopie ratios in MORE the mantle blob cluster model and the convective regime of the mantle. Earth Planet Sei Lett 71 71 -84 Allegre CJ, Hofmaim AW, O Nions RK (1996) The argon eonstraints on mantle stracture. Geophys Res Lett 23 3555-3557... 

Therefore, the problems which faced the would-be designers of chain reactors early in 1941 were (1) the choice of the proper moderator to uranium ratio, and (2) the size and shape of the uranium lumps which would most likely lead to a self-sustaining chain reaction, i.e., give the highest multiplication factor. In order to solve these problems, one had to understand the behavior of the fast, of the resonance, and of the thermal neutrons. We were concerned with the second problem which itself consisted of two parts. The first was the measurement of the characteristics of the resonance lines of isolated uranium atoms, the second, the composite effect of this absorption on the neutron spectrum and total resulting absorption. One can liken the first task to the measurement of atomic constants, such as molecular diameter, the second one, to the task of kinetic gas theory which obtains the viscosity and other properties of the gas from the properties of the molecules. The first task was largely accomplished by Anderson and was fully available to us when we did our work. Anderson s and Fermi s work on the absorption of uranium, and on neutron absorption in general, also acquainted us with a number of technics which will be mentioned in the third and fourth of the reports of this series. Finally, Fermi, Anderson, and Zinn carried out, in collaboration with us in Princeton, one measurement of the resonance absorption. This will be discussed in the third article of this series. 

It can be used as a 0-1M solution in kerosene for the extraction of thorium from the very dilute sulphate liquors remaining after the extraction of uranium by ion-exchange. This applies particularly to the uranium ore from the Blind River area of Canada, where the thorium-to-uranium ratio may be as high as 1 4. A completely sulphate system is employed at pHl to 2 with a half saturated solution of sulphurous acid as an impurity strip. The thorium is backwashed into nitric acid or another nitrate solution. 

The reduced power density of the core ensures low thermal loads under normal and emergency operating conditions. The chosen water/uranium ratio provides for favourable fuel cycle economy. 

The carbon-to-uranium ratio for equal wet and dry bucklings ( cross-over ) decreases with rod size and also with water-to-uranium ratio. The measured crossover lattice spacings for the particular configniations reported here are 8.3 in. for the 1.92-In. elements and 9.5 in. for the 2.5-in. elements. 

Fig. 1. Minimum Core Radius as a Function of Water to Uranium Ratio...

The system considered is composed of two 5-gal cans containing UO2 of various densities, 5 wt% enriched in the U Isotope, and with a hydrogen-to-uranium ratio of 0 45. The cans are contain In a 16-gal drum which is in turn centered and supported within a 55-gal drUpi Iv insulating material in which the hydrogien content was allowed to vary for. calculatlonal inirposes. The zero-current boundary conditions are implied at file surface of the outer drum that is, assuitaing an infinite array of such containers. 

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