Plutonium processing corrosion

Though both hydrofluorination and reduction were accomplished with relative ease, three significant problems were apparent. First, PuFt is a neutron emitter, requiring considerable protective shielding and creating difficulty in handling. Secondly, the use of HF requires costly equipment which must be resistant to corrosion. Finally, the salt from the reduction, CaF2, is not discardable, and must be processed to recover residual plutonium. 

There are some data that indicate sulfate ion aids in the formation of a more easily filtered plutonium peroxide precipitate. Ganivet (7) found, for instance, that peroxide precipitated from a nitric acid medium containing sulfate had better settling characteristics than precipitates from comparable solutions to which no sulfate was added. However, sulfate in the precipitate is undesirable, because of the corrosive effects it can have on processing equipment. Mainland, et al, (8) showed that by careful control of the precipitation parameters, it was possible to effectively precipitate peroxide in the absence of sulfate. 

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. 

The scraps which arise during the fabrication of plutonium-containing nuclear fuels are collected and stored for some time before they are processed to recover the plutonium. Due to the decay of Pu-241, considerable amounts of Am-241 may build up in the stored material. At the Alkem company, plutonium is recovered from the scrap by anion exchange the americium which is not sorbed on the resin is collected in the combined effluents from the loading and wash steps. The effluents are concentrated by evaporation besides americium, the concentrated effluents contain major amounts of uranium, plutonium, corrosion products, and residues from chemical reagents. A typical composition is given below ... 

The laboratory methods for recovering and purifying plutonium were not suited for large-scale production. The ether extraction used on the cyclotron-produced plutonium is a safety hazard. The lanthanum fluoride precipitation step yielded a gelatinous product that is difficult to process and the aqueous fluorides produced serious equipment corrosion. Other processes were... 

Fuel composition may change from uranium to plutonium, and cladding from aluminum to zirconium to stainless steel. In some cases blankets, moderators, and coolants must be processed, and these will introduce thorium, beryllium, NaK, and bismuth to the chemical process. These changes in materials will present new chemical and corrosion problems in waste treatment processes and waste storage procedures. 

The specifications for purified uranium and plutonium to be recycled are summarized in Table 21.7. Comparing these data with those presented before sliows diat at t 1 y the fission product activity must be reduced by a factor of 10 and the uranium contrait in plutonium by a factor of 2 X 10. The large number of chemical elem its involved (FPs, actinides and corrosion products) make the separation a difficult task. Additional complications arise from radiation decomposition and criticality risks and from the necessity to conduct all processes remotely in heavily shielded enclosures under extensive health protection measures. As a result reprocessing is one of the most complicated chemical processes ever endeavored on an industrial scale. 

Pu(IV) and PuCVI) extract well from HCl solutions by amines, while Pu(ni) is poorly extracted, in analogy with the strong base anion exchange system. Plutonium chloride systems have found application mainly in analytical and radiochemical work rather than in processes because of the corrosive properties of HCl solutions. 

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