Reprocessed uranium fuel

Figure 8.9 Principal contributions to the long-term ingestion toxicity of high-level waste from reprocessing uranium fuel (fuel from uranium-fueled PWR, 33 MWd/kg, 0.5 percent of uranium and plutonium appear in waste).

An improved solvent extraction process, PUREX, utilizes an organic mixture of tributyl phosphate solvent dissolved in a hydrocarbon diluent, typically dodecane. This was used at Savannah River, Georgia, ca 1955 and Hanford, Washington, ca 1956. Waste volumes were reduced by using recoverable nitric acid as the salting agent. A hybrid REDOX/PUREX process was developed in Idaho Falls, Idaho, ca 1956 to reprocess high bum-up, fuUy enriched (97% u) uranium fuel from naval reactors. Other separations processes have been developed. The desirable features are compared in Table 1. 

Since the amount of fissile material in the fuel assemblies is only about 3 percent of the uranium present, it is obvious that there cannot be a large amount of radioactive material in the SNF after fission. The neutron flux produces some newly radioactive material in the form of uranium and plutonium isotopes. The amount of this other newly radioactive material is small compared to the volume of the fuel assembly. These facts prompt some to argue that SNF should be chemically processed and the various components separated into nonradioac-tive material, material that will be radioactive for a long time, and material that could be refabricated into new reactor fuel. Reprocessing the fuel to isolate the plutonium is seen as a reason not to proceed with this technology in the United States. 

Development efforts in the nuclear industry are focusing on the fuel cycle (Figure 6.12). The front end of the cycle includes mining, milling, and conversion of ore to uranium hexafluoride enrichment of the uranium-235 isotope conversion of the enriched product to uranium oxides and fabrication into reactor fuel elements. Because there is at present a moratorium on reprocessing spent fuel, the back end of the cycle consists only of management and disposal of spent fuel. 

Nuclear Fuel Reprocessing. Spent fuel front a nuclear reactor contains - tsy easy cwpu Mc-py, ant many other radioaclive isnlopes (fission products). Reprocessing involves the treatment of the spent fuel to separate plutonium and unconsumed uranium from other isotopes so that these can be recycled or safely stored. 

All the components of the nuclear-fission power system are fully operational except for ultimate waste disposal. However, spent fuel is not reprocessed in the United States because there is currently an adequate supply of natural uranium and enrichment services availab 1 e domestically and from other countries at a 1 ower cost than that of the recovered fissionable material from spent fuel. Also, the United States unilaterally declared a moratorium on reprocessing in the early 1980s in an attempt to reduce the spread of nuclear weapons. Current economics do not favor a return to reprocessing and fuel recycling in the United States at this time in as much as it does dramatically increase the amount of interim and final waste storage capacity that is required. 

The major use of C1F3 is in the nuclear industry which converts unclean spent fuel reprocessing, uranium metal into gaseous uranium hexafluoride. Other applications are low temperature etchant for single crystalline silicon [63,64], It is also used as a fluorinating reagent and in the synthesis of GIF and conversion of metals to metal fluorides such as tantalum and niobium metals to tantalum pentafluoride and niobium pentafluoride, respectively. 

The technology required to reprocess nuclear fuel and extract plutonium is much simpler than that required to enrich uranium however the use of HEU as a weapons material does not necessarily require the use of a reactor. HEU can be obtained by reprocessing MTR fuel which is available in many countries. 

The starting materials for uranium nuclear fuels are uranium compounds from natural uranium deposits and fissile material separated by reprocessing from spent uranium fuel rods. 

Zinc Distillation Process ( 3, 4 ). A zinc distillation process was selected as a reference pyrochemical process that would have a sufficient degree of proliferation resistance that it could be used by nonweapons nations to reprocess spent fuel without significantly increasing their weapons production capability. The process has the inherent proliferation-resistant advantages of being a low decontamination process with limited plutonium enrichment in uranium-plutonium-zinc mixtures. The process chemistry flow sheet for this process is shown in Figure 1. 

Aqueous Process. In 1967-68, a hot reprocessing test had been conducted using the spent fuel (ca. 600 MWD/T) from JRR-3 (Japan Research Reactor-3) (6). About 200 g of purified plutonium was recovered by a modified PUREX process from aluminum-claded uranium fuels of natural isotopic composition. 

Decontamination from fission products was good except for 95Zr (Table 4) and is comparable to that achieved in reprocessing irradiated enriched uranium fuels (2). 

Larger samples are only partially chlorinated, since molten PuClj prevents the reaction going to completion [234], whereas plutonium(Hl) oxalate is completely converted into PuClj at 600-650 C, but the product is contaminated with carbon [234]. Plutonium(III) "carbonate", in contrast, is quantitatively converted between 4(X> and 550 C [234]. Phosgene has been used in a laboratory study upon the reprocessing (by chlorination) of neutron-irradiated uranium fuels [1491]. 

The fast-spectrum reactors with full recycle of actinides would be designed with on-site spent fuel reprocessing and fuel fabrication to minimize the on-site inventory of long-lived radioactive waste. Modern robotic equipment can be used for reactor refueling and for fuel reprocessing. The spent fuel reprocessing and fuel fabrication facilities must be developed to close the nuclear fuel cycle and use all the energy available in natural uranium. 

The total demand of natural uranium from 2000 to 2150 is shown in Figure 10. Lines 1 and 2 shown in Figure 10 indicate the total demand of natural uranium necessary for LWRs using the enriched uranium fuel without fuel reprocessing and the reprocessed fuels (the MOX fuels), respectively. It is clear that the fuel reprocessing is effective for reducing the demand of natural uranium. 

M. SPENT FUEL REPROCESSED, URANiUM AND PLUTONiUM RECYCLED Recovered Pu, 445 kg... 

Under some conditions it is economically attractive or environmentally preferable to reprocess spent fuel in order to (1) recover uranium to be recycled to provide part of the enriched uranium used in subsequent lots of fuel, (2) recover plutonium, and (3) reduce radioactive wastes to more compact form. In part II of Fig. 1.11 the recovered 0.83 percent enriched uranium is recycled and the 244 kg of plutonium recovered per year is stored for later use in either a light-water reactor or a fast-breeder reactor. This recycle of uranium to the isotope separation plant reduces the annual UaOg feed rate to 220 short tons, still appreciably greater than for the heavy-water reactor. 

There are several reasons why it is useful to store or cool irradiated uranium fuel for several months prior to shipment for reprocessing ... 

The long-term radioactivities of neptunium, americium, and curium in the high-level reprocessing wastes from the uranium-fueled water reactor are shown in Fig. 8.7. Except for Am and Np, these curves are also applicable to unprocessed discharge fuel. The curves Am and Np have been calculated for 0.5 percent of the plutonium in discharge fuel to appear in the wastes, so that there is not sufficient Pu to significantly increase the amounts of Am and... 

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