Isotope separation Separative work units

The gas centrifuge process uses long multipy overcritically rotating cylinders, in which the heavy uranium isotope is enriched at the cylinder wall and the lighter isotope is enriched at the center of the centrifuge. Enrichment to 3 to 5% is achieved in less than ten stages connected in series. The energy consumption is ca. 50 kWh/kg SWU (SWU = separation work units). 

In many isotope separation plants the initial cost of the plant is proportional to the separative capacity of the plant and the annual operating costs are proportional to the amount of separative work done per year. In such cases the annual charges for plant investment plus aimual operating costs exclusive of feed, in dollars per year, equal Dcs, where Z) is the annual separative capacity in kilograms of uranium per year and cs is the unit cost of separative work, in dollars per kilogram of uranium of separative work units ( /kg SWU). If kg of feed is charged per year at a unit cost of cp /kg, the total annual cost c is... 

Eq. 9 Is of major Importance for estimating the size and cost of an Isotope separation plant. It Indicates that the total flow Is a product of two factors the first of these, proportional to l/(a-l) Is a function only of the elementary separation factor which Is determined by the separation process used. The second factor [In square brackets], which Is usually called the separative duty or separative work units (S.W.U.) Is a function only of quantities and concentrations of feed, product, emd waste. It has the same dimensions as those used for the quantities of material, and Its value Is Independent of the process used to accomplish the separation task. The significance of the magnitude of the elementary factor Is Immediately apparent a two-fold reduction In (a-1) requires an Increase In the total flow by a factor of 4. Since for a gaseous diffusion process, the total flow rate Is closely related to the total area of porous barriers, the total pumping capacity and the total power consumption required, all the associated costs vary proportionately. 

It is interesting to compare the economics of gas centrifugation to gaseous diffusion, albeit crudely. London (1961) divides enrichment cost into two principal categories (1) specific investment, i.e., capital cost per separative work unit (SWU) amortized over the plant life, and (2) power cost per SWU. (SWU, which is a function of quantities and concentrations of feed, product, and waste provides a quantitative measure of the isotope separation task for any conceivable process.) The latter comprises the bulk of operating costs. The estimates, which are crude, clearly demonstrate an advantage for gas centrifugation. 

British Columbia, and three at the U.S. Army Ordinance Works operated by the DuPont Company at Morgantown, West Virginia Cluldersburg, Alabama and Dana, Indiana. The plant at Trail used chemical exchange between hydrogen gas and steam for the initial isotope separation followed by electrolysis for final concentration. The three plants in the United States used vacuum distillation of water for the initial separation followed by electrolysis. Details of these plants and their operations may be found in the Hterature (10). 

Most often W, P and F are chosen to have units of mass (x , as always, is isotope fraction), in which case separative work has the dimension of mass and can be thought of as the mass flow rate multiplied by the time required to yield a given quantity of product. The cost of isotope separation is then obtained by assigning a cost to one separative work mass unit (kgSW or SWU). 

The alkoxides of actinides are rarely studied except the derivatives of uranium and thorium, as interest in the alkoxides of these 2 elements has increased by the hope to use them in the isotope-separation processes. The study of uranium alkoxides was initiated by groups led by Gilman and Bradley in the 1950s. The major part of this work is still carried out at the Nuclear Research Center at Los Alamos in the United States by the group of Sattelberger et al. [1671]. The detailed data on alkoxides ofuranium is provided in a number of... 

Equation (14.111) for the minimum power of 0.0923 kW to produce 1 kg of separative work per year in uranium isotope separation was derived for cross flow on the low-pressure side of the barrier, with the composition of gas on that side y equal to the composition of the net flow u. The purpose of this section is to show that the minimum power requirement could be reduced further by having v greater than y by an appropriate amount and to derive an expression for the optimum difference between v and y and the corresponding power consumption per unit separative capacity. For this minimum wer case, pressures on the high-pressure and low-pressure sides of the barrier must be so low the only flow through the barrier is of the separating, molecular type, and the mixing efficiency on each side of the barrier is unity. 

In Section 2.2.3, the separative power SU was introduced for a single-entry separator in an isotope separation plant via equation (2.2.32a). Expression (2.2.42) was developed for the value function in the case of close separation. The developments in Chapter 2 were carried out in mole fraction units and molar flow rates. In the market for nuclear fuels, an estimate of the energy requirement for isotope separation is sometimes expressed in units of separative work, SWU, which is essentially identical to the SU expression (2.2.32a) containing expression (2.2.42) for the value function, except mass units are used for the flow rates Wa, Wa, Wt/. 

From Figs. 1.1 and 1.2 it follows that the main end products of the uranium and thorium series are isotopes of lead (at the time referred to as Pb206.5 and ThO2208.4). The end products are thus isotopes of lead differing by two mass units. This observation became the motivation for the measurement of atomic weights of lead samples separated from thorium and uranium minerals. In his Nobel Lecture, Soddy describes this work as follows ... 

Working on a planet in another galaxy, where laboratory temperatures are 200 K, a scientist discovers a new force field selective for isotopes whose separation promises to fuel a bomb to blow an adjacent planet to smithereens. The maximum force exerted by this field on the two isotopes is 5.00 x 1010 dyn/mol. What is the lowest plate height the scientist can hope to achieve in an Sc-class separation In this field the velocity difference is 2% of the mean (which is remarkably selective for isotopes). What length separation tube is needed to separate the isotopes at unit resolution (Remember, lofty goals are worth the trouble.)... 

With a technique known as electromagnetic separation, applications of mass spectrometry began to spread away from the previous academic work into more practical fields like nuclear isotope enrichment. Mass spectrometers have been engaged on a preparative scale (calutrons), notably in the United States where in 1943 several kg of destined for the manufacture of the first atomic bombs were isolated (the Manhattan Project). This, now dated, procedure, which has a low flow rate of under 10 Pa, is still occasionally in use by other countries. 

Laboratories that are used for radioisotope work in the United Kingdom must either be registered as Supervised or Controlled areas. Both imply restricted access, separate storage facilities for radioisotopes, and careful management of the use to which the laboratory is put. To maintain a separate laboratory away from the main working laboratory is usually an expensive option as it implies extra rent payable on the occupied space, and usually the duplication of equipment already present in a main laboratory. Registration to hold and dispose of isotopes requires both an initial payment to Her Majesty s Inspectorate of Pollution, plus a yearly retainer. 

At the Nuclear Research Centre at Karlsruhe (FRG) oxygen-17 and -18 are separated by distillation of heavy water. This work, which is carried out in collaboration with Norsk—Hydro, capitalises on the fact that there is enrichment of the heavy oxygen isotopes in the Norwegian manufacture of heavy water [23]. In this plant, the features of which have been described [56], oxygen-18 is produced at 99.9 atom%. Intermediate product is converted into H2O and fed to a distillation unit in order to produce useful enrichments of oxygen-17 (approaching 30 atom%). Water- 0 (depleted in both and 0) is produced at 99.99 atom% 0 [56]. 

Quantitatively, the dependence of the efficiency of a separating unit on the combined effects of throughput and enrichment is characterized by the separative power of the unit. To describe this feature of the separating unit, the work the device does on the fluid it processes is viewed as increasing the value of the material. The value of a unit amount of material of isotopic composition x is denoted by V(x), which is termed the value function (invented by Peierls and Dirac). The separative power of the unit is defined as the increase in the value of the streams leaving the unit over the feed stream. A value balance can be made in a manner analogous to a material balance. For the separating unit shown in Fig. 3, this balance yields... 

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