Fission products recovery from wastes

Rizvi, G.H. et al.. Recovery of fission product palladium from acidic high level waste solution, Sep. Sci Technol, 31(13), (1996), ppI80S-1816. 

After several runs of the electrolysis process, the active metal fission products such as alkali, alkaline earth and rare earth metals are accumulated in the molten salt. The accumulated fission products must be removed from the molten salt because they will affect the recovery efficiency of U and TRU. Periodically, the molten salt is removed from the electrolysis cell, purified using the salt purification process and recycled to the electrolysis cell. However, the molten salt always contains U and TRU with the fission products because the electrolysis is used to recover pure U and TRU without fission products. Therefore, fission products removed from the molten salt are always accompanied by some amount of U and TRU. It is necessary to optimize between the loss of U and TRU and the quantity of fission products removed because an increased removal of the fission products results in an increased contamination by the TRU in the waste stream. 

Table 2.5 summarizes the developments at the four major stages of the PUREX process. The success of the process is measured by the quantitative recovery (>99.9%) of U and Pu with high DFs (DF > 106) from the fission products and structural materials. There is also growing concern about the volumes of radioactive waste generated during fuel reprocessing. There have been continuous R D efforts in radiochemical laboratories toward these ends. 

The process sequence now used is shown in Fig. 4. Since only about 5% of the fission products are disposed of in waste solutions from the Tramex batch extraction, that process serves primarily as a feed pretreatment for the LiCl AIX. The Tramex product contains about 98% of the transcurium elements and can be processed quickly to maximize the recovery of 253Es which has a 20-d half-life. As time permits, the "clean rework" can be processed to recover the remaining actinides. 

One possible application in which large amounts of rare earths and actinides would be processed occurs in some schemes for nuclear waste management. If it should prove to be advantageous to remove transplutonium elements from nuclear waste, for example, the recovery of Am and Cm from the much larger amounts of rare earths would be required. This problem has been investigated by the author in tracer tests with rare earth mixtures typical of fission products, using a heavy rare earth such as holmium as a stand-in for Am and Cm (Fig. 5). It is clear that the bulk of the holmium can be recovered in reasonable purity, and that the bulk of the lighter rare earths is effectively separated from the very small amount of heavy rare earths, Am, and Cm. 

Figure 39.12). The presence of important fission products such as Cs and Ru did not affect the recovery of uranium. This clearly indicates that the present method could be successfully apphed to the recovery of both U(VI) and Pu(TV) from oxalate supernatant waste. 

Exchange resins are also employed for the concentration of ions present in very dilute solutions instances are the recovery of silver from photographic residues, chromate from the waste liquor of chromium plating and magnesium from sea water. They have also been used for the separation of rare earths (p. 426), and of uranium, plutonium and radio-active fission products (p. 437), and for plutonium and uranium-233 purification. A striking application was the historic separation of single atoms of mendelevium on a sulphonated polystyrene resin and their elution therefrom, at 87 , with a-hydroxyisobutyrate (Seaborg, 1955). 

However, a tabulation of properties of typical WCF calcine incorporated by various post treatment methods is given in Table VII (13), Also shown are the properties of the untreated WCF calcine. In some instances the numerical values of the property vary by several orders of magnitude, while in others only qualitative terms are used. The term retrievability is very important and can mean either a simple recovery (e.g., as from the WCF storage bins) in preparation for packaging and shipping to a repository, or recovery and use or conversion to another form. For example, if one converts a calcined waste to a glass or ceramic block, the unit may be easily retrievable for shipment but may be very difficult to process to another form or to recover specified fission products. On the other hand, untreated WCF calcine has had a minimum of treatment, can be converted to any other form, can be readily processed for desired components, and is fully retrievable. 

Low-heat wastes contain relatively small quantities of fission products and associated decay heat. These wastes (Table II) consist of stored BiP04 process and early Redox process wastes, tributyl phosphate process wastes from an early uranium recovery program, process solvent wash wastes, and fuel cladding removal wastes. 

The hot run was made with the feed solution obtained by dissolving highly irradiated Pu-Al alloy in HNO3 with mercuric ion catalyst. Uranium was added to the solution to produce a typical Purex feed. Uranium and most of the plutonium were recovered by the normal Purex process. The aqueous waste containing Am, Cm, Cf, fission products, Al, and Hg was evaporated and acid was stripped to produce the feed (Table 2). The results are as expected from the laboratory tests excellent recovery of Pu, Am, and Cm but low decontamination factors (DF). 

IV. Recovery of Fission Products from Radiochemical Wastes. 108... 

To rather selectively separate pertechnetate, with more than 90 % yield, from solutions of acid fission products it was proposed to use finely divided cadmium sulphide. The overall yield of the radionuclide pure c, finally extracted as [(C(,H5)4As TcC)4, was 68 % [182,183]. In addition, activated carbon was used to efficiently separate pertechnetate from high-level liquid waste. Distribution coefficients of more than 500 were observed when pertechnetate was separated with activated carbon from a 2 M HNO3 solution [184]. Effective separation and recovery of Tc04 from contaminated groundwater with activated carbon have been reported very recently [185. ... 

There are many examples of the studies on SLM for nuclear applications in the literature. SLMs were tested for high-level radioactive waste treatment combined with removal of actinides and other fission products from the effluents from nuclear fuel reprocessing plants. The recovery of the species, such as uranium, plutonium, thorium, americium, cerium, europium, strontium, and cesium, was investigated in vari-ons extracting-stripping systems. Selective permeation... 

Recovery of Fission Products FROM Radioactive Waste... 

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