Neptunium Purex process

Purex process, 6, 951 Neptunium complexes, 3, 1131-1215 cupferron, 2, 510 Neptunium dioxide ions disproportionation Purex process, 6, 950... 

Uranium stripping Dilute HNO3 solutions at 45-50°C are used to remove uranium from the TBP phase. Traces of the fission products ruthenium and zirconium are eliminated in the second and third cycles of the Purex process. Also, in the second and third cycles, neptunium and the last traces of plutonium are removed from the uranium product. 

Uchiyama, G., Asakura, T., Hotoku, S., Fujine, S. 1998. The separation of neptunium and technetium in an advanced PUREX process. Solvent Extr. Ion Exch, 16 (5) 1191-1213. 

Anyun, Z., Jingxin, H., Xianye, Z., Fangding, W. 2001. Hydroxylamine derivatives in PUREX process, VI. Study on the partitioning of uranium/neptunium and uranium/ plutonium with N,N-diethylhydroxylamine in the purification cycle of uranium contactor. Solvent Extr. IonExch. 19 (6) 965-979. 

Zhu, Z., He, J., Zhang, Z. et al. 2004. Uranium/plutonium and uranium/neptunium separation by the Purex process using hydroxyurea. J. Radioanal. Nucl. Chem. 262 (3) 707-711. 

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... 

Reduction and oxidation (redox) steps are major process steps in the Purex process. Use is made of redox reactions to alter the valency of plutonium, uranium or neptunium with the object of producing these metals with a high degree of purity. 

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. 

This section describes processes for recovering neptunium from irradiated uranium. Neptunium is an example of one of the numerous elements in irradiated fuel that could be recovered as by-products of extraction of uranium and plutonium in the Purex process,... 

Distribution coefficients of neptunium in 30 v/o TBP depend on neptunium valence, temperature, and concentrations of uranyl nitrate, nitric acid, and other nitrates. At the nitric acid concentraticHis below 4 M usually used in Purex processes, the distribution coefficient of hexavalent neptunium is hi er than that of tetravalent neptunium at the same nitric acid and uranyl nitrate concentrations. Both are much higher than that of pentavalent neptunium. Both tetravalent and hexavalent neptunium are extracted as the complexes with two molecules of TBP, Np (N03)4 2TBP and Np 02(N03)2-2TBP. 

In the HA extracting and HS scrubbing sections of the Purex process, pentavalent neptunium is partially oxidized to the hexavalent state by nitrate ion,... 

Reduction of neptunium. To separate neptunium from plutonium in the Purex process, plutonium is reduced to inextractable Pu(IlI) while neptunium is reduced from extractable... 

Process selection. The processes just described recovered neptunium only partially and in variable yield because of the difficulty in controlling the distribution of neptunium valence between 5 and 6 in the primary extraction step with nitrite-catalyzed HNO3 and the incomplete reduction of neptunium from valence 5 to 4 in the partitioning step with feirous ion. This section describes a modified Purex process that could be used if more complete recovery of neptunium were required. It is based on process design studies by Tajik [Tl]. The principal process steps are shown in the material flow sheet Fig. 10.32. In the primary decontamination step, pentavalent vanadium oxidizes neptunium to the extractable hexavalent state. In the partitioning step, tetravalent uranium reduces plutonium to the inextractable trivalent state while converting neptunium to the still-extractable tetravalent state. 

Figure 10.32 Principal steps in Purex process modified for neptunium recovery. Circles indicate relative volume flow rate -----organic.

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