The Nuclear Fuel Cycle

Predictions of future 1 releases to the environment obviously depend on assumptions of future growth of the nuclear energy industry. Spch projections are difficult to make and, in the past, have proven to be unreliable, since they reflect uncertainties in projecting population grpyrth and energy demand, and the indeterminate partition of energy 

Recently, each years published projections of nuclear power growth have indicated a lower expectation of installed generating capacity (Laue, 1982). A 1982 projection for the United States (U.S. Department of Energy, 1982) reports that spent fuel discharged from U.S. power reactors as of December 1981 totalled 8100 metric tons of uranium equivalent (MTU), only 230 MTU of which had been reprocessed. The installed nuclear power capacity was predicted to increase gradually from 61 GWe in 1982 to 170 GWe by the year 2000. Because of uncertainties in these estimates, it is considered unwise to project the world-wide inventories of beyond 2000. There is sufficient tittie before the year 2000 to develop reasonable estimates of environmental impacts of plants now built or to be constructed by the end of the century. 

An estimated 4 Ci of cbuld have been in the 230 MTU of spent fuel processed at the Nuclear Fuel Services plant at West Valley, NY, depending upon the reactor exposure of the fuels. Most of this probably was sent to the high level waste storage tanks on site. 

About 170 Ci of were contained in the 7870 MTU of unreprocessed fuel as of December 1981 (U. S. Department of Energy, 1982). 

The projections made by the U.S. Department of Energy (1982) of installed nuclear capacity and the associated masses of spent fuel discharged are reproduced in Table 3.2. The activity of present in the discharged fuel is also given in the table. The latter was calculated 

---

Fig. 6. The nuclear fuel cycle. HLW = high level waste.

The safety principles and criteria used ia the design and constmction of the faciUties which implement the nuclear fuel cycle are analogous to those which govern the nuclear power plant. The principles of multiple barriers and defense-ia-depth are appHed with rigorous self-checking and regulatory overview (17,34). However, the operational and regulatory experience is more limited. 

The sum total of risks of the nuclear fuel cycle, most of which are associated with conventional industrial safety, are greater than those associated with nuclear power plant operation (30,35—39). However, only 1% of the radiological risk is associated with the nuclear fuel cycle so that nuclear power plant operations are the dominant risk (40). Pubhc perception, however, is that the disposition of nuclear waste poses the dominant risk. 

The main technological uses for UO2 are found in the nuclear fuel cycle as the principal component for light and heavy water reactor fuels. Uranium dioxide is also a starting material for the synthesis of UF [10049-14-6] 6 (both critical for the production of pure uranium metal and... 

Nitrides. Uranium nitrides are weU known and are used in the nuclear fuel cycle. There are three nitrides of exact stoichiometry, uranium nitride [2565843-9], UN U2N3 [12033-85-1/ and U4N2 [12266-20-5]. In addition to these, nonstoichiometric complexes, U2N3, where the N/U ratio ranges... 

Fluorides. Uranium fluorides play an important role in the nuclear fuel cycle as well as in the production of uranium metal. The dark purple UF [13775-06-9] has been prepared by two different methods neither of which neither have been improved. The first involves a direct reaction of UF [10049-14-6] and uranium metal under elevated temperatures, while the second consists of the reduction of UF [10049-14-6] by UH [13598-56-6]. The local coordination environment of uranium in the trifluoride is pentacapped trigonal prismatic with an 11-coordinate uranium atom. The trifluoride is... 

In addition to these are studies prepared before President Carter stopped the GESMO (Generic Environmental Statement for Mixed Oxide) that addressed the chemical processing of fissionable material for the nuclear fuel cycle. Some references are Cohen (1975), Schneider (1982), Erdmann (1979), Fuliwood (1980), and Fullwood (1983). 

The Safety of the Nuclear Fuel Cycle, Organization for Eeonomic Cooperation and Development, 1993, p. 206. 

The second part deals with applications of solvent extraction in industry, and begins with a general chapter (Chapter 7) that involves both equipment, flowsheet development, economic factors, and environmental aspects. Chapter 8 is concerned with fundamental engineering concepts for multistage extraction. Chapter 9 describes contactor design. It is followed by the industrial extraction of organic and biochemical compounds for purification and pharmaceutical uses (Chapter 10), recovery of metals for industrial production (Chapter 11), applications in the nuclear fuel cycle (Chapter 12), and recycling or waste treatment (Chapter 14). Analytical applications are briefly summarized in Chapter 13. The last chapters, Chapters 15 and 16, describe some newer developments in which the principle of solvent extraction has or may come into use, and theoretical developments. 

Fuel. The nuclear fuel cycle starts with mining of the uranium ore, chemical leaching to extract the uranium, and solvent extraction with tributyl phosphate to produce eventually pure uranium oxide. If enriched uranium is required, the uranium is converted to the gaseous uranitim hexafluoride for enrichment by gaseous diffusion or gas centrifuge techniques, after which it is reconverted to uranium oxide. Since the CANDU system uses natural uranium, I will say no more about uranium enrichment although, as I m sure you appreciate, it is a major chemical industry in its own right. 

Fig. 3. Schematic illustration of the interface of the nuclear fuel cycle with geochemical/hydrological cycles. The geological repository is the interface for these two cycles. The principal sources of radioactivity (over the long term) are indicated by the radionuclides listed at the centre of each cycle. Total background exposures to radiation are less than 300 mrem/y. The total radiation exposure that can be attributed to the nuclear fuel cycle is less than 3 mrem/y.

Just as important as evaluating the performance of the nuclear fuel cycle, one must also consider the size of the fluxes and reservoirs of the carbon cycle. Present CO2 emissions from fossil fuels and the production of cement are estimated to be 6.3 + 0.4 GtC/y emissions related to changes in land use (e.g., deforestation) are 1.6 0.8 GtC/y (Schimel et al. 2001). At present, the reduction of C02 emissions that can be attributed to the use of nuclear power is 0.5 GtC/y. Thus, the uncertainties in the major fluxes in the carbon cycle are approximately the same as the present impact of nuclear power on C02 emissions (Sarmiento Gruber 2002). To quote from Falkowski et al. (2000), Our knowledge is insufficient to describe the interactions between the components of the Earth system and the relationship between... 

High-level waste (HLW), intermediate-level waste (ILW), and low-level waste (LLW) are produced at all stages of the nuclear fuel cycle as well as in the non-nuclear industry, research institutions, and hospitals. The nuclear fuel cycle produces liquid, solid, and gaseous wastes. Moreover, spent nuclear fuel (SNF) is considered either as a source of U and Pu for re-use or as radioactive waste (Johnson Shoesmith 1988), depending on whether the closed ( reprocessing ) or the open ( once-through ) nuclear fuel cycle is realized, respectively (Ewing, 2004). 

---