Recycling uranium

Figure 3.32 Fuel-cycle flow sheet for 1000-MWe LWR fueled with natural uranium, recycle plutonium, and plutonium recovered from reactor fueled with enriched uranium. Basis 1 year, 80 percent capacity factor.

For operation of the model reactor, the input of uranium to the model plant converting UO2 to UF6 is assumed to be 182 t of natural uranium which is processed to about 270 t of UFe- 13.2 wt% of 270 t of UFf, is from uranium recycled back to the system. As mentioned above, 0.14 kg of Tc per reactor year is returned with uranium to the fuel cycle, where it reacts with fluorine to give TcF6. An estimate of the source term for Tc released to the atmosphere and to water can be formed by assuming that TcFfi is released to each pathway in the same fraction of fluoride appearing in the effluent to the total fluoride used in the process 6]. The total amount of fluoride used in the model plant for fluorination is at least 270 t of UFV, minus 182 t of uranium, i. c. 88 t. Releases of fluoride to water account for 0.22 t and to the atmosphere for 0.11 t per model reactor year. (Consequently, it may be assumed that the fraction 0.22/88 of... 

Predictions in the 1960s of the growth in nuclear power indicated the need for recycling (qv) of nuclear fuels. RadionucHdes involved are uranium-235, uranium-238 [24678-82-8] and plutonium-239. This last is produced by neutron absorption in the reactions ... 

Uranium-239 [13982-01 -9] has a half-life of 23.5 min neptunium-239 [13968-59-7] has a half-life of 2.355 d. Recycling or reprocessing of spent fuel involves separation of plutonium from uranium and from bulk fission product isotopes (see Nuclearreactors, chemical reprocessing). 

Supply Projections. Additional supphes are expected to be necessary to meet the projected production shortfall. A significant contribution is likely to come from uranium production centers such as Eastern Europe and Asia, which are not included in the capabihty projections (27). The remaining shortfall between fresh production and reactor requirements is expected to be filled by several alternative sources, including excess inventory drawdown. These shortfalls could also be met by the utili2ation of low cost resources that could become available as a result of technical developments or pohcy changes, production from either low or higher cost resources not identified in production capabihty projections, recycled material such as spent fuel, and low enriched uranium converted from the high enriched uranium (HEU) found in warheads (28). 

The recycle weapons fuel cycle rehes on the reservoir of SWUs and yellow cake equivalents represented by the fissile materials in decommissioned nuclear weapons. This variation impacts the prereactor portion of the fuel cycle. The post-reactor portion can be either classical or throwaway. Because the avadabihty of weapons-grade fissile material for use as an energy source is a relatively recent phenomenon, it has not been fully implemented. As of early 1995 the United States had purchased highly enriched uranium from Russia, and France had initiated a modification and expansion of the breeder program to use plutonium as the primary fuel (3). AH U.S. reactor manufacturers were working on designs to use weapons-grade plutonium as fuel. 

Uranium oxide [1344-57-6] from mills is converted into uranium hexafluoride [7783-81-5] FJF, for use in gaseous diffusion isotope separation plants (see Diffusion separation methods). The wastes from these operations are only slightly radioactive. Both uranium-235 and uranium-238 have long half-Hves, 7.08 x 10 and 4.46 x 10 yr, respectively. Uranium enriched to around 3 wt % is shipped to a reactor fuel fabrication plant (see Nuclear REACTORS, NUCLEAR FUEL reserves). There conversion to uranium dioxide is foUowed by peUet formation, sintering, and placement in tubes to form fuel rods. The rods are put in bundles to form fuel assembHes. Despite active recycling (qv), some low activity wastes are produced. 

If the economics of recycling were improved, that option would become preferable for spent fuel because the permanent repository issues of the residual fission products would be simpler. The economic value of the energy generated from the recycled plutonium and uranium would substantially allay the costs of the repository as compared to the spent fuel throwaway option. 

Losses are kept to a minimum by carbonation of the mother Hquor with CO2 and recycle of the carbonated product back to the leach system. From acid solutions, uranium is usually precipitated by neutralization with ammonia or magnesia. Ammonia gives an acceptable precipitate, for which compositions such as (NH 2(U02)2S04(0H)4 were calculated. The ammonium salt is preferred if the product is to be used ia the manufacture of... 

The last reaction cited above as shown is very effectively catalyzed by bacterial action but is very slow chemically by recycling the spent ferrous liquors and regenerating ferric iron bacterially, the amount of iron which must be derived from pyrite oxidation is limited to that needed to make up losses from the system, principally in the uranium product stream. This is important if the slow step in the overall process is the oxidation of pyrite. The situation is different in the case of bacterial leaching of copper sulfides where all the sulfide must be attacked to obtain copper with a high efficiency. A fourth reaction which may occur is the hydrolysis of ferric sulfate in solution, thus regenerating more sulfuric acid the ferrous-ferric oxidation consumes acid. 

Nuclear fuel reprocessing was first undertaken with the sole purpose of recovering plutonium, for weapons use, from uranium irradiated in nuclear reactors. These reactors, called the production reactors, were dedicated to transmuting as much of the uranium as possible to plutonium. From its original scope of recovering exclusively plutonium, with no attempts to either recover or recycle uranium, nuclear fuel reprocessing has since grown into a much more sophisticated and complex operation with expanded scope. It is now called upon to separate uranium and plutonium from the fission products, and to purify these elements to levels at which these fissile materials can be conveniently recycled for reuse. The present scope also extends to fission products separation and concentration. 

Stripping the uranium from the solvent can be accomplished by using either acid or alkaline solutions. If an alkali carbonate solution is used, the stripped solvent then requires equilibrating with sulfuric acid before recycling to the extraction stage. Sulfuric acid stripping obviates the need for such equilibration. 

Tertiary amines are susceptible to oxidation (RsNiO), and some evidence has been found to suggest that oxidation does indeed occur after several months recycling in a uranium solvent extraction circuit [A. W. Ashbrook, unpublished data]. 

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