Sulfamate, ferrous uranium-plutonium partitioning

In the Purex process, plutonium and uranium are coextracted into an organic phase and partitioned by reducing plutonium(IV) to the aqueous-favoring plutonium(III). This has been achieved chemically by use of a suitable reductant such as ferrous sulfamate ( 1) or uranium(IV). (2, 3, 4, 5) The use of ferrous sulfamate results in accelerated corrosion of the stainless steel, due to the presence of ferric ions and sulfuric acid, and in an increase in the volume of wastes. The use of natural uranium(IV) can cause dilution of the 235U in slightly enriched uranium, thus lowering the value of the recovered uranium. 

Ferrous sulfamate has been the reductant for plutonium during partitioning of uranium and plutonium in the Purex process at SRP since startup. In recent years, a desire to reduce waste volumes has led to studies of alternative reductants or combinations of FeSA with other reductants. The FeSA in the Pu strip solution produces Fe(OH) 3 and Na2S0i in neutralized waste these compounds account for a large percentage of the solid material in Purex low activity waste. In an effort to reduce these wastes, we investigated HAN as a substitute for part or all of the FeSA in the Purex first cycle. 

In the partition contactor, plutonium was converted to inextractable, trivalent Pu (N03)3 by a reductant solution of ferrous sulfamate containing aluminum nitrate to keep uranium in the hexone phase. Plutonium was thus separated from uranium and transferred back to the aqueous phase along with the aluminum nitrate. Impure plutonium nitrate was purified by additional cycles of solvent extraction, not shown. 

In the IB column remaining traces of plutonium are stripped from the solvent by a strippant IBX, stream 10, containing hydrazine as holding reductant. A decontamination factor of 200 for removal of plutonium from uranium is anticipated for the IB columns. The big advantage of this partitioning system is that it adds no nonvolatile materials such as ferrous sulfamate to the system. 

Hanfoid [D3]. Nitrite concentration in feed to the HA column of a standard Purex plant was adjusted to route most of the neptunium in inadiated natural uranium into the extract from the HS scrubbing column. Sufficient ferrous sulfamate was used in the partitioning column to reduce neptunium to Np(IV), which followed uranium. This neptunium was separated from uranium by fractional extraction with TBP in the second uranium cycle. The dilute neptunium product was recycled to HA column feed, to build up its concentration. Periodically, irradiated uranium feed was replaced by unirradiated uranium, which flushed plutonium and fission products from the system. The impure neptunium remaining was concentrated and purified by solvent extraction and ion exchange. 

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