Fused salt processing of impure plutonium dioxide to high-purity plutonium metal

Abstract

We have developed a process for converting impure plutonium dioxide ("^96% pure) to high-purity plutonium metal (>99.9%). The process consists of reducing the oxide to an impure plutonium metal intermediate with calcium metal in molten calcium chloride. The impure intermediate metal is cast into an anode and electrorefined to produce high-purity plutonium metal. The oxide reduction step is being done now on a O.6-kg scale with the resulting yield being >99.5%. The electrorefining is being done on a 4.0-kg scale with the resulting yield being 80-85%. The purity of the product, which aver¬ ages 99.98%, is essentially insensitive to the purity of the ieed metal. The yield, however, is directly dependent on the chemical composition of the feed. To date, approximately 250 kg of impure oxide has been converted to pure metal by this processing sequence. The availability of impure plutonium dioxide, together with the need for pure plutonium metal, makes this sequence a valu¬ able plutonium processing tool. I. '1 20 Max' 0.50 Hax c C Values ntighc be raised if these limits present a problem. Carbon is removed in the oxide roasting step. The carbon co of an electrorefining feed, however should not exceed 0.3&%.

Wastes from plutonium conversion and scrap recovery operations

“…13 " 14 If the oxalates are heated in air to 800°C to remove residual carbon and acids, the resulting oxide is suitable for DOR. 15 As we note later, some precipitated plutonium fluorides can also be precursors for reduction to the metal. 16 ' 17 • Precipitation of plutonium and americium hydroxides from waste solutions such as oxalate or peroxide filtrates is an effective method to allow discard of the alkaline filtrate and recycle of the plutonium and americium in the separated solids.…”

Water Solubility of Plutonium and Uranium Compounds and Residues at TA-55

“…In the direct oxide reduction (DOR) process, plutonium dioxide is reduced by calcium metal in molten CaCl 2 solvent to form plutonium metal and calcium oxide. [31][32][33] A typical plutonium DOR salt is illustrated in Figure 3-14. These salts are largely CaCl 2 but may contain CaO, finely divided Ca metal and Pu shot which may subsequently be oxidized to PuO 2 .…”

Plutonium and Plutonium Compounds

“…In the DOR process, PuO 2 is reduced with calcium metal to produce plutonium metal and CaO (50,53,54). The reaction takes place in a molten CaCl 2 or CaCl 2 ÀCaF 2 solvent, which dissolves the resulting CaO and allows the plutonium metal to coalesce in the bottom of the crucible to form a metal button.…”

“…In the ER process, liquid plutonium oxidizes from the anode ingot into a molten-salt electrolyte where the Pu(III) ion is transported through the salt to the cathode, where it is reduced back to metal (53,58). The liquid metal drips off the cathode and into the annular space to produce an annular metal casting, or ER ring.…”