Americium Purex process

After a few years of storage, the main radioactive heat emitters in HLW are 90Sr and 137Cs. In addition, extremely long-lived actinides—neptunium, plutonium, americium, and curium—should be collected for transmutation in the future. Therefore, different flowsheets can be proposed for waste processing. It is possible to extract each radionuclide in the special extraction (sorption) cycle, for example, uranium and plutonium in the PUREX process, and after that, minor actinides (MAs) by the TRUEX process,4 strontium by the SREX process,5,6 and cesium by sorption7 or extraction.8... 

In addition to the aqueous raffinates from the solvent extraction cycles of the Purex process, an actinide bearing waste stream will arise from the washing of the TBP/OK solvent prior to its recycle to the first cycle. These wastes will typically contain actinides in a mixed NajCOs/NaNOs solution which also contains HjMBP and HDBP. The uranium present will form soluble U complexes with carbonate, as discussed in Section 65.2.2.l(i). Carbonate complexation of Pu also leads to solubility in alkaline solutions and in Na2C03 media precipitation did not occur below pH 11.4, although precipitates did form on reduction to Pu One Pu" species precipitated from carbonate media has been identified as Pu(0H)3-Pu2(C03)3 H20. In 2M Na2C03 media, Np is oxidized by air to Np above pH 11.7 while Np either precipitates or is reduced above pH 13. The potential of the Am /Am " couple, in common with those of other actinides, becomes more cathodic with increasing carbonate concentration. In the total bicarbonate plus carbonate concentration range 1.2-2.3 M all the americium oxidation states from (III) to (VI)... 

As shown in Figure 6, diisodecylphosphoric acid (DIDPA) gives higher distribution ratios compared with those of DEHPA, being more suitable for using as extractant at higher acid concentrations. One M DIDPA diluted with normal paraffins can be used to recover americium and lanthanides from the HLW of PUREX process. 

Dissolution, described in Sec. 4.4, produces an aqueous solution of uranyl nitrate, plutonium(IV) nitrate, nitric acid, small concentrations of neptunium, americium, and curium nitrates, and almost all of the nonvolatile fission products in the fuel. With fuel cooled 150 days after bumup of 33,000 MWd/MT, the fission-product concentration is around 1700 Ci/liter. The fint step in the solvent extraction portion of the Purex process is primary decontamination, in which from 99 to 99.9 percent of these fission products are separated from the uranium and plutonium. Early removal of the fission products reduces the amount of required shielding, simplifies maintenance, and facilitates later process operations by reducing solvent degradation from radiolysis. 

Aluminum(III) hydroxyfluorides minerals, 846 Alzheimer s disease aluminum removal, 770 Amberlite LA 2 solvent extraction palladium and platinum, 809 Americium breeder reactor fuels Purex process, 955 reprocessing, 954 Purex process, 946,950 sequestering agents, 962 Americium(III) complexes carbonates... 

The P/T process will be coupled after an improved PUREX process that puts all technetimn, iodine, and neptunium into the waste fraction or into special fractions. Thus, the waste will contain fission products and minor actinides (americium and curium). The process will probably be a solvent extraction process although molten salt systems are also studied as an alternative. The main issue will be to obtain pure Am and Cm fractions for subsequent destruction, i.e., fractions that do not contain any lanthanides. Some of the lanthanides, which are chemically very similar to trivalent actinides, have very high neutron cross sections. Therefore, they must be removed to make actinide burning possible. In some cases, it may also be desirable to transmute some long-lived fission products, e.g., Tc and l, to more shortlived nuclides. 

In the AREVA version of the PUREX process, plutonium is removed from the uranium after the original extraction, converted to oxide and used in MOX fuel fabrication. Neptunium, americium, curium, and other remaining FPs (including lanthanides) are vitrified and incorporated in the HEW form (Richter et al., 2006). 

For future advanced nuclear systems, minor actinides are considered more as a resource to be recycled and transmuted than to be disposed of directly into a nuclear repository. A key feature of advanced fuel cycles technologies would be to separate M A and ultimately americium from curium. Several countries are investigating the separation of MA from a PUREX/COEX based process raffinate or a modified PUREX process raffinate using new extractant molecules with two potential options for actinide separations ... 

Americium and curium can be obtained from the aqueous waste of the Purex process. This americium is a mixture of Am and " Am. Isotopically pure Am, the decay product of " Pu, can be obtained from aged plutonium. Solvent extraction and ion-exchange procedures are used to recover americium from waste streams. Americium metal is produced by lanthanum reduction of the oxide, followed by vacuum distillation of the americium at 1400°C. 

Synthetic waste solutions which simulate those often encountered in the PUREX process were tested in a SLM system to determine the efficiency for decontamination by removal of transuranic elements, such as americium (5). Diethyl N,N-... 

There are two breeder reactor fuel cycles. One involves the irradiation of U/ Pu oxide fuel with fast neutrons and is at the prototype stage of development. The other involves the irradiation of Th/ U oxide fuel with thermal neutrons and is at the experimental stage. Fuel from the U/ Pu cycle may be reprocessed using Purex technology adapted to accommodate the significant proportion of plutonium present in the fuel. Increased americium and neptunium levels will also arise compared with thermal reactor fuel. The Th/ U fuel may also be reprocessed using solvent extraction with TBP in the Thorex (Thorium Recovery by Extraction) process. In this case the extraction chemistry must also take account of the presence of Pa arising as shown in Scheme 2. 

The Selective ActiNide Extraction (SANEX) process has been developed by Madic and Hill (Hill et al., 2002, 17-21 Madic et al., 2002). As part of the management of minor actinides, it has been proposed that the lanthanides and trivalent minor actinides (Am and Cm) should be removed from the PUREX raffinate by a process such as DIAMEX in France or TRUEX in the USA. To allow the actinides such as americium to be reused in industrial sources or used as fuel, the lanthanides must be removed. The lanthanides have large neutron cross sections and hence they would poison a neutron-driven nuclear reaction. 

Each of these elements may be used for production of nuclear fuel or other purposes. The recovery efficiency for uranium is reported as 99.87% and for plutonium 99.36%-99.51% (NEA 2012). The extended PUREX includes separation of neptunium and technetium as well as recovery of americium and curium that are also separated from each other by additional extraction stages as given in detail in the flowsheet (NEA 2012). The advanced UREX-i-3 process generates six streams after separation uranium for re-enrichment Pu-U-Np for mixed oxide fuel c for managed disposal Am-Cm to be used as burnable poisons and for transmutation high-heat-generating products (Cs and Sr) and a composite vitrified waste with all other fission products. Some fuel types may require preliminary steps like grinding to enable their dissolution. 

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