Hydroxylamine nitrate plutonium reductant

The Purex process, ie, plutonium uranium reduction extraction, employs an organic phase consisting of 30 wt % TBP dissolved in a kerosene-type diluent. Purification and separation of U and Pu is achieved because of the extractability of U02+2 and Pu(IV) nitrates by TBP and the relative inextractability of Pu(III) and most fission product nitrates. Plutonium nitrate and U02(N03)2 are extracted into the organic phase by the formation of compounds, eg, Pu(N03)4 -2TBP. The plutonium is reduced to Pu(III) by treatment with ferrous sulfamate, hydrazine, or hydroxylamine and is transferred to the aqueous phase U remains in the organic phase. Further purification is achieved by oxidation of Pu(III) to Pu(IV) and re-extraction with TBP. The plutonium is transferred to an aqueous product. Plutonium recovery from the Purex process is ca 99.9 wt % (128). Decontamination factors are 106 — 10s (97,126,129). A flow sheet of the Purex process is shown in Figure 7. 

Although the redox potentials for aqueous solution indicate that uranium(IV) should reduce plutonium(IV), anions and other complexing agents can change the potentials sufficiently that uranium(IV) and plutonium(IV) can coexist in solution (25). Since one of the products of photochemical reduction of uranyl by TBP is dibutyl phosphate (DBP), which complexes plutonium(IV) strongly, experiments were done to test the photochemically produced urani-um(IV) solutions as plutonium(IV) reductants (26). Bench-scale stationary tests showed these solutions to be equivalent to hydroxylamine nitrate solutions stabilized with hydrazine (27). 

Hydroxylamine salts were found to be good reductants of plutonium, under certain conditions ( 5). Interest in these reducing agents stemmed from the desire to avoid the introduction of metallic cations in the separated plutonium product. Hydroxylamine sulfate was used on a large scale at the Savannah River Plant (j>). While partitioning was satisfactory, the objectionable presence of sulfate ions led to the adoption of hydroxylamine nitrate (HAN). The reaction mechanism and kinetics of the HAN reduction of plutonium have been studied extensively The... 

Plutonium trifluoride. Plutonium trifluoride can be converted directly to plutonium metal, or it is an intermediate in the formation of PUF4 or PUF4 -PUO2 mixtures for thermochemical reduction, as described in Sec. 4.8. The stabilized Pu(III) solution, produced by cation exchange in one of the Purex process options for fuel reprocessing, is a natural feed for the formation of plutonium trifluoride, as is shown in the flow sheet of Fig. 9.9 [03]. A typical eluent solution from cation exchange consists of 30 to 70 g plutonium/liter, 4 to 5 Af nitric acid, 0.2 Af sulfamic acid, and 03 Af hydroxylamine nitrate. The sulfamic acid reacts rapidly with nitrous acid to reduce the rate of oxidation of Pu(III) to about 4 to 6 percent per day. Addition of ascorbic acid to the plutonium solution just before fluoride precipitation reduces Pu(IV) rapidly and completely to Pu(III). 

Once plutonium and uranium are coextracted and codecontaminated, plutonium is separated from uranium in the partitioning contactor by reduction to Pu(III) with a reduc-tant. Over the years, a number of plutonium reductants have been proposed. The most widely used reductant to partition plutonium from uranium in the PUREX process was (Fe(S03NH2)2) other alternates were proposed such as hydrazine-stabilized ferrous nitrate or uranous nitrate, and hydroxylamine salts. 

Me Kibben, J.M. and J.E. Bercaw, 1971. Hydroxylamine nitrate as a plutonium reductant in the PUREX solvent extraction process. Report DP-1248. Aiken, SC Savannah River Laboratory. 

Ferric nitrate could be used to catalyze the reduction of plutonium by hydroxylamine during partitioning (3). A laboratory test with a mixture of Fe(N03)3 and HAN resulted in Pu reflux (Figure 5). Using Fe(N03)2 instead of Fe(N03)3 merely shifted the point of reflux toward the feed stage. The reflux must be caused by N02 because a plant test at Hanford with Fe(N03)2 and N2Hi was successful except when excess N02 entered the partitioning column (6). 

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