Actinide production

Recently there has been interest in the sorptive behavior of natural clays toward metal ions potentially present in radioactive wastes. Initial studies of the transplutonium elements have been carried out to define their sorption behavior with such materials ( ). However, it is also important to understand the stability of the clay-actinide product with regard to radiation damage and to be able to predict what changes in behavior may occur after exposure to radiation, so that accurate transport models may be constructed. 

Feed Adjustment. The tantalum-lined evaporator used to collect the actinide product solutions from a series of double oxalate precipitation runs also serves to adjust the composite product to a feed solution for a series of oxide production runs. Excess acid is removed by boiling the solution slowly to near dryness. The temperature is held at greater than 119°C for 5 h or more during boiling to ensure the destruction of all oxalates. After approximate dryness has been reached, the evaporator is cooled, 0.01 M HNO3 is added to dilute the actinides to less than 10 g/L (usually to 10-15 L, total volume) and a sample is taken to determine the acidity (typically 0.05-0.10 M) and to verify that the actinides are still in solution. The adjustment is completed by the addition of acid and evaporation to give an actinide concentration of about 10 g/L and an acid concentration of 0.20-0.35 M at the final volume. 

The transplutonium elements and the rare earths, or lanthanides, are so similar chemically that what is true for one group is generally true for the other. In practice, process development work is usually carried out with lanthanides, and frequently, all the solutions end up as analytical samples. Transplutonium elements, in contrast, are so valuable that the goal is the maximum yield of pure products. Accordingly, the methods and equipment developed with rare earth separations are applied directly to heavy actinide production separations. These may be quite small in scale, but this is "production" for some of these elements. 

The first application of pressurized ion exchange to lanthanide and actinide separations was initiated in 1967 to examine this technique for the final separation of trivalent actinides in the TRU facility. In initial work with rare earths, it was demonstrated that 200-mg quantities of Nd and Pr could be adequately separated in times under an hour (19). This pair is as difficult to separate as any actinide pair, and the time and scale of separation easily met the requirements projected for actinide production at TRU. Subsequently, separations of multimilligram quantities of all fifteen rare earths were demonstrated in times as short as about 1.5 h (20, 21). 

This involves the use of tertiary amine extraction of the An ions from acidic 11 M LiCl solutions. Spectroscopic studies have indicated that, in the cases of Am and Nd at least, the octahedral trianionic hexachloro complexes are extracted from 11 M LiCl. Stability constant data for the chloride complexing of Am , and Cfin media of ionic strength 1,0 have been reported. Tertiary amines also extract Pu and a study of extraction from nitrate media by trilaurylamine (TLA) in xylene has been reported. " This showed that the mass transfer rate was controlled by the reactions between Pu from the bulk phase and interfacially adsorbed TLA-HNOs. The separation of individual transplutonium elements from the Tramex actinide product may be achieved using ion exchange or precipitation techniques." ... 

At the tail end of a solvent extraction process, the solvents are separated from the solutes for recycle. In this application of solvent extraction, vacuum distillation is used to separate volatile zinc and magnesium from coprocessed uranium and plutonium and from the uranium product. Feed to vacuum distillation is solid alloy. Overhead and bottom products are likwise cast into a solid alloy. These vacuum distillation operations are conducted in separate cells. The actinide products are converted to oxide for fuel fabrication. 

Figure 3. Actinide recycle occurs between the subsystems within the WTF. Wastes enter the subsystems in the left column. Actual recovery occurs in the central column subsystems. A mixture of actinide nitrates is sent from Actinide Product Concentration to the fuel reprocessing plant for codenitration.

The chemistry of aqueous uranium is discussed in 16.3 together with the chemistry of the other actinides. Production of reactor fuel and reprocessing is described in Chapter 21. 

When the actinide products are removed from electrorefiners, the electrorefiner salts cover the metal. The cathodes are processed to distill adhering salt and to consolidate the actinide metals. These salts are recycled to the electrorefiner for further use (Westphal and Mariani, 2000 Westphal et al., 2002). In the case of the liquid cadmium cathode, the cadmium is... 

Ajou University developed AMBIDEXTER-NEC (Advanced Molten-salt Breakeven Inherently-safe Dual-function EXcellenTly-Ecological Reactor Nuclear Energy Complex). The objective of the reactor is to bum DUPlC fuel, minimize minor actinides production, and of course, generate electric power. To achieve the objectives, the AMBIDEXTER reactor core consists of two parts, a blanket and a seed. The blanket consists of only molten salt fuel (LeF-BeF2-(Th,U,Pu)F4), and the seed consists of the molten salt fuel and graphite moderator channel. The blanket area has very hard neutron spectrum, almost looks like fast reactor neutron spectium, and the seed area has a soft neutron spectium almost looks like PWR. Therefore, AMBIDEXTER can achieve low conversion ratio, about 0.298, ie, it is a burner reactor. The code developed to analyze AMBIDEXTER is called AMBIKIN2D. The code system consists of HELIOS, AMDEC, and AMBIKIN2D. 

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