Separative work unit

The second term in brackets in equation 36 is the separative work produced per unit time, called the separative capacity of the cascade. It is a function only of the rates and concentrations of the separation task being performed, and its value can be calculated quite easily from a value balance about the cascade. The separative capacity, sometimes called the separative power, is a defined mathematical quantity. Its usefulness arises from the fact that it is directly proportional to the total flow in the cascade and, therefore, directly proportional to the amount of equipment required for the cascade, the power requirement of the cascade, and the cost of the cascade. The separative capacity can be calculated using either molar flows and mol fractions or mass flows and weight fractions. The common unit for measuring separative work is the separative work unit (SWU) which is obtained when the flows are measured in kilograms of uranium and the concentrations in weight fractions. 

In 1985, owiag to the declining demand by the nuclear power industry for enriched uranium, the Oak Ridge gaseous diffusion plant was taken out of operation and, subsequently, was shut down. The U.S. gaseous diffusion plants at Portsmouth, Ohio and Paducah, Kentucky remain ia operation and have a separative capacity of 19.6 million SWU (separative work unit) per year which as of this writing is not fully utilized. 

The capacity of processes employing diffusion and mass separation is reported on the basis of the work required, and is expressed as separation work units. (The SWU is a measure of the work required to... 

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). 

Price of natural uranium ore concentrates, 31.SSAb UaOg Price of natural UFj, 89.11/kg U Cost of separative work, 100/separative work unit content of enrichment plant tails, 0.3 w/o... 

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... 

The third column gives the number of separative work units required to produce 1 kg of product, S/Ep, from Eq. (12.155). The units of S are kilograms of uranium, but are conventionally referred to as SWUs (for separative work units). 

Gaseous diffusion. Table 14.3 lists gaseous diffusion plants in operation in 1977 and those then under construction, planned, or under consideration. Part 1 of Table 14.3 lists plants in operation at that time. The three large plants of the UJS. Department of Energy (DOE) had a capacity of over 17 million kg separative work units (SWU) per year when supplied with the maximum amount of electric power, 6100 MW, they could then utilize. 

Owner Location Capacity, million kg separative work units per year ... 

On this separative capacity basis of 1 kg separative work unit per year, from (14.109), Q kW A kg SWU/yr... 

A gaseous diffusion plant is to be designed for a capacity of 10.8 million kg uranium separative work units per year with the following feed, product, and tails compositions (w/o = weight percent). 

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. 

The term separative work unit (SWU) is used to quantify the output of the enriching plants and to describe the supply and demand for enriching service. It is not a quantity of material. It is the measure of the effort spent to separate a given quantity into two streams, one having a higher concentration of the other lower. 

As most of the excavated uranium is subsequently used as nuclear fuel, the price of conversion of the ore (yellow cake) to UFg, the price of enrichment (separative work units—SWU), the cost of deconversion of the enriched UF to uranium oxide (or other chemical forms), and the production of fuel elements determine economic factors. In addition, the cost of electric power production by nuclear power plants in comparison with other plants (gas, coal, and oil) and the overall cost of disposal of the waste from all these processes will influence the worthiness of uranium extraction. In view of the rapid changes in the prices of these processes, it is difficult to assess the threshold concentration of uranium in the ore that will make mining viable economically. Furthermore, nations or organizations that cannot purchase uranium... 

The capacity of processes employing diffusion and mass separation is reported on the basis of the work required, and is expressed as separation work units. (The SWU is a measure of the work required to separate uranium of a given U-235 content into two components, one having a higher and the other a lower U-235 content.) It takes 5.3 SWU to enrich natural uranium to 3.44 percent U-235. The Department of Energy facility has the capacity of 19 million SWU, and there is a world capacity of 46 million SWU (Table 31.11.)... 

TABLE 31.11 Separation Work Unit Requirements (SWU/kg product) ... 

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