Plutonium nitrate, conversion

Figure 2. Integrated flowsheet used at the ALKEM plant for plutonium nitrate conversion combined with 241 Am separation and conversion...

Plutonium is subsequently stripped to an aqueous phase containing NH20H HN03 in the CC Column. In order to increase the plutonium concentration of the CC Column product, a portion of this stream (CAIS) is recycled to the CA Column after adjustment with HNO3. The remainder of the stream (CCP) is routed to the product concentrator. The resulting concentrated and purified plutonium nitrate solution is suitable feed to other processes for conversion to the desired product form (e.g., metal or plutonium dioxide). The remainder of the PRF solvent extraction system consists of a series of columns to wash the TBP-CCI4 solvent and prepare it for reuse. 

PuOj from direct calcination of Pu(N03 )4. The precipitation steps of the above processes can be avoided by the direct calcination of the plutonium nitrate solution to PuOa. Calcination has been carried out at 350 C in a liquid-phase screw calciner. Half a mole of ammonium sulfate per mole of plutonium is added to the feed solution to increase the production of reactive PuOi. The calcination time and temperature must be low enough to minimize sintering, which would otherwise reduce the chemical reactivity of the oxide particles for subsequent conversion to a halide. 

As part of this ongoing program, a redundant Plutonium Finishing Line (FL3) that consists of 21 stainless-steel gloveboxes, and which was operated between 1962 and 1985 for the conversion of plutonium nitrate to plutonium oxide and plutonium metal, is now being decommissioned and dismantled. 

PNC developed a co-conversion technology utilizing the microwave heating direct denitration process (MH method) which converts plutonium nitrate and uranyl nitrate solution to MOX powder. Compared with the conventional method, it is a simple process and generates less liquid waste. 

The most widely employed method for plutonium reprocessing used today in almost all of the world s reprocessing plants is the Purex (plutonium-uranium reduction extraction) process. Tributylphosphate (TBP) is used as the extraction agent for the separation of plutonium from uranium and fission products. In effecting a separation, advantage is taken of differences in the extractability of the various oxidation states and in the thermodynamics and kinetics of oxidation reduction of uranium, plutonium, and impurities. Various methods are in use for the conversion of plutonium nitrate solution, the final product from fuel reprocessing plants, to the metal. The reduction of plutonium halides with calcium proved to be the best method... 

Step 13. Add 5 mL of concentrated HN03 to the 100 mL beaker, swirl to mix, and gently heat on the hot plate to evaporate to a small liquid residue to remove the iodine. Complete the conversion of the plutonium to the nitrate form by two additional treatments with 5 mL portions of concentrated HN03. Evaporate to near dryness each time, but do not dry. 

In the Aquafluor process [G4] developed by the General Electric Company, most of the plutonium and fission products in irradiated light-water reactor (LWR) fuel are separated from uranium by aqueous solvent extraction and anion exchange. Final uranium separation and purification is by conversion of impure uranyl nitrate to UFg, followed by removal of small amounts of PuF , NpFg, and other volatile fluorides by adsorption on beds of NaF and Mgp2 and a final fractional distillation. A plant to process 1 MT/day of irradiated low-enriched uranium fuel was built at Morris, Illinois, but was never used for irradiated fuel because of inability to maintain on-stream, continuous operation even in runs on unirradiated fuel. The difficulties at the Morris plant are considered more the fault of design details than inherent in the process. They are attributed to the attempt to carry out aqueous primary decontamination, denitration, fluorination, and distillation of intensely radioactive materials in a close-coupled, continuous process, without adequate surge capacity between the different steps and without sufficient spare, readily maintainable equipment [G5, R8]. 

Many reprocessing plants are required to convert purified nitrates containing plutonium to oxides before shipment. Conversion processes are described in Chap. 9, Sec. 4.7. 

The plutonium purification may be achieved by additional TBP extraction cycles. U(IV) cannot be used as reductant in this part of the process. The final uranium and plutonium products are nitrate solutions whose conversion to oxides, fluorides, etc., have been described earlier ( 5.5.3). 

It was possible in a few cases to derive a coefficient relating the nitrate ion concentration to critical volume. The coefficient derived is the change in critical volume per gram of (NO ) change as nitric acid. The conversion to a correction for total (NO,") concentration is simply, performed by assuming that the plutonium is present as Pu(NO,),. For plutonium concentrations in the range of 47 to 98 g/f, the coefficient varied between 0.025 to 0.029 f/g NO,-. 

The fission and explosive energy release from criticality accidents involving liquid and metal assemblies has been well established from both accidents and experimentally induced excursion data however, very little work has been performed to date in dry or near-dry powder assemblies. Vfith. the possible advent of plutonium recycle it has become increasingly apparent that the upper limits of energy release for PuQi and PuOt-UOa assemblies similar to that found in nitrate to oxide conversion plants and mixed-Oxide fuel fabrication plants should be established. 

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