Plutonium processing fertilizer

In addition to fissionable isotopes ( U, or plutonium) and fertile isotopes ( U or thorium), spent fuel from a reactor contains a large number of fission product isotopes, in which all elements of the periodic table from zinc to gadolinium are represented. Some of these fission product isotopes are short-lived and decay rapidly, but a dozen or more need to be considered when designing processes for separation of reactor products. The most important neutron-absorbing and long-lived fission products in irradiated uranium are listed in Table 1.4. 

Uranium-235 and U-238 behave differently in the presence of a controlled nuclear reaction. Uranium-235 is naturally fissile. A fissile element is one that splits when bombarded by a neutron during a controlled process of nuclear fission (like that which occurs in a nuclear reactor). Uranium-235 is the only naturally fissile isotope of uranium. Uranium-238 is fertile. A fertile element is one that is not itself fissile, but one that can produce a fissile element. When a U-238 atom is struck by a neutron, it likely will absorb the neutron to form U-239. Through spontaneous radioactive decay, the U-239 will turn into plutonium (Pu-239). This new isotope of plutonium is fissile, and if struck by a neutron, will likely split. 

Other Pyrochemical Processes. The chemistry of pyrochemi-cal separation processes is another fertile area of research e.g., new molten salt systems, scrub alloys, etc. and the behavior of plutonium in these systems. Studies of liquid plutonium metal processes should also be explored, such as filtration methods to remove impurities. Since Rocky Flats uses plutonium in the metal form, methods to convert plutonium compounds to metal and purify the metal directly are high-priority research projects. 

The chemistry of waste treatment processes and the development of new processes are fertile areas of research work. The speciation of plutonium in basic and laundry wastes is needed. For example, if soluble plutonium complexes in basic wastes can be destroyed, perhaps ultrafiltration could replace the flocculent-carrier precipitation process. The chemistry of plutonium(VII) and of ferrites—a candidate waste treatment process—needs to be explored.(23)... 

In a typical fast breeder nuclear reactor, most of the fuel is 238U (90 to 93%). The remainder of the fuel is in the form of fissile isotopes, which sustain the fission process. The majority of these fissile isotopes are in the form of 239Pu and 241Pu, although a small portion of 235U can also be present. Because the fast breeder converts die fertile isotope 238 U into the fissile isotope 239Pu, no enrichment plant is necessary. The fast breeder serves as its own enrichment plant. The need for electricity for supplemental uses in the fuel cycle process is thus reduced. Several of the early hquid-metal-cooled fast reactors used plutonium fuels. The reactor Clementine, first operated in the Unired States in 1949. utilized plutonium metal, as did the BR-1 and BR.-2 reactors in the former Soviet Union in 1955 and 1956, respectively. The BR-5 in the former Soviet Union, put into operation in 1959. utilized plutonium oxide and carbide. The reactor Rapsodie first operated in France in 1967 utilized uranium and plutonium oxides. 

In an energy system based on breeder reactors, it is necessary to process the used fuel elements to recover the fertile elements and discard the waste products. The difficulty with this approach lies in the handling of the uranium, plutonium and highly radioactive nuclear fission products. 

There is no change in the view that the ultimate role of fast reactors is to make available the very large reserves of U-238 and other fertile isotopes, and by means of the breeding process to turn them into fissile isotopes such as Pu-239 and then fission them to generate useful energy in the form of heat. However in the medium term, before the breeding role is economically demanding, fast reactors have other purposes. One of these is to consume plutonium. 

Nuclear reactors can be designed on the basis of their fuel cycle such that they breed more fissile nuclides than what they use. Breeder reactors can utilize uranium, thorium, and plutonium resources more efficiently. There are two types of breeder reactors (1) fast neutron spectmm breeder and (2) thermal neutron spectmm breeder reactors, which are designed based on (99.2% natural abundance) and Th (100% natural abundance), respectively. Fertile nuclides and Th capture neutrons and trans-form, respectively, to fissile nuclides Pu and U. Through this process, which is known as breeding, the reactor produces more fissile nuclides than what it consumes. Fast-breeder reactors (FBRs) can also be used in order to transmute the long-lived... 

Neptunium and protactinium complete the listing of fissile and fertile materials, since these are intermediates in the production of plutonium and U233 from XJ238 thorium. Limited exploratory studies of their solubilities have been carried out primarily in connection with the development of processes for their continuous removal from blanket systems. 

The variable processing charges arising from labor, materials, and other factors dependent on the throughput of fuel and fertile material are represented by Rqs. (10-1) and (10-2) for processing thorium-uranium mixtures and uranium-plutonium mixtures, respectively. 

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